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Versions: (draft-popp-cnrp) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 3367

 Network Working Group                                            N. Popp
 Internet-Draft                                     RealNames Corporation
 Expires: July 9, 2002                                        M. Mealling
                                                           VeriSign, Inc.
                                                               M. Moseley
                                                            Netword, Inc.
                                                          January 8, 2002
 
 
                  Common Name Resolution Protocol (CNRP)
                          draft-ietf-cnrp-11.txt
 
 Status of this Memo
 
    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.
 
    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups.  Note that
    other groups may also distribute working documents as Internet-
    Drafts.
 
    Internet-Drafts are draft documents valid for a maximum of six months
    and may be updated, replaced, or obsoleted by other documents at any
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    material or to cite them other than as "work in progress."
 
    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt.
 
    The list of Internet-Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html.
 
    This Internet-Draft will expire on July 9, 2002.
 
 Copyright Notice
 
    Copyright (C) The Internet Society (2002).  All Rights Reserved.
 
 Abstract
 
    People often refer to things in the real world by a common name or
    phrase, e.g., a trade name, company name, or a book title.  These
    names are sometimes easier for people to remember  and type than
    URLs.  Furthermore, because of the limited syntax of URLs, companies
    and individuals are finding that the ones that might be most
    reasonable for their resources are being used elsewhere and so are
    unavailable.  For the purposes of this document, a "common name" is a
    word or a phrase, without imposed syntactic structure, that may be
 
 
 
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    associated with a resource.
 
    This effort is about the creation of a protocol for client
    applications to communicate with common name resolution services, as
    exemplified in both the browser enhancement and search site
    paradigms.  Although the protocol's primary function is resolution,
    it is also intended to address issues of internationalization and
    localization.  Name resolution services are not generic search
    services and thus do not need to provide complex Boolean query,
    relevance ranking or similar capabilities.  The protocol is a simple,
    minimal interoperable core.  Mechanisms for extension are provided,
    so that additional capabilities can be added.
 
 Table of Contents
 
    1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
    2.      Important Notes  . . . . . . . . . . . . . . . . . . . . .  5
    2.1     Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
    2.2     DTD is Definitive  . . . . . . . . . . . . . . . . . . . .  5
    2.3     Uniform Resource Identifiers . . . . . . . . . . . . . . .  5
    3.      Interaction Model  . . . . . . . . . . . . . . . . . . . .  5
    3.1     Services, Servers, Datasets and Referrals  . . . . . . . .  5
    3.2     Requests and Responses . . . . . . . . . . . . . . . . . .  6
    3.3     Transport Independence . . . . . . . . . . . . . . . . . .  6
    3.4     Character encoding . . . . . . . . . . . . . . . . . . . .  7
    3.5     Queries  . . . . . . . . . . . . . . . . . . . . . . . . .  7
    3.6     Hints  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
    4.      Object Model . . . . . . . . . . . . . . . . . . . . . . .  8
    4.1     Properties . . . . . . . . . . . . . . . . . . . . . . . .  9
    4.1.1   Core properties  . . . . . . . . . . . . . . . . . . . . .  9
    4.1.2   Abstract and custom properties . . . . . . . . . . . . . .  9
    4.1.3   Base properties  . . . . . . . . . . . . . . . . . . . . . 10
    4.1.4   Common name string encoding and equivalence rules  . . . . 11
    4.2     Objects  . . . . . . . . . . . . . . . . . . . . . . . . . 12
    4.2.1   Query  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
    4.2.1.1 Logical operations within a Query  . . . . . . . . . . . . 12
    4.2.2   Results  . . . . . . . . . . . . . . . . . . . . . . . . . 13
    4.2.2.1 ResourceDescriptor . . . . . . . . . . . . . . . . . . . . 13
    4.2.3   Service  . . . . . . . . . . . . . . . . . . . . . . . . . 14
    4.2.3.1 Datasets . . . . . . . . . . . . . . . . . . . . . . . . . 15
    4.2.3.2 Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 17
    4.2.4   Status Messages  . . . . . . . . . . . . . . . . . . . . . 19
    4.2.4.1 Status of CNRP, Not the Transport  . . . . . . . . . . . . 19
    4.2.4.2 Codes and Description  . . . . . . . . . . . . . . . . . . 19
    4.2.4.3 Status Codes . . . . . . . . . . . . . . . . . . . . . . . 20
    4.2.5   Referral . . . . . . . . . . . . . . . . . . . . . . . . . 21
    4.2.5.1 Loop Detection and Dataset Handling in Servers . . . . . . 22
    4.2.6   Discoverability: ServiceQuery and Schema . . . . . . . . . 24
 
 
 
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    5.      XML DTD for CNRP . . . . . . . . . . . . . . . . . . . . . 26
    6.      Examples . . . . . . . . . . . . . . . . . . . . . . . . . 28
    6.1     Service Description Request  . . . . . . . . . . . . . . . 28
    6.2     Sending A Query and Getting A Response . . . . . . . . . . 30
    7.      Transport  . . . . . . . . . . . . . . . . . . . . . . . . 31
    7.1     HTTP Transport . . . . . . . . . . . . . . . . . . . . . . 31
    7.2     SMTP Transport . . . . . . . . . . . . . . . . . . . . . . 32
    8.      Security Considerations  . . . . . . . . . . . . . . . . . 32
    9.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 32
            References . . . . . . . . . . . . . . . . . . . . . . . . 33
            Authors' Addresses . . . . . . . . . . . . . . . . . . . . 34
    A.      Appendix A: Well Known Property and Type Registration
            Templates  . . . . . . . . . . . . . . . . . . . . . . . . 35
    A.1     Properties . . . . . . . . . . . . . . . . . . . . . . . . 35
    A.2     Types  . . . . . . . . . . . . . . . . . . . . . . . . . . 35
    B.      Status Codes . . . . . . . . . . . . . . . . . . . . . . . 37
    B.1     Level 1 (Informative) Codes  . . . . . . . . . . . . . . . 37
    B.2     Level 2 (Success) Codes  . . . . . . . . . . . . . . . . . 37
    B.3     Level 3 (Partial Success) Codes  . . . . . . . . . . . . . 38
    B.4     Level 4 (Transient Failure) Codes  . . . . . . . . . . . . 39
    B.5     Level 5 (Permanent Failures) Codes . . . . . . . . . . . . 40
            Full Copyright Statement . . . . . . . . . . . . . . . . . 41
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 1. Introduction
 
    Services are arising that offer a mapping from common names to
    Internet resources (e.g., as identified by a URI).  These services
    often resolve common name categories such as company names, trade
    names, or common keywords.  Thus, such a resolution service may
    operate in one or a small number of categories or domains, or may
    expect the client to limit the resolution scope to a limited number
    of categories or domains.  For example, the phrase "Internet
    Engineering Task Force" is a common name in the "organization"
    category, as is "Moby Dick" in the book category.
 
    Two classes of clients of such services are being built, browser
    improvements and web accessible front-end services.  Browser
    enhancements modify the "open" or "address" field of a browser so
    that a common name can be entered instead of a URL.  Internet search
    sites integrate common name resolution services as a complement to
    search.  In both cases, these may be clients of back-end resolution
    services.  In the browser case, the browser must talk to a service
    that will resolve the common name.  The search sites are accessed via
    a browser.  In some cases, the search site may also be the back- end
    resolution service, but in others, the search site is a front-end to
    a collection of back-end services.
 
    This effort is about the creation of a protocol for client
    applications to communicate with common name resolution services, as
    exemplified in both the browser enhancement and search site
    paradigms.  Name resolution services are not generic search services
    and thus do not need to provide complex Boolean query, relevance
    ranking or similar capabilities.  The protocol is a simple, minimal
    interoperable core.  Mechanisms for extension are provided, so that
    additional capabilities can be added.
 
    Several other issues, while of importance to the deployment of common
    name resolution services, are outside of the resolution protocol
    itself and are not in the initial scope of the proposed effort.
    These include discovery and selection of resolution service
    providers, administration of resolution services, name registration,
    name ownership, and methods for creating, identifying or insuring
    unique common names.
 
    For the purposes of this document, a "common name" is a word or a
    phrase, without imposed syntactic structure, that may be associated
    with a resource.  These common names will be used primarily by
    humans, as opposed to machine agents.  A common name "resolution
    service" handles these associations between common names and data
    (resources, information about resources, pointers to locations, etc).
    A single common name may be associated with different data records,
 
 
 
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    and more than one resolution service is expected to exist.  Any
    common name may be used in any resolution service.
 
