Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/Registro.it
Expires: June 22, August 14, 2020                                   S. Hollenbeck
                                                           Verisign Labs
                                                       December 20, 2019
                                                       February 11, 2020

  Registration Data Access Protocol (RDAP) Query Parameters for Result
                           Sorting and Paging
              draft-ietf-regext-rdap-sorting-and-paging-07
              draft-ietf-regext-rdap-sorting-and-paging-08

Abstract

   The Registration Data Access Protocol (RDAP) does not include core
   functionality for clients to provide sorting and paging parameters
   for control of large result sets.  This omission can lead to
   unpredictable server processing of queries and client processing of
   responses.  This unpredictability can be greatly reduced if clients
   can provide servers with their preferences for managing large
   responses.  This document describes RDAP query extensions that allow
   clients to specify their preferences for sorting and paging result
   sets.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on June 22, August 14, 2020.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
   2.  RDAP Query Parameter Specification  . . . . . . . . . . . . .   4
     2.1.  Sorting and Paging Metadata . . . . . . . . . . . . . . .   4
     2.2.  "count" Parameter . . . . . . . . . . . . . . . . . . . .   6
     2.3.  "sort" Parameter  . . . . . . . . . . . . . . . . . . . .   7
       2.3.1.  Sorting Properties Declaration  . . . . . . . . . . .   7
       2.3.2.  Representing Sorting Links  . . . . . . . . . . . . .  11
     2.4.  "cursor" Parameter  . . . . . . . . . . . . . . . . . . .  13
       2.4.1.  Representing Paging Links . . . . . . . . . . . . . .  15  13
       2.4.2.  Paging Responses to POST Requests . . . . . . . . . .  16  14
   3.  Negative Answers  . . . . . . . . . . . . . . . . . . . . . .  18  16
   4.  RDAP Conformance  . . . . . . . . . . . . . . . . . . . . . .  19  17
   5.  Implementation Considerations . . . . . . . . . . . . . . . .  19  17
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  19  17
     6.1.  IIT-CNR/Registro.it . . . . . . . . . . . . . . . . . . .  19  17
     6.2.  Google Registry . . . . . . . . . . . . . . . . . . . . .  20  18
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20  18
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  20  18
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21  19
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  21  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  23  21
   Appendix A.  Approaches to Result Pagination  . . . . . . . . . .  22
     A.1.  Specific Issues Raised by RDAP  . . . . . . . . . . . . .  23
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24  25

1.  Introduction

   The availability of functionality for result sorting and paging
   provides benefits to both clients and servers in the implementation
   of RESTful services [REST].  These benefits include:

   o  reducing the server response bandwidth requirements;
   o  improving server response time;
   o  improving query precision and, consequently, obtaining more
      reliable results;

   o  decreasing server query processing load;
   o  reducing client response processing time.

   Approaches to implementing features for result sorting and paging can
   be grouped into two main categories:

   1.  Sorting and paging are implemented through the introduction of
       additional parameters in the query string (i.e.  ODATA protocol
       [OData-Part1]);

   2.  Information related to the number of results and the specific
       portion of the result set to be returned, in addition to a set of
       ready-made links for the result set scrolling, are inserted in
       the HTTP header of the request/response.

   However, there are some drawbacks associated with the use of the HTTP
   header.  First, the header properties cannot be set directly from a
   web browser.  Moreover, in an HTTP session, the information on the
   status (i.e. the session identifier) is usually inserted in the
   header or in the cookies, while the information on the resource
   identification or the search type is included in the query string.
   The second approach is therefore not compliant with the HTTP standard
   [RFC7230].  As a result, this document describes a specification
   based on the use of query parameters.

   Currently, the RDAP protocol [RFC7482] defines two query types:

   o  lookup: the server returns only one object;
   o  search: the server returns a collection of objects.

   While the lookup query does not raise issues in the response
   management, the search query can potentially generate a large result
   set that could be truncated according to the server limits.  In
   addition, it is not possible to obtain the total number of the
   objects found that might be returned in a search query response
   [RFC7483].  Lastly, there is no way to specify sort criteria to
   return the most relevant objects at the beginning of the result set.
   Therefore, the client might traverse the whole result set to find the
   relevant objects or, due to truncation, could not find them at all.

   The specification described in this document extends RDAP query
   capabilities to enable result sorting and paging, by adding new query
   parameters that can be applied to RDAP search path segments.  The
   service is implemented using the Hypertext Transfer Protocol (HTTP)
   [RFC7230] and the conventions described in RFC 7480 [RFC7480].

   The implementation of the new parameters is technically feasible, as
   operators for counting, sorting and paging rows are currently
   supported by the major RDBMSs.

