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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: March 14, 2001                                      M. Mealling
                                                 Network Solutions, Inc.
                                                              M. Moseley
                                                           Netword, Inc.
                                                      September 13, 2000


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
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     The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on March 14, 2001.

Copyright Notice

   Copyright (C) The Internet Society (2000). All Rights Reserved.


   Please send comments on this draft to CNRP-IETF@LISTS.INTERNIC.NET.

   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
   associated with a resource.

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   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 intended to address the issues of internationalization and
   privacy as well. 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 . . . . . . . . . . . . . . . . . . . .  6
   3.5     Queries  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.6     Hints  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.      Object Model . . . . . . . . . . . . . . . . . . . . . . .  8
   4.1     Properties . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.1.1   Core properties  . . . . . . . . . . . . . . . . . . . . .  8
   4.1.2   Abstract and custom properties . . . . . . . . . . . . . .  9
   4.1.3   Base properties  . . . . . . . . . . . . . . . . . . . . .  9
   4.1.4   Common name string encoding and equivalence rules  . . . . 10
   4.2     Objects  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   4.2.1   Query  . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Logical operations within a Query  . . . . . . . . . . . . 11
   4.2.2   Results  . . . . . . . . . . . . . . . . . . . . . . . . . 12 ResourceDescriptor . . . . . . . . . . . . . . . . . . . . 13
   4.2.3   Service  . . . . . . . . . . . . . . . . . . . . . . . . . 13 Datasets . . . . . . . . . . . . . . . . . . . . . . . . . 14 Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 15
   4.2.4   Status Messages  . . . . . . . . . . . . . . . . . . . . . 17 Status of CNRP, Not the Transport  . . . . . . . . . . . . 18 Codes and Description  . . . . . . . . . . . . . . . . . . 18 Status Codes . . . . . . . . . . . . . . . . . . . . . . . 18
   4.2.5   Referral . . . . . . . . . . . . . . . . . . . . . . . . . 19
   4.2.6   Discoverability: ServiceQuery and Schema . . . . . . . . . 20
   5.      XML DTD for CNRP . . . . . . . . . . . . . . . . . . . . . 22
   6.      Examples . . . . . . . . . . . . . . . . . . . . . . . . . 24
   6.1     Service Description Request  . . . . . . . . . . . . . . . 24
   6.2     Sending A Query and Getting A Response . . . . . . . . . . 26

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   6.3     No Result  . . . . . . . . . . . . . . . . . . . . . . . . 27
   6.4     Error Conditions . . . . . . . . . . . . . . . . . . . . . 27
   7.      Transport  . . . . . . . . . . . . . . . . . . . . . . . . 27
   7.1     HTTP Transport . . . . . . . . . . . . . . . . . . . . . . 27
   7.2     SMTP Transport . . . . . . . . . . . . . . . . . . . . . . 28
   8.      Security Considerations  . . . . . . . . . . . . . . . . . 28
   9.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 28
           References . . . . . . . . . . . . . . . . . . . . . . . . 29
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 30
   A.      Appendix A: Well Known Property and Type Registration
           Templates  . . . . . . . . . . . . . . . . . . . . . . . . 30
   A.1     Properties . . . . . . . . . . . . . . . . . . . . . . . . 30
   A.2     Types  . . . . . . . . . . . . . . . . . . . . . . . . . . 31
   B.      Status Codes . . . . . . . . . . . . . . . . . . . . . . . 32
   B.1     Level 1 (Informative) Codes  . . . . . . . . . . . . . . . 32
   B.2     Level 2 (Success) Codes  . . . . . . . . . . . . . . . . . 32
   B.3     Level 3 (Partial Success) Codes  . . . . . . . . . . . . . 33
   B.4     Level 4 (Transient Failure) Codes  . . . . . . . . . . . . 33
   B.5     Level 5 (Permanent Failures) Codes . . . . . . . . . . . . 33
           Full Copyright Statement . . . . . . . . . . . . . . . . . 35

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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. Although the protocol's primary function is resolution,
   it is intended to address the issues of internationalization and
   privacy as well. 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,

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   etc).  A single common name may be associated with different data
   records, 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 herein.)

   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
      "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
   "servers". If the data contained in all its servers is identical

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   (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 MUST 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 MUST 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 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.