    Common names are not URIs (Uniform Resource Identifiers) in that they
    lack the syntactic structure imposed by URIs; furthermore, unlike
    URNs, there is no requirement of uniqueness or persistence of the
    association between a common name and a resource.  (Note:  common
    names may be expressed in a URI, the syntax for which is described in
    RFC XXXX [8].)
 
    This document will define a protocol for the parameterized resolution
    necessary to make common names useful.  "Resolution" is defined as
    the retrieval of data associated (a priori) with descriptors that
    match the input request.  "Parameterized" means the ability to have a
    multi-property descriptor.  Descriptors are not required to provide
    unique identification, therefore 0 or more records may be returned to
    meet a specific input query.
 
 2. Important Notes
 
 2.1 Terminology
 
       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
       NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
       "OPTIONAL" in this document are to be interpreted as described in
       RFC 2119 [6].
 
 
 2.2 DTD is Definitive
 
    The descriptive portions of this document contain pieces of XML that
    are *illustrative examples only*.  Section 5 of this document
    contains the XML DTD for CNRP, which is definitive.  If any
    discrepancies are found, the DTD wins.
 
 2.3 Uniform Resource Identifiers
 
    All URIs used within the CNRP protocol MUST adhere to the
    'absoluteURI' production found in the ABNF of [3].  CNRP does not
    define the semantics of a Base and therefore is not capable of
    expressing the 'URI-Reference' production.
 
 3. Interaction Model
 
 3.1 Services, Servers, Datasets and Referrals
 
    CNRP assumes a particular interaction model where a generalized
    "service" provides common name resolution at one or more actual
 
 
 
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    "servers".  If the data contained in all its servers is identical
    (mirrors), the service need not identify any particular subset of
    data.  If, however, the service provides different collections of
    data through different servers (e.g., subsets, specialized
    collections, etc), it SHOULD indicate what subsets of its data that
    each server offers.  This is done by using URIs to uniquely
    disambiguate one dataset from another.  If the service offers a copy
    of a collection of data on agreement with a foreign service,  the
    foreign service SHOULD provide a dataset URI to allow the collection
    to be identified as related to its own offerings.
 
    CNRP supports the concept of referrals.  This is where a server can
    know that another Service exists, within the same Service or
    elsewhere, that can provide further answers to a particular query but
    decides to forward that fact onto the client instead of chaining the
    query for the client.  A referral is sent along with the rest of the
    results from a server (if any).  Referrals to a service SHOULD
    indicate the particular dataseturi that triggered the referral, if it
    is known.  See Section 4.2.5 for details on referrals and loop
    detection.
 
 3.2 Requests and Responses
 
    The protocol consists of a simple request/response mechanism.  A
    client sends one of a few types of requests to a server which
    responds with the results of that request.  All requests and
    responses are encoded with XML [7] using the DTD found in Section 5.
    There are two types of requests.  One is a general query for a
    common-name.  The other is a request for an object that describes the
    service and its capabilities.  There is only one type of response
    which is a set of results.  Results can contain actual result items,
    referrals and/or status messages.
 
 3.3 Transport Independence
 
    CNRP is completely encapsulated within its XML definition, and is
    therefore transport-independent in its specification.  However,
    clients need to have a clearly defined means of bootstrapping a
    connection with a server.
 
    It is possible to define special-purpose applications that use CNRP
    but which never need the HTTP bootstrapping method outlined below;
    those applications MUST define how to find the appropriate
    server/port/protocol.  CNRP servers dedicated to those applications
    may provide service only on the ports/transport protocols defined by
    the application.
 
    All other (generic) CNRP clients and servers MUST support the HTTP
 
 
 
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    (Section 7.1) transport on the default CNRP port of 1096.
 
    Note that a particular service may choose to change to a different
    transport or port via statements within a CNRP service description
    request, but with initial contacts between a client and a server
    being over HTTP on port 1096.  For a short explanation of how CNRP
    employs HTTP, see Section 7.1 of this document.  If other transports
    are used they MUST be handled over a port other than the default CNRP
    port.
 
 3.4 Character encoding
 
    To guarantee interoperability, the following provisions apply:
 
    o  XML queries and responses MUST be encoded as UTF-8.
 
       Note: As in any XML document, numeric character references may be
       used.
 
    o  The encoding of characters in the CNRP URI is based on UTF-8; for
       details, please see [8]
 
    Any interfaces electing to present/accept protocol elements in other
    representations are responsible for accurate transcoding for use in
    CNRP protocol elements, per the above provisions.
 
 3.5 Queries
 
    Queries are sent by the client to the server.  There are two types of
    queries.
 
    1.  A `special' initial query that establishes the schema for a
        particular CNRP database and communicates that to the client.
        The CNRP client will send this query, and in turn receive an XML
        document defining the query properties that the database
        supports.  (In CNRP, XML [7] is used to define and express all
        objects.) This query is called the 'servicequery' in the DTD.  In
        the case where a client does not know anything about the Service,
        the client MAY assume that it can at least issue the request via
        HTTP.
 
    2.  A `standard' query, which is the submission of the CNRP search
        string to the database.  The query will conform to the schema
        that MAY have been previously retrieved from the service.
 
    There will be a set of query properties, listed below, treated as
    hints by the server.  Note:  a CNRP database will accept any
    correctly encoded CNRP query property; the extent to which a query
 
 
 
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    result is responsive to those properties is a service differentiator.
    The base properties that are always supported are common name,
    language, geography, category, and range (start and length of the
    result set).  CNRP allows database service providers to create unique
    data types and expose them to any CNRP client via the CNRP schema XML
    documents.
 
 3.6 Hints
 
    A hint is an assertion by the user about himself, herself or itself
    and the context in which he/she/it is operating.  There is no data
    type `hint'; a hint is expressed within the structure of the query
    itself and is limited or enabled by the richness of the defined query
    namespace.  In effect, a query and any property within it is a hint.
 
    For example, the "language" property can be given as a hint in a
    query; this may be used to order search results.  If one wants
    results first in US English followed by European French and finally
    South American Spanish, the following can be included in the query:
 
 
       <property name="language" type="rfc1766">en-US</property>
 
       <property name="language" type="rfc1766">fr-FR</property>
 
       <property name="language" type="rfc1766">sp-MX</property>
 
    Note that the property statements say nothing about whether the
    language is primary, secondary,etc.  In this example the ordering of
    the statement controls that--the first statement, being first, means
    that US English is the primary language.  The second statement
    specifies the second region/language, and so on.  *But this is only
    an example.*  The extent to which hints are supported (or not) is a
    service differentiator.
 
    The fact that a hint exists does not mean that a CNRP database must
    respond to it.  This best-effort approach is similar to relevance
    ranking in a search engine (high precision, low recall); hints are
    similar to a search engine's selection criteria.  CNRP services will
    attempt to return the results "closest" to the selection criteria.
    This is quite different from a SQL database approach where a SQL
    query returns the entire results set and each result in the set must
    match all the requirements expressed by the qualifier (the SQL WHERE
    clause).
 
 4. Object Model
 
 
 
 
 
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 4.1 Properties
 
    In CNRP, objects are property lists.  A property is a named
    attribute.  A property also has a well-defined type.  Some properties
    can be part of the query or the results list or both.  For
    simplicity, CNRP is limiting property values to string values.
 
 4.1.1 Core properties
 
    CNRP introduces a set of core properties.  Core properties are the
    minimal set of properties that all CNRP services MUST support in
    order to reach CNRP compliance.  Hence, the core properties define
    the level of interoperability between all CNRP services.  The core
    properties are:
 
    1.  CommonName: the common name associated with a resource.
 
    2.  ID: an opaque string that serves as a unique identifier for a
        result from a Service (typically a database ID).  The ID is not
        globally unique, nor necessarily persistent (e.g., between
        queries at a given Service)
 
    3.  resourceURI: An 'absoluteURI' as defined in the collected ABNF
        found in RFC 2396 [3].
 
    4.  description: A free text description of the resource.
 
 
 4.1.2 Abstract and custom properties
 
    In addition to core properties, CNRP introduces the notion of
    abstract properties.  The abstract property element provides schema
    extensibility beyond the core properties.  The notion of abstract
    property is extremely important in CNRP since it enables a wider
    range of CNRP based services than those based on the core properties.
 