1.1.  Conventions Used in This Document

   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 [RFC2119].

2.  RDAP Query Parameter Specification

   The new query parameters are OPTIONAL extensions of path segments
   defined in RFC 7482 [RFC7482].  They are as follows:

   o  "count": a boolean value that allows a client to request the total
      number of objects found (that due to truncation can be different
      from the number of returned objects);

   o  "sort": a string value that allows a client to request a specific
      sort order for the result set;

   o  "cursor": a string value representing a pointer to a specific
      fixed size portion of the result set.

   Augmented Backus-Naur Form (ABNF) [RFC5234] is used in the following
   sections to describe the formal syntax of these new parameters.

2.1.  Sorting and Paging Metadata

   According to most advanced principles in REST design, collectively
   known as HATEOAS (Hypermedia as the Engine of Application State)
   ([HATEOAS]), a client entering a REST application through an initial
   URI should use the server-provided links to dynamically discover
   available actions and access the resources it needs.  In this way,
   the client is not requested to have prior knowledge of the service
   and, consequently, to hard code the URIs of different resources.
   This would allow the server to make URI changes as the API evolves
   without breaking the clients.  Definitively, a REST service should be
   as self-descriptive as possible.

   Therefore, servers implementing the query parameters described in
   this specification SHOULD provide additional information in their
   responses about both the available sorting criteria and the possible
   pagination.  Such information is collected in two OPTIONAL response
   elements named, respectively, "sorting_metadata" and
   "paging_metadata".

   The "sorting_metadata" element contains the following properties:

   o  "currentSort": "String" (OPTIONAL) either the value of sort
      "parameter" as specified in the query string or the sort applied
      by default, if any;

   o  "availableSorts": "AvailableSort[]" (OPTIONAL) an array of objects
      each one describing an alternate available sorting criterion.
      Members are:

      *  "property": "String" (REQUIRED) the name that can be used by
         the client to request the sorting criterion;
      *  "default": "Boolean" (REQUIRED) whether the sorting criterion
         is applied by default;
      *  "jsonPath": "String" (OPTIONAL) the JSON Path of the RDAP field
         corresponding to the property;
      *  "links": "Link[]" (OPTIONAL) an array of links as described in
         RFC 8288 [RFC8288] containing the query string that applies the
         sorting criterion.

   At least one between "currentSort" and "availableSorts" MUST be
   present.

   The "paging_metadata" element contains the following fields:

   o  "totalCount": "Numeric" (OPTIONAL) a numeric value representing
      the total number of objects found.  It is MUST be provided if the
      query string contains the "count" parameter;

   o  "pageSize": "Numeric" (OPTIONAL) a numeric value representing the
      number of objects returned in the current page.  It is MUST be
      provided when the total number of objects exceeds the page size.
      This property is redundant for clients because the page size can
      be derived from the length of the search results array but it can
      be helpful if the end user interacts with the server through a web
      browser;

   o  "pageNumber": "Numeric" (OPTIONAL) a numeric value representing
      the number of the current page in the result set.It is MUST be
      provided when the total number of objects found exceeds the page
      size;

   o  "links": "Link[]" (OPTIONAL) an array of links as described in RFC
      8288 [RFC8288] containing the reference to the next page.  In this
      specification, only the forward pagination is dealt because it is
      considered satisfactory in order to traverse the result set.
      Examples of additional references are to: the previous page, the
      first page, the last page.

   At least one between "totalCount" and "links" MUST be present.

2.2.  "count" Parameter

   Currently, the RDAP protocol does not allow a client to determine the
   total number of the results in a query response when the result set
   is truncated.  This is rather inefficient because the user cannot
   evaluate the query precision and, at the same time, cannot receive
   information that could be relevant.

   The "count" parameter provides additional functionality (Figure 1)
   that allows a client to request information from the server that
   specifies the total number of elements matching the search pattern.

   https://example.com/rdap/domains?name=*nr.com&count=true

      Figure 1: Example of RDAP query reporting the "count" parameter

   The ABNF syntax is the following:

      count = "count=" ( trueValue / falseValue )
      trueValue = ("true" / "yes" / "1")
      falseValue = ("false" / "no" / "0")

   A trueValue means that the server MUST provide the total number of
   the objects in the "totalCount" field of the "paging_metadata"
   element (Figure 2).  A falseValue means that the server MUST NOT
   provide this number.