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

   Since CNRP is completely encapsulated within its XML definition it
   can be considered transport-independent.  However, because there
   must be a standardized way for a client to contact and negotiate
   with a server, CNRP requires support for HTTP 1.1  (RFC 2616)[2] or
   greater on the default CNRP port of 1096.

   A particular service may choose to change to a different transport
   (via statements within the XML DTD), but minimally, all initial
   contacts between a client and a server that the client knows nothing
   about can be assumed to function over HTTP. 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

   The guarantee interoperability, the following provisions apply:

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   o  XML queries and responses MUST be encoded as UTF-8.

      Note: As in any XML document, numeric character references may be
   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
   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 now anything about the Service,
       the client MAY assume that it can at least issue the request via
   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
   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

   An example of this would be the required property "language", in
   which a query might be created that specifies the primary language
   in which you want to see results, the secondary language, and so on.
   So seeing results in US English followed by European French and

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   South American Spanish would be:

      <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

4. Object Model

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.

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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

   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
   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

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   o  Geography:
      The geographical region or location associated with a resource.
      Some of the possible types for:
      *  '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").
      *  'latitude-longitude-elevation': the latitude, longitude and
         elevation of a geographical location expressed in a comma
         delimited string (i.e. "latitude,longitude,elevation")
      *  'GPS': a geographical location expressed using the standard
         GPS coordinates system
   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.
      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
   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

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   treated as CNRP services. Consequently, string equivalence rules are
   not part of the CNRP protocol specification. For example, the query

   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

   It is also important to note that XML treats whitespace as a special
   case in many situations. In some cases it collapses whitespace into
   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 a common name, or an 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:

           <property name="range" type="start-length">1-5</property>
   </query> 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:

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        <property name="language" type="rfc1766">

   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:
      property = value1 OR property = value2 OR property = valueN

   Will be expressed as:


   So if there are different properties expressed, CNRP ANDs them; if
   there are multiples of the same property expressed, CNRP ORs them.

   It is important to underline that this form is only applicable to
   properties. 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.

        <property name="language" type="rfc1766">de-DE</property>
        <property name="language" type="rfc1766">fr-FR</property>
        <property name="language" type="rfc1766">*</property>

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

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   relevance ranking is specific to a given service). In that case,
   however, note that results originating from the same service remain
   ordered. 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 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.

        <service id="0">
        <resourcedescriptor id="1">
             <property name="language" type="rfc1766">de-DE</property>
             <serviceref ref="0" />

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. A Service object can include a a brief textual
   description of the service.

        <description>foo.com is a CNRP service specialized on cocktail

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   The service object can 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:

        <property name="category" type="freeform">companies</property>
        <property name="geography" type="ISO3166-1">FR</property>
   </service> 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 mapings 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. This example illustrates how the service object
   would look as it defines two datasets:

   <service id="0">
       <dataset id="1">
           <property name="dataseturi">urn:oid:</property>
           <property name="language">en-us</property>
           <property name="language">en-gb</property>
           <description>This is an example of a complex CNRP service
       <dataset id="2">
           <property name="dataseturi">urn:oid:</property>
           <property name="language">fr</property>

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   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

      <commonname>toys r us</commonname>
      <property name="dataseturi">urn:oid:</property>

   It is important to note that resolution rules (i.e. string
   equivalence, relevance raking, 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.

      <serviceref ref="0" /><datasetref ref="1" />

   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. 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 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

   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

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   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.

           <property name="geography" type="ISO3166-1">US</property>
           <property name="geography" type="ISO3166-1">FR</property>

   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.
   For example, imagine a CNRP service that acts as a proxy for
   multiple CNRP services. (it is actually a requirement that CNRP
   allows the aggregation of results from different sources). In this
   mode, the proxy service contacts each CNRP sub-services 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">

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             <service id="0">
                  <dataset id="1">
                     <property name="dataseturi">
                  <dataset ref="2">
                     <property name="dataseturi">
             <service id="3">
             <service id="4">
                 <dataset id="4">
                     <property name="dataseturi">
                       <serviceref ref="0" /><datasetref ref="1" />
                       <description>This is ye olde Canadian
                       <serviceref ref="1" />
                 <serviceref id="0" /><datasetref ref="2" />

4.2.4 Status Messages

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   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. 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 2 and a status message
   refers to that block then it can put that ID in its ref attribute.

            <status code="x.y.z" ref="2">
                 The CNRP foo.com database is temporarily unreachable
       </results> 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

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         themselves denote success. In other cases results were
         returned but some information needs to be returned to the

   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

      *  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

   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 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.