    To create concrete custom properties, a CNRP service must define a
    property name and a property type.  Therefore, there are really two
    ways to create a custom property.  The first way is to create a new
    property name and define at least one type for it.  Another way is to
    extend an existing property by defining a new type.  The "geography"
    property discussed in the next section is an example of a multi-type
    property.  Note that a type is only applicable to the property it is
    defined for.  If a new property is defined, a new type MUST be
    defined even though the value set for that type may be identical to
    an existing type for an existing property.  In other words, types are
    scoped to a given property.  Custom properties MUST be registered
    with IANA.  Details about the registration process for new properties
 
 
 
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    can be found in Section 9.
 
    For example, let us assume that a CNRP service specialized on online
    books would like to introduce the ISBN property of type "number".
    This property would encapsulate the ISBN number of the book online
    and would have he following XML representation:
 
       <property name="isbn" type="number">92347231</property>
 
 
 4.1.3 Base properties
 
    Illustrating the use of abstract property to extend the core schema,
    CNRP also defines a set of custom properties called base properties.
    In order to keep the requirements extremely simple, these properties
    are not mandatory to implement to reach CNRP compliance.  Although,
    these properties are not required, it is expected that many services,
    especially large ones, will implement them.  An equally important
    goal for introducing additional properties is to provide a results
    filtering mechanism.  This is a requirement for large namespaces that
    contain several million names.
 
    The base properties and their types are defined in Appendix A but
    listed here for clarity:
 
    o  Language:
       The language associated with a resource.  The default type of this
       property is 'RFC1766' and the vocabulary is drawn from the list of
       languages in RFC 1766 [4].  If RFC 1766 is updated then the values
       listed in the updated version are also valid for this type.
 
    o  Geography:
       The geographical region or location associated with a resource.
       Some of the possible types are listed below.  See Appendix A for a
       complete list of types specified by this document.
 
       *  'freeform': a free form expression for a geographical location
          (e.g.  "palo alto in california").
 
       *  'ISO3166-1': geographical region expressed using a standard
          country code as defined by ISO3166-1 (e.g.  "US").
 
       *  'ISO3166-2':  value = a geographical region expressed using a
          standard region and country codes as defined by ISO3166-2 (e.g.
          "US-CA").
 
       *  'lat-long': the latitude and longitude of a geographical
          location
 
 
 
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    o  Category:
       The category associated with a resource.  There are large numbers
       of possible types for this property.  Two possible ones are:
 
       1.  'freeform': a free form expression for a category (e.g.
           "movies").
 
       2.  'NAICS': The North American Industry Code System.
 
    o  Range:
       The range is a results set control property.  The range property
       is used to specify the starting point and the length of a results
       set (e.g.  I want 5 records starting at the 10th record).  It
       should only ever have one type but, in the interest of
       extensibility and consistency, others can be created if there is a
       need.  The default type is 'start-length' which takes the form of
       two integers separated by a dash.  The first integer is the
       starting number and the second is the number of values to include.
 
    o  Dataseturi: An absoluteURI (as defined in [3] that identifies a
       defined set of Common Names and associated data.
 
    NOTE: For many properties the default "type" is "freeform".  The free
    form type value is important because it allows very simple user
    interface where the user can enter a value in a text field.  It is up
    to the service to interpret the value correctly and take advantage of
    it to increase the relevance of results (using specialized
    dictionaries for instance).
 
 4.1.4 Common name string encoding and equivalence rules
 
    CNRP specifies that common name strings should be encoded using UTF-
    8.  CNRP does not specify any string equivalence rules for matching a
    common name in the query against a common name of a Resource.  String
    equivalence rules are language and service dependent.  They are
    specific to relevance ranking algorithms, hence treated as CNRP
    services.  Consequently, string equivalence rules are not part of the
    CNRP protocol specification.  For example, the query member:
 
       <commonname>bmw</commonname>
 
    Should be read as a selection criterion for a resource with a common
    name LIKE (similar to) the string "bmw" where the exact  definition
    of the LIKE operator is intuitive, yet specific to the queried CNRP
    service.
 
    It is also important to note that XML treats whitespace as a special
    case in many situations.  In some cases it collapses whitespace into
 
 
 
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    a single space.  Both client and server Implementors are warned to
    reference the XML standard for the various ramifications of using
    whitespace in queries and/or results.
 
 4.2 Objects
 
 4.2.1 Query
 
    The Query object encapsulates all the query components such as
    CommonName, ID, and any properties.  A Query cannot be empty.  A
    Query must contain either one and only one common name, or one and
    only one ID.  A Query can also contain the custom properties defined
    by a specific CNRP service.
 
    For example, a query for the first 5 resources whose common name is
    like "bmw" would be expressed as:
 
    <query>
            <commonname>bmw</commonname>
            <property name="range" type="start-length">1-5</property>
    </query>
 
 
 4.2.1.1 Logical operations within a Query
 
    The Query syntax is extremely simple.  CNRP does not extensively
    support Boolean logic operator such as OR, AND or NOT.  However,
    there exist two implicit logical operations that can be expressed
    through the Query object and its properties.  First, a query with
    multiple property-value pairs implicitly expresses an AND operation
    on the query terms.  For instance, the CNRP query to request all the
    resources whose common name is like "bmw", AND whose language is
    "German" can be expressed as:
 
    <query>
         <commonname>bmw</commonname>
         <property name="language" type="rfc1766">
            de-DE
         </property>
    </query>
 
    Note however, that because the server is only trying to best match
    the Query criteria, there is no guarantee that all or any of the
    resources in the results match both requirements.
 
    In addition, CNRP allows the client to express a logical OR by
    specifying multiple values for the same property within the Query.
    For example, the logical expression:
 
 
 
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       property = value1 OR property = value2 OR property = valueN
 
    Will be expressed as:
 
    <property>value1</property>
    <property>value2</property>
    <property>valueN</property>
 
    So if there are different properties expressed, CNRP ANDs them; if
    there are multiples instances of the same property expressed, CNRP
    ORs them.
 
    It is important to underline that this form is only applicable to
    properties (with the exception of the CommonName itself which, even
    though it is a property, is the entire point of the query).  In
    particular, logical OR operations on the common name are not
    supported.  Note that the ordering or the property-value pairs in the
    query implies a precedence.  As a consequence, CNRP also introduces
    one special string value: "*".  Not surprisingly, "*" means all
    admissible values for the typed property.  For example, the following
    query requests all the resources whose common name is like BMW and
    whose language is preferably in German or French or any other
    language.
 
    <query>
         <commonname>bmw</commonname>
         <property name="language" type="rfc1766">de-DE</property>
         <property name="language" type="rfc1766">fr-FR</property>
         <property name="language" type="rfc1766">*</property>
    </query>
 
 
 4.2.2 Results
 
    The results object is a container for CNRP results.  The type of
    objects contained in Results can be: ResourceDescriptor, Error,
    Referral and Schema.  Results from a CNRP service are ordered by
    decreasing relevance.  When the results set contains results from
    multiple CNRP services, the results can no longer be ordered (since
    relevance ranking is specific to a given service).  In that case,
    however, note that results originating from the same service remain
    ordered.
 
 4.2.2.1 ResourceDescriptor
 
    The ResourceDescriptor object describes an Internet resource (e.g.  a
    Web page, a person, any object identified by a URI).  Therefore, the
    ResourceDescriptor MUST always include the resourceURI property.  The
 
 
 
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    ResourceDescriptor can also contain the commonname, URI, ID (the ID
    of this entry in the service's database), description, language,
    geography, and category of the resource.  A ResourceDescriptor can
    also be augmented using custom properties and can reference a service
    object to indicate its origin (using the serviceRef element).  As
    with referrals, a resourcedescriptor block can also contain an ID
    attribute that is used by a status message to refer to a particular
    resourcedescriptor.  Be careful not to confuse this ID with the id
    tag itself which refers to the database id of the actual database
    entry.
 
 
    <results>
         <service id="i0">
              <serviceuri>http://cnrp.bar.com/</serviceuri>
         </service>
         <resourcedescriptor id="i1">
              <commonname>bmw</commonname>
              <id>foo.com:234364</id>
              <resourceuri>http://www.bmw.de/</resourceuri>
              <serviceref ref="i0" />
              <description>BMW Motorcycles, International</description>
              <property name="language" type="rfc1766">de-DE</property>
         </resourcedescriptor>
         <referral>
              <serviceref ref="i0" />
         </referral>
    </results>
 
 
 
 4.2.3 Service
 
    The Service object provides an encapsulation of an instance of a CNRP
    service.  A service is uniquely identified through the serviceuri tag
    which MUST be included in the Service object.  A Service object MAY
    include a a brief textual description of the service.  It MAY include
    datasets, servers and custom properties.
 