   {
     "rdapConformance": [
           "rdap_level_0",
           "paging_level_0"
     ],
     ...
     "paging_metadata": {
       "totalCount": 43
     },
     "domainSearchResults": [
       ...
     ]
   }

     Figure 2: Example of RDAP response with "paging_metadata" element
                     containing the "totalCount" field

2.3.  "sort" Parameter

   The RDAP protocol does not provide any capability to specify results
   sort criteria.  A server could implement a default sorting scheme
   according to the object class, but this feature is not mandatory and
   might not meet user requirements.  Sorting can be addressed by the
   client, but this solution is rather inefficient.  Sorting features
   provided by the RDAP server could help avoid truncation of relevant
   results.

   The "sort" parameter allows the client to ask the server to sort the
   results according to the values of one or more properties and
   according to the sort direction of each property.  The ABNF syntax is
   the following:

      sort = "sort=" sortItem *( "," sortItem )
      sortItem = property-ref [":" ( "a" / "d" ) ]
      property-ref = ALPHA *( ALPHA / DIGIT / "_" )

   "a" means that the ascending sort MUST be applied, "d" means that the
   descending sort MUST be applied.  If the sort direction is absent, an
   ascending sort MUST be applied (Figure 3).

   https://example.com/rdap/domains?name=*nr.com&sort=name

   https://example.com/rdap/domains?name=*nr.com&sort=registrationDate:d

   https://example.com/rdap/domains?name=*nr.com&sort=lockedDate,name

      Figure 3: Examples of RDAP query reporting the "sort" parameter

   With the only exception of the sort on IP addresses, servers MUST
   implement sorting according to the JSON value type of the RDAP field
   the sorting property refers to: JSON strings MUST be sorted
   lexicographically and JSON numbers MUST be sorted numerically.  Even
   if IP addresses are represented as JSON strings, they MUST be sorted
   based on their numeric conversion.

   If the "sort" parameter reports an allowed sorting property, it MUST
   be provided in the "currentSort" field of the "sorting_metadata"
   element.

2.3.1.  Sorting Properties Declaration

   In the "sort" parameter ABNF syntax, property-ref represents a
   reference to a property of an RDAP object.  Such a reference could be
   expressed by using a JSON Path.  The JSON Path in a JSON document

   [RFC8259] is equivalent to the XPath [W3C.CR-xpath-31-20161213] in a
   XML document.  For example, the JSON Path to select the value of the
   ASCII name inside an RDAP domain object is "$.ldhName", whereby $
   identifies the root of the document (DOM).  Another way to select a
   value inside a JSON document is the JSON Pointer [RFC6901].  While
   JSON Path or JSON Pointer are both standard ways to select any value
   inside JSON data, neither is particularly easy to use (e.g.
   "$.events[?(@.eventAction='registration')].eventDate" is the JSON
   Path expression of the registration date in an RDAP domain object).

   Therefore, this specification provides a definition of property-ref
   in terms of RDAP properties.  However, not all the RDAP properties
   are suitable to be used in sort criteria, such as:

   o  properties providing service information (e.g. links, notices,
      remarks, etc.);

   o  multivalued properties (e.g. status, roles, variants, etc.);

   o  properties modeling relationships to other objects (e.g.
      entities).

   On the contrary, some properties expressed as values of other
   properties (e.g. registration date) could be used in such a context.

   In the following, a list of properties an RDAP server MAY implement
   is presented.  The properties are divided into two groups: object
   common properties and object specific properties.

   o  Object common properties.  Object common properties are derived
      from the merge of the "eventAction" and the "eventDate"
      properties.  The following values of the "sort" parameter are
      defined:

      *  registrationDate
      *  reregistrationDate
      *  lastChangedDate
      *  expirationDate
      *  deletionDate
      *  reinstantiationDate
      *  transferDate
      *  lockedDate
      *  unlockedDate

   o  Object specific properties.  With regard to the specific
      properties, some of them are already defined among the query
      paths.  In the following a list of possible sorting properties,
      grouped by objects, is shown:

      *  Domain: name
      *  Nameserver: name, ipV4, ipV6.
      *  Entity: fn, handle, org, email, voice, country, cc, city.

   The correspondence between the sorting properties and the RDAP fields
   is shown in Table 1:

   +-----------+-----------+---------------------+------+-------+------+
   | Object    | Sorting   | RDAP property       | RFC  | RFC   | RFC  |
   | class     | property  |                     | 7483 | 6350  | 8605 |
   +-----------+-----------+---------------------+------+-------+------+
   | Searchabl | Common pr | eventAction values  | 4.5. |       |      |
   | e objects | operties  | suffixed by "Date"  |      |       |      |
   |           |           |                     |      |       |      |
   | Domain    | name      | unicodeName/ldhName | 5.3. |       |      |
   |           |           |                     |      |       |      |
   | Nameserve | name      | unicodeName/ldhName | 5.2. |       |      |
   | r         |           |                     |      |       |      |
   |           | ipV4      | v4 ipAddress        | 5.2. |       |      |
   |           | ipV6      | v6 ipAddress        | 5.2. |       |      |
   |           |           |                     |      |       |      |
   | Entity    | handle    | handle              | 5.1. |       |      |
   |           | fn        | vcard fn            | 5.1. | 6.2.1 |      |
   |           | org       | vcard org           | 5.1. | 6.6.4 |      |
   |           | voice     | vcard tel with      | 5.1. | 6.4.1 |      |
   |           |           | type="voice"        |      |       |      |
   |           | email     | vcard email         | 5.1. | 6.4.2 |      |
   |           | country   | country name in     | 5.1. | 6.3.1 |      |
   |           |           | vcard adr           |      |       |      |
   |           | cc        | country code in     | 5.1. |       | 3.1  |
   |           |           | vcard adr           |      |       |      |
   |           | city      | locality in vcard   | 5.1. | 6.3.1 |      |
   |           |           | adr                 |      |       |      |
   +-----------+-----------+---------------------+------+-------+------+

                  Table 1: Sorting properties definition

   With regard to the definitions in Table 1, some further
   considerations must be made to disambiguate some cases:

   o  since the response to a search on either domains or nameservers
      might include both A-labels and U-labels ([RFC5890]) in general, a
      consistent sorting policy shall take unicodeName and ldhName as
      two formats of the same value rather than separately.  Therefore,
      the unicodeName value MUST be taken while sorting, when
      unicodeName is missing, the value of ldhName MUST be considered
      instead;

   o  the jCard "sort-as" parameter MUST be ignored for the purpose of
      the sorting capability as described in this document;

   o  even if a nameserver can have multiple IPv4 and IPv6 addresses,
      the most common configuration includes one address for each IP
      version.  Therefore, the assumption of having a single IPv4 and/or
      IPv6 value for a nameserver cannot be considered too stringent; stringent.
      When more than one address per IP version is reported, sorting
      MUST be applied to the first value;

   o  with the exception of handle values, all the sorting properties
      defined for entity objects can be multivalued according to the
      definition of vCard as given in RFC6350 [RFC6350].  When more than
      one value is reported, sorting will MUST be applied to the preferred
      value identified by the parameter pref="1".  If the pref parameter
      is missing, sorting will MUST be applied to the first value.

   Each RDAP provider MAY define other sorting properties than those
   shown in this document as well as it MAY map those sorting properties
   onto different locations.

   The "jsonPath" field in the "sorting_metadata" element is used to
   clarify the RDAP field the sorting property refers to.  The mapping
   between the sorting properties and the JSON Paths of the RDAP fields
   is shown in Table 2.  The JSON Paths are provided according to the
   Goessner v.0.8.0 specification ([GOESSNER-JSON-PATH]):

   +-------+-------------+---------------------------------------------+
   | Objec | Sorting     | JSON Path                                   |
   | t     | property    |                                             |
   | class |             |                                             |
   +-------+-------------+---------------------------------------------+
   | Searc | registratio | "$.domainSearchResults[*].events[?(@.eventA |
   | hable | nDate       | ction=="registration")].eventDate           |
   | objec |             |                                             |
   | ts    |             |                                             |
   |       | reregistrat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | ionDate     | ction=="reregistration")].eventDate         |
   |       | lastChanged | "$.domainSearchResults[*].events[?(@.eventA |
   |       | Date        | ction=="lastChanged")].eventDate            |
   |       | expirationD | "$.domainSearchResults[*].events[?(@.eventA |
   |       | ate         | ction=="expiration")].eventDate             |
   |       | deletionDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="deletion")].eventDate               |
   |       | reinstantia | "$.domainSearchResults[*].events[?(@.eventA |
   |       | tionDate    | ction=="reinstantiation")].eventDate        |
   |       | transferDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="transfer")].eventDate               |
   |       | lockedDate  | "$.domainSearchResults[*].events[?(@.eventA |
   |       |             | ction=="locked")].eventDate                 |
   |       | unlockedDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="unlocked")].eventDate               |
   |       |             |                                             |
   | Domai | name        | $.domainSearchResults[*].unicodeName        |
   | n     |             |                                             |
   |       |             |                                             |
   | Names | name        | $.nameserverSearchResults[*].unicodeName    |
   | erver |             |                                             |
   |       | ipV4        | $.nameserverSearchResults[*].ipAddresses.v4 |
   |       |             | [0]                                         |
   |       | ipV6        | $.nameserverSearchResults[*].ipAddresses.v6 |
   |       |             | [0]                                         |
   |       |             |                                             |
   | Entit | handle      | $.entitySearchResults[*].handle             |
   | y     |             |                                             |
   |       | fn          | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]="fn")][3]                                |
   |       | org         | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]="org")][3]                               |
   |       | voice       | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="tel" && @[1].type=="voice")][3]        |
   |       | email       | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="email")][3]                            |
   |       | country     | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][3][6]                           |
   |       | cc          | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][1].cc                           |
   |       | city        | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][3][3]                           |
   +-------+-------------+---------------------------------------------+