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        <service id="0">
             <property name="dataseturi">
             <property name="dataseturi">
             <property name="language" type="iso646">de-DE</property>
             <serviceref ref="0" />
             <property name="dataseturi">

   Like other CNRP objects, a referral can be further described using
   custom properties. Specifically, the well known Base Property of
   'dataseturi' is used by a referral to disambiguate between two
   Datasets offered by one Service. Also, a referral can have an ID
   attribute that is used by a status message to talk about a
   particular referral block.

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

   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
   3.  The properties that belong to the query interface (Query schema)

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   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
      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
   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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           <propertydeclaration id="1">
           <propertydeclaration id="2">
             <propertyreference required="yes idref="1"/>
             <propertyreference required="yes" idref="1"/>
             <propertyreference required="yes" idref="2"/>

   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.


   <!-- 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)>
   <!-- The name of the property -->
   <!ATTLIST property name CDATA #REQUIRED>

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   <!-- The type of the property -->
   <!ATTLIST property type CDATA "freeform">

        Services, Resourcedescriptors, Referrals and Errors can occur in
        any order and repeat any number of times.
   <!ELEMENT results (status? |
                      ( service+,
                        ( status*,

   <!ELEMENT resourcedescriptor (commonname,id,resourceuri,
       serviceref, datasetref?,
   <!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*,
   <!-- The time to live of the schema in seconds since it was retrieved -->
   <!ATTLIST service ttl CDATA "0">

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   <!ATTLIST service id ID #IMPLIED>
   <!ELEMENT serviceuri (#PCDATA)>
   <!ELEMENT servers (server+)>
   <!ELEMENT server (serveruri, property*)>
   <!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

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   <?xml version="1.0"?>
   <!DOCTYPE cnrp PUBLIC "-//IETF//DTD CNRP 1.0//EN">
        <servicequery />

   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">
        <service ttl="43200">
             <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">
                  <propertydeclaration id="1">
                       <propertytype default="yes">freeform</propertytype>
                       <propertytype default="no">domainname</propertytype>
                       <propertydeclaration id="2">
                       <propertytype default="yes">URI</propertytype>
                  <propertyreference ref="1" required="yes" />
                  <propertyreference ref="1" required="yes" />

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                  <propertyreference ref="2" required="yes" />

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">
       <property name="geography" type="iso3166-2">
       <property name="geography" type="iso3166-1">CA</property>
       <property name="language" type="rfc1766">fr-CA</property>

   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">
             <service id="0">
             <service id="1">
             <service id="2">
                       <serviceref ref="0" />
                       <description>This is ye olde Canadian
                       <serviceRef ref="1" />
             <referral><serviceRef ref="2" /></referral>
             <status code="3.1.1">The language property 'fr-CA' was ignored</status>

6.3 No Result

6.4 Error Conditions

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".

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

   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
   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

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   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. If, at some future date, this policy needs to change this
   document will be updated.

   See Appendix A some example property and type registrations.


   [1]  United States, "North American Industry Classification System",
        January 1997.

   [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.T. and L. Masinter, "Uniform
        Resource Identifiers (URI): Generic Syntax", RFC 2396, August

   [4]  Alvestrand, H., "Tags for the Identification of Languages", RFC
        1766, March 1995.

   [5]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [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. M. Sperberg-McQueen, "Extensible
        Markup Language (XML) 1.0", February 1998.

   [8]  Mealling, M., "A URI Scheme for the Common Name Resolution
        Protocol", December 1999.

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   [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

   Phone: (650) 298 8080
   EMail: nico@realnames.com

   Michael Mealling
   Network Solutions, Inc.
   505 Huntmar Park Drive
   Herndon, VA  22070

   Phone: (703) 742-0400
   EMail: michaelm@netsol.com

   Marshall Moseley
   Netword, Inc.
   702 Russell Avenue
   Gaithersburg, MD  20877-2606

   Phone: (240) 631-1100
   EMail: marshall@netword.com

Appendix A. Appendix A: Well Known Property and Type Registration

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

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   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

   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
   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: gps
   Property: Geography
   Description: A code in the format used by the Global Positioning

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   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
   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.

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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
   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.
   3.2.0 -- The server caused a partially successful event
      Due to some internal server error, the results returned were
   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
   4.2.0 -- The query was to complex
      The query as specified was too complex for this Service to
   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
   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

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.

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      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

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