    <service>
         <serviceuri>http://cnrp.foo.com</serviceuri>
         <description>foo.com is a CNRP service specialized on cocktail
            recipes</description>
    </service>
 
    The service object MAY also be extended by including existing
    properties to further describe the service.  For instance, a service
    that focuses on French companies could be expressed as:
 
 
 
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    <service>
         <serviceuri>http://cnrp.foo.com</serviceuri>
         <property name="category" type="freeform">companies</property>
         <property name="geography" type="ISO3166-1">FR</property>
    </service>
 
 
 4.2.3.1 Datasets
 
    The dataset object represents a set of CN-to-URI mappings.  For
    example, the database of AOL keywords and their URIs constitute a
    dataset.  The dataset object allows a CNRP implementation to uniquely
    identify the database(s) of mappings that it resolves.  In that
    respect, the notion of dataset allows a separation between resolution
    and data, providing the mechanism for a CNRP service to resolve
    common-names on behalf of another CNRP service or even multiple
    services.  Conversely, the same dataset can be served by two distinct
    CNRP services.  Since a CNRP service can resolve names within one or
    more datasets, the service object can contain one or more dataset
    objects (zero if the dataset is not formally declared).
 
    Within the service object, a dataset is uniquely defined using the
    dataseturi property.  Other properties, such as language and
    description, can describe the dataset further.  Like the service
    object, the dataset object has an ID attribute associated with it
    that is unique within a particular XML message.  Like the service
    object's ID attribute, this ID is used by resourcedescriptors and
    referrals to specify which service and/or dataset they came from or
    are referring to.
 
    Any service can be said to have a 'default dataset' which is the
    dataset that considered to have been used if a server simply responds
    to a client's query that didn't contain a dataset.  The 'default
    dataset' can also be said to be the only dataset that is used by
    Services that don't support datasets at all.  This concept is useful
    for clients that intend on doing rigorous loop detection by way of
    keeping a list of visited service/dataset nodes.
 
    This example illustrates how the service object would look as it
    defines two datasets:
 
 
 
 
 
 
 
 
 
 
 
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    <service id="i0">
        <serviceuri>http://acmecorp.com</serviceuri>
        <dataset id="i1">
            <property name="dataseturi">urn:oid:1.2.3.4.666.5.4.3.1</property>
            <property name="language">en-us</property>
            <property name="language">en-gb</property>
        </dataset>
        <dataset id="i2">
            <property name="dataseturi">urn:oid:1.2.3.4.666.10.9.8.7.6</property>
            <property name="language">fr</property>
        </dataset>
    </service>
 
    The dataseturi property can also be used within the query as a hint
    to the service for the dataset within which the commonname should be
    resolved:
 
 
    <query>
       <commonname>toys r us</commonname>
       <property name="dataseturi">urn:oid:1.2.3.4.666.5.4.3.1</property>
    </query>
 
    It is important to note that resolution rules (i.e.  string
    equivalence, relevance ranking, etc) are likely to be dataset
    specific.  This is true even if the resolution is provided by the
    same service.
 
    Another use of the dataseturi property is in a referral.  In that
    case, the datasetref tag is used to pinpoint a specific dataset
    within the service.
 
 
    <referral>
       <serviceref ref="i0" /><datasetref ref="i1" />
    </referral>
 
    While the concept of datasets is important for services wishing to
    make their data available via other services, it is important to
    remember that the declaration and use of datasets is completely
    optional.  Compliance with the CNRP protocol does not require a
    service object to define or reference any dataset object.  The only
    requirement for compliance is that a client and/or server know the
    format of the particular XML tags and deal with them syntactically.
    If it chooses to ignore them then this is well within its rights.
 
 
 
 
 
 
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 4.2.3.2 Servers
 
    The service object  also encapsulates a list of server objects.  The
    server object is used to describe a CNRP server or set of servers.  A
    server is identified through its serveruri.  The URI used to identify
    a server is not a CNRP URI [8] but instead is a URI of the scheme
    used as the CNRP transport mechanism.  I.e.  for a CNRP server that
    will communicate via the HTTP protocol to the host foo.com on port
    6543, the serveruri would be http://foo.com:6543.  If some other
    information is required in order for the correct transport to be
    used, then that information can be communicated via other properties.
    Note that a Service MUST have at least one Server that responds on
    the default CNRP port in order for a client to get the initial
    Service object.
 
    A server can serve one or more datasets declared by its service.  The
    served databases are specified using the dataseturi property.  As for
    other objects, a server can be further described using descriptive
    properties such as geography and description.  The following XML
    completes the service definition from the previous example by
    defining two CNRP servers.  One server is located in the US and the
    other is located in France.  The US server is specialized and only
    serves the French dataset.
 
      <servers>
         <server>
            <serveruri>cnrp://router.us.widgetco.com:4321</serveruri>
            <property name="geography" type="ISO3166-1">US</property>
         </server>
         <server>
            <serveruri>cnrp://router.fr.acmeco.com:4321</serveruri>
            <property name="geography" type="ISO3166-1">FR</property>
         </server>
      </servers>
 
    As we will see in a following section, the Service object can contain
    Schema objects.  These Schema objects fully describe the query and
    response interfaces implemented by a CNRP service.  In that regard,
    the Service object is essential to discoverability.  It constitutes
    the main entry point for a CNRP client to dynamically discover the
    capabilities of a resolution service.  For that purpose, the Service
    object can be returned as part of the response to any resolution
    query.  Furthermore, the Service object is the dedicated response to
    the specialized servicequery (see Section 4.2.6).
 
    Another use of Service is for other objects to indicate their CNRP
    service of origin.  System messages, referrals and
    resourcedescriptors can include a reference to their Service object.
 
 
 
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    For example, imagine a CNRP service that acts as a proxy for multiple
    CNRP services.  For example, it is a requirement that CNRP allows
    aggregation of results from different sources.  Consider one such
    CNRP service that acts as a proxy for multiple CNRP services.  In
    this mode, the proxy service contacts each CNRP sub-service in
    parallel or serially.  Then, the proxy combines the individual result
    sets into a unique response returned to the CNRP client.  Since the
    aggregate result set contains resourcedescriptors from different
    services, the proxy adds a servicereference tag within each
    individual result to indicate their service of origin.  In the event
    one of the referred services resolves names within multiple datasets,
    it is possible for these objects to refer to a specific dataset
    within the service by using the datasetref tag.  This example is of a
    hybrid result set with resourcedescriptors referencing their service
    and dataset of origin:
 
    <?xml version="1.0"?>
    <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN"
        "http://ietf.org/dtd/cnrp-1.0.dtd">
    <cnrp>
         <results>
              <service id="i0">
                   <serviceuri>http://acmecorp.com</serviceuri>
                   <dataset id="i1">
                      <property name="dataseturi">
                   urn:oid:1.2.3.4.666.5.4.3.1
                      </property>
                   </dataset>
                   <dataset id="i2">
                      <property name="dataseturi">
                       urn:oid:1.2.3.4.666.10.9.8.7.6
                      </property>
                   </dataset>
              </service>
              <service id="i3">
                 <serviceuri>http://serverfarm.acmecorp.com</serviceuri>
              </service>
              <service id="i4">
                  <serviceuri>http://servers.acmecorp.co.uk</serviceuri>
                  <dataset id="i5">
                      <property name="dataseturi">
                        urn:oid:1.2.3.4.666.5.4.3.1
                      </property>
                  </dataset>
              </service>
              <resourcedescriptor>
                        <commonname>Fidonet</commonname>
                        <id>1333459455</id>
 
 
 
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                        <resourceuri>http://www.fidonet.ca</resourceuri>
                        <serviceref ref="i0" /><datasetref ref="i1" />
                        <description>This is ye olde Canadian
                         Fidonet</description>
              </resourcedescriptor>
              <resourcedescriptor>
                        <commonname>Fidonet</commonname>
                        <id>1333459455</id>
                        <resourceuri>http://host:port/bla</resourceuri>
                        <serviceref ref="i3" />
                        <description>An old Fidonet node</description>
              </resourcedescriptor>
              <referral>
                  <serviceref ref="i0" /><datasetref ref="i2" />
              </referral>
         </results>
    </cnrp>
 
 
 4.2.4 Status Messages
 
 4.2.4.1 Status of CNRP, Not the Transport
 
    The status messages defined here are only applicable to operations
    defined by CNRP itself.  If some feature or operation is defined by
    the transport (security via HTTP, mail failure via SMTP, etc) then
    any status messages about that operation MUST be sent in accordance
    with that transport's reporting mechanism and not via CNRP.
 