              Table 2: Sorting properties - JSON Path Mapping

2.3.2.  Representing Sorting Links

   An RDAP server MAY use the "links" array of the "sorting_metadata"
   element to provide ready-made references [RFC8288] to the available
   sort criteria (Figure 4).  Each link represents a reference to an
   alternate view of the results.

   {
     "rdapConformance": [
       "rdap_level_0",
       "sorting_level_0"
     ],
     ...
     "sorting_metadata": {
        "currentSort": "name",
        "availableSorts": [
        {
        "property": "registrationDate",
        "jsonPath": "$.domainSearchResults[*]
           .events[?(@.eventAction==\"registration\")].eventDate",
        "default": false,
        "links": [
           {
           "value": "https://example.com/rdap/domains?name=*nr.com
                     &sort=name",
           "rel": "alternate",
           "href": "https://example.com/rdap/domains?name=*nr.com
                    &sort=registrationDate",
           "title": "Result Ascending Sort Link",
           "type": "application/rdap+json"
           },
           {
           "value": "https://example.com/rdap/domains?name=*nr.com
                     &sort=name",
           "rel": "alternate",
           "href": "https://example.com/rdap/domains?name=*nr.com
                    &sort=registrationDate:d",
           "title": "Result Descending Sort Link",
           "type": "application/rdap+json"
           }
        ],
        ...
     },
     "domainSearchResults": [
       ...
     ]
   }

      Figure 4: Example of a "sorting_metadata" instance to implement
                              result sorting

2.4.  "cursor" Parameter

   An RDAP query could return a response with hundreds, even thousands,
   of objects, especially when partial matching is used.  For that
   reason, the

   The cursor parameter addressing result pagination is defined in this specification can be used to make responses easier to handle.

   Presently, the most popular methods to implement
   encode information about any pagination method.  For example, in REST
   API are: the
   case of a simple implementation of the cursor parameter to represent
   offset pagination and keyset pagination.  Both two
   pagination methods don't require information, the server to handle cursor value
   "b2Zmc2V0PTEwMCxsaW1pdD01MAo=" is the result set mere Base64 encoding of
   "offset=100,limit=50".  Likewise, in a storage area across the requests since a new result set is
   generated each time a request is submitted.  Therefore, they are
   preferred in comparison simple implementation to any other method requiring
   represent keyset pagination information, the management
   of a REST session.

   Using limit and offset operators cursor value
   "a2V5PXRoZWxhc3Rkb21haW5vZnRoZXBhZ2UuY29t=" represents the traditionally used
   method to implement results pagination.  Both mere
   Base64 encoding of them can be used
   individually:

   o  "limit": means that "key=thelastdomainofthepage.com" whereby the server must return key
   value identifies the first N objects last row of the result set;

   o  "offset": means that the server must skip the first N objects and
      must return objects starting from position N+1.

   When limit and offset are used together, they allow current page.

   This solution lets RDAP providers to identify implement a
   specific portion of the result set.  For example, pagination method
   according to their needs, the pair
   "offset=100,limit=50" returns first 50 objects starting from position
   101 of user access levels, the result set.

   Despite its easiness of implementation, offset pagination raises some
   well known drawbacks:

   o  when offset has a very high value, scrolling submitted
   queries.  In addition, servers can change the result set could
      take some time;

   o  it always requires method over time
   without announcing anything to fetch all the rows before dropping as many
      rows as specified by offset;

   o  it may return inconsistent pages when data are frequently updated
      (i.e. real-time data) but this doesn't seem the case of
      registration data. clients.  The keyset pagination [SEEK] consists in adding a query condition considerations that enables the selection of the only data not yet returned.  This
   method
   has been taken as the basis for the implementation of a
   "cursor" parameter [CURSOR] by some REST API providers (e.g.
   [CURSOR-API1],[CURSOR-API2]). led to this solution are reported in more detail in Appendix A.

   The ABNF syntax of the cursor paramter is an opaque URL-safe
   string representing a logical pointer to the first result following:

      cursor = "cursor=" 1*( ALPHA / DIGIT / "/" / "=" / "-" / "_" )

   https://example.com/rdap/domains?name=*nr.com
   &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=

    Figure 5: An example of RDAP query reporting the "cursor" parameter

2.4.1.  Representing Paging Links

   An RDAP server SHOULD use the "links" array of the "paging_metadata"
   element to provide a ready-made reference [RFC8288] to the next page
   of the result set (Figure 5).