 4.2.4.2 Codes and Description
 
    A Status object indicates a message to the client in the results set.
    The object encapsulates two values: a status code and a description.
    The description can contain a textual description of the status being
    communicated.  In many cases, additional diagnostic information can
    also be included.  No attempt is made to standardize the description
    of a given status code since the only programmatic element that
    matters is the actual code.
 
    A status message can also specify which other CNRP element it refers
    to by including a reference to the ID of the element in question.
    For example, if a Service block has an ID of "i2" and a status
    message refers to that block then it can put that ID in its ref
    attribute.
 
 
 
 
 
 
 
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             <status code="x.y.z" ref="i2">
                  The CNRP foo.com database is temporarily unreachable
             </status>
 
 
 4.2.4.3 Status Codes
 
    The organization of status codes is taken from RFC 1893 [9] which
    structures its codes in the form of x.yyy.zzz.  Taken from RFC 1893
    is the ABNF for the codes:
 
              status-code = class "." subject "." detail
              class = "2"/"3"/"4"/"5"
              subject = 1*3digit
              detail = 1*3digit
 
    The top level codes denote levels of severity of the status:
 
 
    o  1.X.X Informational
 
 
       *  The information conveyed by the code has no bearing or
          indication of the success or failure of any request.  It is
          strictly for informational purposes only.
 
 
    o  2.X.X Success
 
 
       *  The request was processed and results were returned.  In most
          cases this status class won't be sent since actual results
          themselves denote success.  In other cases results were
          returned but some information needs to be returned to the
          client.
 
 
    o  3.X.X Partial Success
 
 
       *  The request was processed and results were returned.  In this
          case though, some values sent with the request were either
          invalid or ignored but in a way that the server still considers
          the response to be a successful one and not indicative of any
          true error condition.
 
 
    o  4.X.X Transient Failure
 
 
 
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       *  The request was valid as sent, but some temporary event
          prevents the successful completion of the request and/or
          sending of the results.  Sending in the future may be possible.
 
 
    o  5.X.X Permanent Failure
 
 
       *  A permanent failure is one which is not likely to be resolved
          by re-sending the request in its current form.  Some change to
          the request or the destination must be made for successful
          request.
 
 
    The second level codes denote the subject of the status messages.
    This value applies to each of the five classifications.  The subject
    sub-code, if recognized, must be reported even if the additional
    detail provided by the detail sub-code is not recognized.  The
    enumerated values for the subject sub-code are:
 
 
    o  X.0.X Other or Undefined Status
 
 
       *  No specific information is available about what subject class
          this message belongs to
 
 
    o  X.1.X Query Related
 
 
       *  Any status related to some specific way in which the query was
          encoded or its values with the exception of properties.
 
 
    o  X.2.X Service Related
 
 
       *  Any status related to the service in which this server is
          cooperating in providing.
 
    Appendix B contains a list of all predefined status codes
 
 4.2.5 Referral
 
    A Referral object in the results set is a place holder for un-fetched
    results from a different service and possibly dataset.  Referrals
    typically occur when a CNRP server knows of another service capable
    of providing relevant results for the query and wants to notify the
 
 
 
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    client about this possibility.  The client can decide whether it
    wants to follow the referral and resolve the extra results by
    contacting the referred-to service using the information contained
    within the Referral object (a Service object and possible
    properties).  The Referral is a simple mechanism to enable
    hierarchical resolution as well as to join multiple resolution
    services together.
 
    <results>
         <service id="i0">
              <serviceuri>http://cnrp.bar.com/</serviceuri>
              <dataset id="i1">
                 <property name="dataseturi">
                   urn:oid:1.3.6.1.4.1.782.1
                 </property>
              </dataset>
              <dataset id="i2">
                 <property name="dataseturi">
                   urn:oid:1.3.6.1.4.1.782.2
                 </property>
              </dataset>
         </service>
         <resourcedescriptor>
              <commonname>bmw</commonname>
              <id>foo.com:234364</id>
              <resourceuri>http://www.bmw.de/</resourceuri>
              <serviceref ref="i0" /><datasetref ref="i1" />
              <description>BMW Motorcycles, International</description>
              <property name="language" type="iso646">de-DE</property>
         </resourcedescriptor>
         <referral>
              <serviceref ref="i0" /><datasetref ref="i2" />
         </referral>
    </results>
 
    Like other CNRP objects, a referral can be further described using
    custom properties.  Like a resourcedescriptor, a referral can have an
    ID attribute that is used by a status message to talk about a
    particular referral block.
 
 4.2.5.1 Loop Detection and Dataset Handling in Servers
 
    Referrals in CNRP can be handled in three ways:
 
    o  application specific
 
    o  as hints only
 
 
 
 
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    o  rigorous loop detection
 
    In the first two cases the behavior of the client when it receives a
    referral is not defined in this memo.  The client can chase the
    referral in such a way as to treat it as a hint only.  In this case
    datasets may or may not be handled.  Loop detection can be nothing
    more than "Have I talked to this hostname before?" or "Stop after the
    3rd referral".  These two cases are most likely to apply to simple or
    constrained implementations where the clients and servers have some a
    priori knowledge of their capabilities.  Without such knowledge there
    is too much ambiguity vis-a-vis services and datasets for clients to
    do reliable loop detection.
 
    The last case is where the client expects to talk to mutliple servers
    that may know nothing about each other.  This case expresses the
    basic semantics of what a server should tell a client if it
    understands datasets or referrals.  Since a referral specifies the
    exact dataset to which it is referring, a node in the list of visited
    nodes is made up of a serviceuri and a dataseturi.  Both of these
    values need to be considered during loop detection.  In the case
    where a service does not support datasets, the visited node is made
    up of the service and the 'default dataset'.
 
    The major thing to remember when doing loop detection across servers
    is that some servers may not understand datasets at all while others
    specifically rely on them.  To help determine how loop detection
    nodes should be marked, three specific status messages have been
    defined:
 
    The 3.1.3 (Datasets not supported) status message is used to denote
    that the server does not support datasets at all.  It is sent in
    response to a query containing datasets.  The client should consider
    that the server ignored the datasets and the client should consider
    this node to have been visited for all possible datasets (including
    the 'default' dataset).
 
    The 3.1.4 (First dataset only supported) status message is used by a
    server to indicate the situation where a client has included several
    dataseturis in its query and the server can only support one at a
    time.  In this case the server is explicitly stating that it used the
    first dataseturi only.  The client should consider that only the
    first dataseturi specified was processed correctly.  The client
    should consider that the remaining datasets in the query were ignored
    completely.  They would need to be sent individually as referrals if
    the client really cares about those results.  Only the first
    serviceuri/dataseturi pair should be marked as visited.
 
    The 3.1.5 (This dataset not supported) status message is used to
 
 
 
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    indicate that a specific dataseturi sent in a query by a client is
    not supported by the server.  This serviceuri/dataseturi pair should
    be considered as visited by the client.  If this message is sent in
    reply to a query specifying multiple datasets, the client should
    behave the same as if it recieved the 3.1.3 message from above.  It
    should be considered bad form for a server to send this status
    message back in response to a query with multiple datasets because it
    is ambigious.
 
    While there is no exact algorithm for loop detection that clients are
    encouraged to support, these status messages can be used by the
    server to be clear about what Services and Datasets it considers to
    have been queried.  It is up to the client to decide what to do with
    these messages and how closely it attempts to do loop detection.
 
 4.2.6 Discoverability: ServiceQuery and Schema
 
    A subclass of Query, the ServiceQuery object supports the dynamic
    discovery of a specific CNRP service's characteristics.  Note that
    CNRP compliance does not require that a service fully implements
    discoverability.  In particular, returning the Service object with
    its serviceuri constitutes a minimal yet sufficient compliant
    implementation.  Nevertheless, we expect that advanced CNRP services
    will choose to return a full description of their supported
    interfaces.
 
    The complete response to a servicequery returns the Service object
    described in section 5.3.2 with the following schema information.
 
    1.  The base and custom properties used by the CNRP service (Property
        schema),
 
    2.  The properties used to describe the Service object (Service
        schema)
 
    3.  The properties that belong to the query interface (Query schema)
 
    4.  The properties that belong to a resource within the results
        (Resource schema).
 
    These leads to the following new object definitions:
 
    o  propertyschema -- A property schema describes all the custom
       properties that are part of the service.
 
    o  propertydeclaration -- A property declaration describes a base or
       custom property used by the CNRP service.  A property declaration
       has a name and a type (the name and the type of the property that
 
 
 
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       it refers to).  Note that as part of the property schema, one MUST
       declare both existing and newly defined properties.
 
    o  propertyreference -- A property reference is a reference to a
       property declaration so that a given schema (a service, query or
       resource schema) can declare the property within its interface.
       Note that a property reference specify whether the use of the
       property is required or optional only.
 
    o  serviceschema -- The service schema defines the properties used to
       describe the service.
 
    o  queryschema -- A query schema describes the structure of a query
       handled by the CNRP service.  The properties referred within the
       query schema are part of the query interface of the resolution
       service.
 
    o  resourcedescriptorschema -- A ResourceDescriptor schema describes
       the resource returned as a result by the CNRP service.
 
    For example, a CNRP query to discover a service's capabilities will
    be in the form:
 
    <cnrp> <servicequery/> </cnrp>
 
 
    And for a CNRP service for cocktail recipes in French, the
    corresponding response would be:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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    <service>
         <serviceuri>http://cnrp.recipe.com</serviceuri>
         <propertyschema>
            <propertydeclaration id="i1">
                  <propertyname>language</propertyname>
                  <propertytype>rfc1766</propertytype>
            </propertydeclaration>
            <propertydeclaration id="i2">
                  <propertyname>cocktailrecipe</propertyname>
                  <propertytype>freeform</propertytype>
            </propertydeclaration>
         </propertyschema>
         <queryschema>
              <propertyreference required="yes" ref="i1"/>
         </queryschema>
         <resourcedescriptorschema>
              <propertyreference required="yes" ref="i1"/>
              <propertyreference required="yes" ref="i2"/>
         </resourcedescriptorschema>
    </service>
 
    This response stipulates that the service accepts the property
    language as part of the query interface and returns
    resourcedescriptors that contain both the language and cocktailRecipe
    properties.
 
 5. XML DTD for CNRP
 
 
    <!-- The document tag -->
    <!ELEMENT cnrp (query|results|servicequery)>
 
 
    <!-- Used to request a Service object -->
    <!ELEMENT servicequery EMPTY>
 
 
    <!-- A query can either request a schema, a specific record by id,  -->
    <!-- or a common-name with a set of properties (or assertions) about-->
    <!-- the entity doing the query.                                    -->
    <!ELEMENT query (id|(commonname,property*))>
    <!ELEMENT id (#PCDATA)>
 
 
    <!ELEMENT commonname (#PCDATA)>
    <!-- NOTE: CNRP defines several well known properties and types.     -->
    <!-- See Appendix A for details.                                     -->
    <!ELEMENT property (#PCDATA)>
 
 
 
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    <!-- The name of the property -->
    <!ATTLIST property name CDATA #REQUIRED>
    <!-- The type of the property -->
    <!ATTLIST property type CDATA "freeform">
 
    <!ELEMENT results (status? |
                       ( service+,
                        ( status  | resourcedescriptor | referral )*
                   )*
                  )>
 
    <!ELEMENT resourcedescriptor (commonname,id,resourceuri,
        serviceref, datasetref?,
        description,
        property*)>
    <!ATTLIST resourcedescriptor id ID #IMPLIED>
 
 
    <!-- The entire point of all this... -->
    <!ELEMENT resourceuri (#PCDATA)>
    <!ELEMENT description (#PCDATA)>
 
    <!ELEMENT referral (serviceref, datasetref?)>
    <!ATTLIST referral id ID #IMPLIED>
 
    <!ELEMENT status (#PCDATA)>
    <!ATTLIST status code CDATA #REQUIRED>
    <!ATTLIST status ref IDREF #IMPLIED>
 
    <!-- serviceRef is used to point to one of a set of provided service -->
    <!-- objects. This is so that a resource can point to which service  -->
    <!-- it came from. We could include the entire service object but    -->
    <!-- then we would be repeating large amounts of information.        -->
 
    <!ELEMENT serviceref EMPTY>
    <!ATTLIST serviceref ref IDREF #IMPLIED>
 
    <!ELEMENT service (serviceuri, dataset*,
       servers?,
       description?,
       property*,propertyschema?,queryschema?,resourcedescriptorschema?,
       serviceschema?)>
    <!-- The time to live of the schema in seconds since it was retrieved -->
    <!ATTLIST service ttl CDATA "0">
    <!ATTLIST service id ID #IMPLIED>
    <!ELEMENT serviceuri (#PCDATA)>
    <!ELEMENT servers (server+)>
    <!ELEMENT server (serveruri, property*)>
 
 
 
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    <!ELEMENT serveruri (#PCDATA)>
 
    <!ELEMENT dataset (property*)>
    <!ATTLIST dataset id ID #IMPLIED>
 
    <!ELEMENT datasetref EMPTY>
    <!ATTLIST datasetref ref IDREF #IMPLIED>
 
    <!ELEMENT propertyschema (propertydeclaration*)>
    <!ELEMENT propertydeclaration (propertyname, propertytype*)>
    <!ATTLIST propertydeclaration id ID #IMPLIED>
 
 
    <!ELEMENT propertyname (#PCDATA)>
    <!ELEMENT propertytype (#PCDATA)>
    <!-- This specifies if the type is meant to be the default type. -->
    <!-- This is usually reserved for "freeform".                    -->
    <!ATTLIST propertytype default (no|yes) "no">
 
 
    <!-- The properties you can use in a query -->
    <!ELEMENT queryschema (propertyreference*)>
 
 
    <!-- The properties you can expect to see in an Resource -->
    <!ELEMENT resourcedescriptorschema (propertyreference*)>
 
 
    <!-- The properties you can expect to find in a Service definition -->
    <!ELEMENT serviceschema (propertyreference*)>
 
 
    <!ELEMENT propertyreference EMPTY>
    <!-- This specifies if a property is required as part of the query. -->
    <!ATTLIST propertyreference ref IDREF #REQUIRED>
    <!ATTLIST propertyreference required (no|yes) "no">
 
 
 
 6. Examples
 
 6.1 Service Description Request
 
    This is what the client sends when it is requesting a servers schema.
 
 
 
 
 
 
 
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    <?xml version="1.0"?>
    <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN"
     "http://ietf.org/dtd/cnrp-1.0.dtd">
    <cnrp>
         <servicequery />
    </cnrp>
 
 
    This is the result.  Notice how the Service tag is used to allow the
    service to describe itself in its own terms.
 
 
    <?xml version="1.0"?>
    <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN"
     "http://ietf.org/dtd/cnrp-1.0.dtd">
    <cnrp>
         <results>
         <service ttl="43200">
              <serviceuri>urn:foo:bar</serviceuri>
              <servers>
              <server>
              <serveruri>http://host1.acmecorp.com:4321/foo?</serveruri>
              </server>
              <server>
              <serveruri>smtp://host2.acmecorp.com:4321/foo?</serveruri>
              </server>
              </servers>
              <description>This is the AcmeCorp CNRP Service</description>
              <!-- This property means that AcmeCorp specializes in
                   tradename services -->
              <property name="category" type="naics">544554</property>
              <property name="BannerAdServer" type="uri">
                  http://adserver.acmecorp.com/
              </property>
              <propertyschema>
                   <propertydeclaration id="i1">
                        <propertyname>workgroupID</propertyname>
                        <propertytype default="yes">freeform</propertytype>
                        <propertytype default="no">domainname</propertytype>
                        </propertydeclaration>
                        <propertydeclaration id="i2">
                        <propertyname>BannerAdServer</propertyname>
                        <propertytype default="yes">URI</propertytype>
                   </propertydeclaration>
              </propertyschema>
              <queryschema>
                   <propertyreference ref="i1" required="yes" />
              </queryschema>
 
 
 