   Nevertheless, even keyset 6).  Examples of additional "rel" values a
   server MAY implements are "first", "last", "prev".

   {
     "rdapConformance": [
       "rdap_level_0",
       "paging_level_0"
     ],
     ...
     "notices": [
       {
         "title": "Search query limits",
         "type": "result set truncated due to excessive load",
         "description": [
         "search results for domains are limited to 50"
         ]
       }
     ],
     "paging_metadata": {
       "totalCount": 73,
       "pageSize": 50,
       "pageNumber": 1,
       "links": [
         {
         "value": "https://example.com/rdap/domains?name=*nr.com",
         "rel": "next",
         "href": "https://example.com/rdap/domains?name=*nr.com
                 &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=",
         "title": "Result Pagination Link",
         "type": "application/rdap+json"
         }
       ]
     },
     "domainSearchResults": [
       ...
     ]
   }

   Figure 6: Example of a "paging_metadata" instance to implement cursor
                                pagination can be troublesome:

   o  it needs at least one key field;

   o  it does not allow

2.4.2.  Paging Responses to sort just POST Requests

   In this specification, pagination is implemented by any field because providing the sorting
      criterion must contain a key;

   o  it works best
   user with full composite values support by DBMS (i.e.
      [x,y]>[a,b]), emulation is possible but ugly and less performant;

   o  it does a web link through a GET request [RFC7482].  However, GET
   could not allow to directly navigate to arbitrary pages because
      the result set must be scrolled in sequential order starting from the initial page;

   o  implementing only request method supported by an RDAP server in
   the bi-directional navigation is tedious because all
      comparison and sort operations have to future.

   A possible use case requiring POST might be reversed.

   Furthermore, in the RDAP context, some additional considerations can
   be made:

   o  an RDAP object is a conceptual aggregation submission of information
      generally collected from more than one data structure (e.g. table)
      and this makes even harder for a
   complex search condition including predicates joined by boolean
   operators (i.e.  OR, AND, NOT).  According to the developers search format and
   complexity, the implementation solution of providing a link by GET seems to be
   pretty inefficient.  In fact, GET isn't suitable for supporting
   either very long or URL-unsafe query strings.  It would be much more
   appropriate to send the keyset pagination that search pattern and the optional query
   parameters by POST.  Therefore, an RDAP response element which is already quite difficult.  For
      example,
   meant to represent the entity object can gather pagination information from different
      data structures (registrars, registrants, contacts, resellers, and
      so on), each one with its own key field mapping should also consider
   the RDAP entity
      handle;

   o  depending on POST method.

   As a consequence, the number of "paging_metadata" element MUST include an
   additional property, alternate to "links", that contains the page results as well cursor
   values used for pagination.  Such property is defined as in the number
      and the complexity
   following:

      "cursors": "String[String]" (OPTIONAL) a map of cursor values
      pointing to specific fixed size portions of the properties result set.  Ths
      property MUST be used instead of each RDAP object in "links" when the
      response, request is
      submitted via POST.  The map keys MUST contain the time required by offset pagination "rel" values
      used for generating the paging links (Figure 7).  Examples are:
      "next", "prev", "last".  The link to skip the
      previous pages could be much faster than the processing time
      needed first page is
      unnecessary.

   {
     "rdapConformance": [
       "rdap_level_0",
       "paging_level_0"
     ],
     ...
     "notices": [
       {
         "title": "Search query limits",
         "type": "result set truncated due to build the current page.  In fact, RDAP objects excessive load",
         "description": [
         "search results for domains are
      usually formed by information belonging limited to multiple data
      structures and containing multivalued properties (i.e. arrays)
      and, therefore, data selection might be 50"
         ]
       }
     ],
     "paging_metadata": {
       "totalCount": 73,
       "pageSize": 50,
       "pageNumber": 1,
       "cursors": {
         "next":"wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M="
       }
     },
     "domainSearchResults": [
       ...
     ]
   }

   Figure 7: Example of a time consuming process.
      This situation occurs even though "paging_metadata" instance when the selection request is supported by
      indexes;

   o  depending on
                            submitted via POST

3.  Negative Answers

   The value constraints for the access levels parameters are defined by their ABNF
   syntax.  Therefore, each RDAP operator, the
      increase of complexity and the decrease of flexibility of keyset
      pagination with respect to the offset pagination could request including an invalid value for a
   parameter SHOULD obtain an HTTP 400 (Bad Request) response code.  The
   same response SHOULD be
      considered impractical.

   Ultimately, returned in the following cases:

   o  if in both pagination methods have benefits single and drawbacks.

   That said, multi sort the cursor client provides an
      unsupported value for the "sort" parameter defined in this specification can be
   used as well as a value
      related to encode information about any pagination method.  For example, an object property not included in the case of a simple implementation of the cursor parameter to
   represent offset pagination information, response;

   o  if the cursor client submits an invalid value
   "b2Zmc2V0PTEwMCxsaW1pdD01MAo=" is for the mere Base64 encoding of
   "offset=100,limit=50".  Likewise, in a simple implementation to
   represent keyset pagination information, the cursor value
   "a2V5PXRoZWxhc3Rkb21haW5vZnRoZXBhZ2UuY29t=" represents the mere
   Base64 encoding of "key=thelastdomainofthepage.com" whereby "cursor" parameter.

   Optionally, the key
   value identifies response MAY include additional information regarding
   the last row of negative answer in the current page.

   This solution lets HTTP entity body.

4.  RDAP providers to implement a pagination method
   according to their needs, Conformance

   Servers returning the user access levels, "paging_metadata" element in their response
   MUST include "paging_level_0" in the submitted
   queries.  In addition, rdapConformance array as well as
   servers can change the method over time
   without announcing anything to returning the clients. "sorting_metadata" element MUST include
   "sorting_level_0".

5.  Implementation Considerations

   The ABNF syntax implementation of the cursor paramter new parameters is technically feasible, as
   operators for counting, sorting and paging are currently supported by
   the following:

      cursor = "cursor=" 1*( ALPHA / DIGIT / "/" / "=" / "-" / "_" )

   https://example.com/rdap/domains?name=*nr.com
   &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=

    Figure 5: An example of RDAP query reporting major RDBMSs.

   Similar operators are completely or partially supported by the "cursor" parameter

2.4.1.  Representing Paging Links

   An RDAP server SHOULD use most
   known NoSQL databases (MongoDB, CouchDB, HBase, Cassandra, Hadoop) so
   the "links" array implementation of the "paging_metadata"
   element new parameters seems to provide a ready-made be practicable by
   servers working without the use of an RDBMS.

6.  Implementation Status

   NOTE: Please remove this section and the reference [RFC8288] to RFC 7942 prior
   to publication as an RFC.

   This section records the next page status of known implementations of the result set (Figure 6).  Examples
   protocol defined by this specification at the time of additional "rel" values posting of this
   Internet-Draft, and is based on a
   server MAY implements are "first", "last", "prev".

   {
     "rdapConformance": [
       "rdap_level_0",
       "paging_level_0"
     ],
     ...
     "notices": [
       {
         "title": "Search query limits",
         "type": "result set truncated due to excessive load",
         "description": [
         "search results for domains are limited to 50"
         ]
       }
     ],
     "paging_metadata": {
       "totalCount": 73,
       "pageSize": 50,
       "pageNumber": 1,
       "links": [
         {
         "value": "https://example.com/rdap/domains?name=*nr.com",
         "rel": "next",
         "href": "https://example.com/rdap/domains?name=*nr.com
                 &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=",
         "title": "Result Pagination Link",
         "type": "application/rdap+json"
         }
       ]
     },
     "domainSearchResults": [
       ...
     ]
   }

   Figure 6: Example proposal described in RFC 7942
   [RFC7942].  The description of a "paging_metadata" instance to implement cursor
                                pagination

2.4.2.  Paging Responses to POST Requests

   In implementations in this specification, pagination section is implemented by providing the
   user with a web link through a GET request [RFC7482].  However, GET
   could not be
   intended to assist the only request method supported by an RDAP server IETF in
   the future.

   A possible use case requiring POST might be the submission of a
   complex search condition including predicates joined by boolean
   operators (i.e.  OR, AND, NOT).  According its decision processes in progressing
   drafts to RFCs.  Please note that the search format and
   complexity, the solution listing of providing a link any individual
   implementation here does not imply endorsement by GET seems to be
   pretty inefficient.  In fact, GET isn't suitable for supporting
   either very long or URL-unsafe query strings.  It would be much more
   appropriate to send the search pattern and IETF.
   Furthermore, no effort has been spent to verify the optional query
   parameters information
   presented here that was supplied by POST.  Therefore, an RDAP response element which IETF contributors.  This is
   meant not
   intended as, and must not be construed to represent the pagination information should also consider
   the POST method.