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              <resourcedescriptorschema>
                   <propertyreference ref="i1" required="yes" />
              </resourcedescriptorschema>
              <serviceschema>
                   <propertyreference ref="i2" required="yes" />
              </serviceschema>
         </service>
         </results>
    </cnrp>
 
 
 
 6.2 Sending A Query and Getting A Response
 
    This is the query that is sent from the client to the server:
 
 
    <?xml version="1.0"?>
    <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN"
     "http://ietf.org/dtd/cnrp-1.0.dtd">
    <cnrp>
     <query>
        <commonname>Fido</commonname>
        <property name="geography" type="iso3166-2">
           CA-QC</property>
        <property name="geography" type="iso3166-1">CA</property>
        <property name="language" type="rfc1766">fr-CA</property>
     </query>
    </cnrp>
 
 
    This is the result set.  It is sent back in response to the query.
    This result set includes a referral and a non-fatal error.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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    <?xml version="1.0"?>
    <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN"
     "http://ietf.org/dtd/cnrp-1.0.dtd">
    <cnrp>
         <results>
              <service id="i0">
                   <serviceuri>http://acmecorp.com</serviceuri>
              </service>
              <service id="i1">
                   <serviceuri>http://serverfarm.acmecorp.com</serviceuri>
              </service>
              <service id="i2">
                    <serviceuri>http://servers.acmecorp.co.uk</serviceuri>
              </service>
              <resourcedescriptor>
                        <commonname>Fidonet</commonname>
                        <id>1333459455</id>
                        <resourceuri>http://www.fidonet.ca</resourceuri>
                        <serviceref ref="i0" />
                        <description>This is ye olde Canadian
                           Fidonet</description>
              </resourcedescriptor>
              <resourcedescriptor>
                        <commonname>Fidonet</commonname>
                        <id>1333459455</id>
                        <resourceuri>http://host:port/bla</resourceuri>
                        <serviceref ref="i1" />
                        <description>An old Fidonet node</description>
              </resourcedescriptor>
              <referral><serviceref ref="i2" /></referral>
              <status code="3.1.1">The language property 'fr-CA' was ignored</status>
         </results>
    </cnrp>
 
 
 
 7. Transport
 
    Two CNRP transport protocols are specified.  HTTP is used due to its
    popularity and ease of integration with other web applications.  SMTP
    is also used as a way to illustrate a protocol that has a much
    different range of  latency than most protocols.
 
 7.1 HTTP Transport
 
    The HTTP transport is fairly simple.  The client connects to an HTTP
    based CNRP server and issues a request using the POST method to the
    "/" path with the Content-type and Accept header set to
 
 
 
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    "application/xml".  The content of the POST body is the CNRP XML
    document that is being sent.  All HTTP 1.1 features are allowed
    during the request.
 
    The results are sent back to the client with a Content-Type of
    "application/xml".  The body of the result is the CNRP XML document
    being  sent to the client.
 
 7.2 SMTP Transport
 
    The SMTP transport is very similar to the HTTP transport.  Since
    there is no method to specify, the CNRP XML document is simply sent
    to a particular SMTP endpoint with its Content-Type set to
    "application/xml".  The server responds by sending a response to the
    originator of the request with the results in the body and the
    Content-Type set to "application/xml".  The Service MUST specify at
    least one SMTP target (email address) to contact.
 
 8. Security Considerations
 
    Three security threats exist for CNRP or applications that depend on
    it: Man in the Middle attacks, malicious agents posing as a service
    by spoofing a Service object, and denial of service attacks caused by
    adding  a new level of indirection for resolution of a resource.
 
    The proposed solution for man in the middle attacks is to utilize
    transport level authentication and encryption where available.  In
    the case where the transport can't provide the level of required
    authentication, individual entries or the entire response can be
    signed/encrypted using XML signature methods being developed by the
    XMLDSIG Working Group.
 
    In the case of where a service attempts to pose as another by
    spoofing the serviceuri in the Service object, the Service object
    should be signed.  A client can then verify the Service object's
    veracity by verifying the signature.  How the client obtains that
    authoritative public key is out of scope since it depends on the
    service discovery problem.
 
    While this document cannot propose a solution for Denial Of Service
    (DOS) attacks it can illustrate that, like many other cases, any time
    a new level of indirection is created an opportunity for a DOS attack
    is created.  Service providers are encouraged to be aware of this and
    to act accordingly to mitigate the effects of a DOS attack.
 
 9. IANA Considerations
 
    The major consideration for the IANA is that the IANA will be
 
 
 
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    registering well known properties, property types and status
    messages.  It will not register values.  Since this document does not
    discuss CNRP service discovery, the IANA will not be registering the
    existence of servers or Server objects.
 
    There are three types of entities the IANA can register: properties,
    property types, and status messages.  If a property or type is not
    registered with the IANA then they must start with "x-".  Status
    messages can be created for local consumption and not registered.
    There is no requirement that new status messages are mandatory to
    implement unless this document is updated.  Status message
    registrations are more for informational purposes.
 
    The required information for the registration of a new property is
    the property's name, its default type, and a general description.  A
    new type requires the type's name, what properties it is valid for,
    and a description.  A new status message requires the X.Y.ZZZ code
    and a brief description of the state being communicated.
 
    All properties, types and status messages are registered on a First
    Come First Served basis with no review by the IANA or any group of
    experts.  The concensus opinion of the CNRP Working Group is that
    review of property registrations should occur once there is
    operational experience with the protocol and an actual need for the
    review.  If, at some future date, this policy needs to change this
    document will be updated.
 
    The property and type registration templates found in Appendix A
    should be registered by the IANA at publication time of this
    document.
 
 References
 
    [1]   United States, "North American Industry Classification System",
          January 1997, <http://www.census.gov/epcd/www/naics.html>.
 
    [2]   Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
          Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
          HTTP/1.1", RFC 2616, June 1999.
 
    [3]   Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
          Resource Identifiers (URI): Generic Syntax", RFC 2396, August
          1998.
 
    [4]   Alvestrand, H., "Tags for the Identification of Languages", RFC
          1766, March 1995.
 
    [5]   Moats, R., "URN Syntax", RFC 2141, May 1997.
 
 
 
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    [6]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
          Levels", RFC 2119, BCP 14, March 1997.
 
    [7]   Bray, T., Paoli, J. and C. Sperberg-McQueen, "Extensible Markup
          Language (XML) 1.0", February 1998.
 
    [8]   Mealling, M., "A URI Scheme for the Common Name Resolution
          Protocol", RFC XXXX, draft-ietf-cnrp-uri-01.txt (work in
          progress), December 1999.
 
    [9]   Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893,
          January 1996.
 
    [10]  "Country and Region Codes", ISO 3166, January 1996.
 
 
 Authors' Addresses
 
    Nico Popp
    RealNames Corporation
    2 Circle Star Way, 2nd Floor
    San Carlos, CA  94070-1350
    US
 
    Phone: (650) 298 8080
    EMail: nico@realnames.com
 
 
    Michael Mealling
    VeriSign, Inc.
    21345 Ridgetop Circle
    Sterling, VA  20166
    US
 
    EMail: michael@verisignlabs.com
 
 
    Marshall Moseley
    Netword, Inc.
    702 Russell Avenue
    Gaithersburg, MD  20877-2606
    US
 
    Phone: (240) 631-1100
    EMail: marshall@netword.com
 
 
 
 
 
 
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 Appendix A. Appendix A: Well Known Property and Type Registration
             Templates
 
 A.1 Properties
 
    Property Name: geography
    Default Type: iso3166-1
    Description: A geographic location
 
    Property Name: language
    Default Type: rfc1766
    Description: A language specification
 
    Property Name: category
    Default Type: freeform
    Description: A node in some system of semantic relationships that is
    considered relevant to the common-name.
 
    Property Name: range
    Default Type: range
    Description: A range given in the format "x,y" where x is the
    starting point and y is the length.  This property is used by the
    client to tell the server that is is requesting a subrange of the
    results.
 
    Property Name: dataseturi
    Default Type: uri
    Description: A URI used to disambiguate between two Datasets offered
    by the same Service.
 
 A.2 Types
 
    Type: freeform
    Property: category
    Description: The value is to be interpreted by the server the best
    way it knows how.  This value has no defined structure.
 
    Type: freeform
    Property: geography
    Description: The value is to be interpreted by the server the best
    way it knows how.  This value has no defined structure.
 
    Type: freeform
    Property: language
    Description: The value is to be interpreted by the server the best
    way it knows how.  This value has no defined structure.
 
    Type: iso3166-2
 
 
 
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    Property: geography
    Description: The combination of country and sub-region codes found in
    ISO 3166-2 [10].
 
    Type: iso3166-1
    Property: Geography
    Description: Country Codes found in ISO 3166-1 [10].
 
    Type: postalcode
    Property: Geography
    Description: A postal code that is valid for some region.  A good
    example is the Zip code system used in the US.
 
    Type: lat-long
    Property: Geography
    Description:
 
       Values for latitude and longitude shall be expressed as decimal
       fractions of degrees.  Whole degrees of latitude shall be
       represented by a two-digit decimal number ranging from 0 through
       90.  Whole degrees of longitude shall be represented by a decimal
       number ranging from 0 through 180.  When a decimal fraction of a
       degree is specified, it shall be separated from the whole number
       of degrees by a decimal point.  Decimal fractions of a degree may
       be expressed to the precision desired.
 
       Latitudes north of the equator shall be specified by a plus sign
       (+), or by the absence of a minus sign (-), preceding the
       designating degrees.  Latitudes south of the Equator shall be
       designated by a minus sign (-) preceding the two digits
       designating degrees.  A point on the Equator shall be assigned to
       the Northern Hemisphere.
 
       Longitudes east of the prime meridian shall be specified by a plus
       sign (+), or by the Longitudes west of the meridian shall be
       designated by minus sign (-) preceding the digits designating
       degrees.  A point on the prime meridian shall be assigned to the
       Eastern Hemisphere.  A point on the 180th meridian shall be
       assigned to the Western Hemisphere.  One exception to this last
       convention is permitted.  For the special condition of describing
       a band of latitude around the earth, the East Bounding Coordinate
       data element shall be assigned the value +180 (180) degrees.
 
       Any spatial address with a latitude of +90 (90) or -90 degrees
       will specify the position at the North or South Pole,
       respectively.  The component for longitude may have any legal
       value.
 
 
 
 
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       With the exception of the special condition described above, this
       form is specified in Department of Commerce, 1986, Representation
       of geographic point locations for information interchange (Federal
       Information Processing Standard 70-1):  Washington,  Department of
       Commerce, National Institute of Standards and Technology.
 
             DEGREES   = *PLUSMINUS DIGITS '.' DIGITS
             PLUSMINUS = + | -
             DIGITS    = DIGIT *DIGIT
             DIGIT     = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 
 
    Type: rfc1766
    Property: Language
    Description: language codes as defined by RFC 1766 [4]
 
    Type: naics
    Property: Category
    Description: North American Industry Code System [1]
 
    Type: uri
    Property: dataseturi
    Description: A URI adhering to the 'absoluteURI' production of the
    Collected ABNF found in [3]
 
 Appendix B. Status Codes
 
 B.1 Level 1 (Informative) Codes
 
    1.0.0 -- Undefined Information
       This code is used for any non-categorizable and informative
       message.  If, for example, the server wanted to tell the client
       that the systems administrator's cat has blue hair, then this code
       would be the appropriate place for this information.
 
    1.1.0 -- Query related information
       This code is used for any informative information concerning the
       query that client sent.  For example, "The query you sent was
       rather interesting!".
 
    1.2.0 -- An informative message pertaining to the Service
       This message concerns the Service in the general sense.
 
 
 B.2 Level 2 (Success) Codes
 
    2.0.0 -- Something undefined succeeded
       There was success but the situation that this message concerns is
 
 
 
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       undefined.
 
    2.1.0 -- Query succeeded
       The query succeeded.  This message MUST be returned when there
       were no results that matched the query.  I.e.  the query was
       successfully handled and the correct set of results contained no
       resources or referrals.  The lack of results is not an error but a
       successful statement about the common-name.
 
    NOTE: The apparent lack of 2.X.X level codes is caused by success
    usually being indicated not by a status message but by the server
    returning only the objects that the client requested.
 
 B.3 Level 3 (Partial Success) Codes
 
    3.0.0 -- Something undefined was only partially successful
       Some request by the client was only partially successful.  The
       exact situation or cause of that partial failure is not defined.
 
    3.1.0 -- The query was only partially successful
 
    3.1.1 -- The query contained invalid or unsupported properties
       The query contained invalid or unsupported property names, types
       or values.  The invalid properties were ignored and the query
       processed.
 
    3.1.2 -- The XML was well formed but invalid
       The XML sent by the client was well formed but invalid.  The
       server was smart enough to figure out what the client was talking
       about and return some results.
 
    3.1.3 Server does not support datasets
       This status should be generated by servers that do not handle
       datasets.  A server can send this status message at any time but
       it especially useful for when a server recieves a query from a
       client that contains a dataseturi.  In this case and if the client
       is doing rigorous loop detection, the client should consider this
       entire service to have been visited.
 
    3.1.4 The first dataset in the list of datasets you gave in the
    query was the only one used.
       This status message is used by a server to indicate the situation
       where a client has included several dataseturis in its query and
       the server can only support one at a time.  In this case the
       server is explicitly stating that it used the first dataseturi
       only.  The client should consider that only the first dataseturi
       specified was processed correctly.  The client should consider
       that the remaining datasets in the query were ignored completely.
 
 
 
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       They would need to be sent individually as referrals if the client
       really cares about those results.  Only the first
       serviceuri/dataseturi pair should be marked as visited if loop
       detection is being handled.
 
    3.1.5 This dataset not supported.
       This message is used to indicate that a specific dataseturi sent
       in a query by a client is not supported by the server.This
       serviceuri/dataseturi pair should be considered as visited by the
       client.  If this message is sent in reply to a query specifying
       multiple datasets, the client should behave the same as if it
       recieved the 3.1.3 message from above.  It should be considered
       bad form for a server to send this status message back in response
       to a query with multiple datasets because it is ambigious.
 
    3.2.0 -- The server caused a partially successful event
       Due to some internal server error, the results returned were
       incomplete.
 
    3.2.1 -- Some referral server was unavailable
       This status message is used to denote that one or more of the
       referral services that are normally queried was unavailable.
       Results were generated but they may not be representative of a
       complete answer.
 
 
 B.4 Level 4 (Transient Failure) Codes
 
    4.0.0 -- Something undefined caused a persistent transient failure
 
    4.1.0 -- There was an error in the query that made it unable to be
    interpreted
 
    4.2.0 -- The query was to complex
       The query as specified was too complex for this Service to handle.
 
    4.2.1 -- The Service was too busy
       Due to resource constraints, the entire service is too busy to
       handle requests.  This means that any of the Servers cooperating
       in providing this Service would have also returned this same
       message.
 
    4.2.2 -- The Server is in maintenance
       This server is now in maintenance mode.  Try another server from
       this service or try again at a later time.
 
    4.2.3 -- The Server had an internal error
       There was an internal error that caused the server to fail
 
 
 
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       completly.
 
 
 B.5 Level 5 (Permanent Failures) Codes
 
    5.0.0 -- Something undefined caused a permanent failure
 
    5.1.0 -- The query permanently failed
 
    5.2.0 -- The service had a permanent failure
 
    5.2.1 -- This Service is no longer available.
       This Service has decided to no longer make itself available.
 
    5.2.2 -- The Server had a permanent failure
       This server has permanently failed.  Try another server from this
       service.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 Full Copyright Statement
 
    Copyright (C) The Internet Society (2002).  All Rights Reserved.
 
    This document and translations of it may be copied and furnished to
    others, and derivative works that comment on or otherwise explain it
    or assist in its implementation may be prepared, copied, published
    and distributed, in whole or in part, without restriction of any
    kind, provided that the above copyright notice and this paragraph are
    included on all such copies and derivative works.  However, this
    document itself may not be modified in any way, such as by removing
    the copyright notice or references to the Internet Society or other
    Internet organizations, except as needed for the purpose of
    developing Internet standards in which case the procedures for
    copyrights defined in the Internet Standards process must be
    followed, or as required to translate it into languages other than
    English.
 
    The limited permissions granted above are perpetual and will not be
    revoked by the Internet Society or its successors or assigns.
 
    This document and the information contained herein is provided on an
    "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
    TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
    BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
    HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
    MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 
 Acknowledgement
 
    Funding for the RFC Editor function is currently provided by the
    Internet Society.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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