   As be, a consequence, the "paging_metadata" element MUST include an
   additional property, alternate catalog of available
   implementations or their features.  Readers are advised to "links", note that contains
   other implementations may exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the cursor
   values used for pagination.  Such property is defined benefit of
   running code, which may serve as in the
   following:

      "cursors": "String[String]" (OPTIONAL) a map evidence of cursor values
      pointing valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to specific fixed size portions of the result set.  Ths
      property MUST be used instead individual working groups to use this information as
   they see fit".

6.1.  IIT-CNR/Registro.it

      Responsible Organization: Institute of "links" when the request Informatics and Telematics
      of National Research Council (IIT-CNR)/Registro.it
      Location: https://rdap.pubtest.nic.it/
      Description: This implementation includes support for RDAP queries
      using data from .it public test environment.
      Level of Maturity: This is
      submitted via POST.  The map keys MUST contain an "alpha" test implementation.
      Coverage: This implementation includes all of the "rel" values
      used features
      described in this specification.
      Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it

6.2.  Google Registry

      Responsible Organization: Google Registry
      Location: https://www.registry.google/rdap/
      Description: This implementation includes support for generating the paging links (Figure 7).  Examples are:
      "next", "prev", "last". RDAP queries
      for TLDs such as .google, .how, .soy, and others.  The RDAP server
      implements cursor pagination.  The link used to request the first next
      page is
      unnecessary.

   {
     "rdapConformance": [
       "rdap_level_0",
       "paging_level_0"
     ],
     ...
     "notices": [
       {
         "title": "Search query limits",
         "type": "result set truncated due to excessive load",
         "description": [
         "search results for domains are limited to 50"
         ]
       }
     ],
     "paging_metadata": {
       "totalCount": 73,
       "pageSize": 50,
       "pageNumber": 1,
       "cursors": {
         "next":"wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M="
       }
     },
     "domainSearchResults": [
       ...
     ]
   }

   Figure 7: Example of a "paging_metadata" instance when the request is
                            submitted via POST

3.  Negative Answers

   The value constraints for the parameters are defined by their ABNF
   syntax.  Therefore, each request including an invalid value for a
   parameter SHOULD obtain an HTTP 400 (Bad Request) response code.  The
   same response SHOULD be returned included in the following cases:

   o  if notice section of the client provides an unsupported value for response.
      Level of Maturity: Production.
      Coverage: This implementation includes the "sort" "cursor" parameter
      described in both single and multi sort;

   o  if the client submits an invalid value for the "cursor" parameter.

   Optionally, the response MAY include additional information regarding this specification.
      Contact Information: Brian Mountford, mountford@google.com

7.  IANA Considerations

   IANA is requested to register the negative answer following values in the HTTP entity body.

4. RDAP Conformance

   Servers returning
   Extensions Registry:

      Extension identifier: paging
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice for
      result set paging.

      Extension identifier: sorting
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice for
      result set sorting.

8.  Security Considerations

   Security services for the "paging_metadata" element operations specified in their response
   MUST include "paging_level_0" this document are
   described in the rdapConformance array as well as
   servers returning the "sorting_metadata" element MUST include
   "sorting_level_0".

5.  Implementation Considerations RFC 7481 [RFC7481].

   The implementation of the new parameters is technically feasible, search query typically requires more server resources (such as
   operators for counting, sorting
   memory, CPU cycles, and paging are currently supported by
   the major RDBMSs.

   Similar operators are completely or partially supported by network bandwidth) when compared to the most
   known NoSQL databases (MongoDB, CouchDB, HBase, Cassandra, Hadoop) so
   lookup query.  This increases the implementation risk of the new parameters seems server resource exhaustion
   and subsequent denial of service due to abuse.  This risk can be practicable
   mitigated by
   servers working without either restricting search functionality and limiting the use
   rate of an RDBMS.

6.  Implementation Status

   NOTE: Please remove search requests.  Servers can also reduce their load by
   truncating the results in the response.  However, this section and last security
   policy can result in a higher inefficiency if the reference RDAP server does
   not provide any functionality to RFC 7942 prior return the truncated results.

   The new parameters presented in this document provide the RDAP
   operators with a way to publication as an RFC.

   This section records implement a secure server without penalizing
   its efficiency.  The "count" parameter gives the status of known implementations of user a measure to
   evaluate the
   protocol defined by this specification query precision and, at the time of posting of this
   Internet-Draft, and is based on same time, returns a proposal described in RFC 7942
   [RFC7942].
   significant information.  The description of implementations in this section is
   intended to assist "sort" parameter allows the IETF in its decision processes in progressing
   drafts user to RFCs.  Please note that
   obtain the listing most relevant information at the beginning of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify result
   set.  In both cases, the information
   presented here that was supplied by IETF contributors.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to RFC 7942, "this will allow reviewers and working groups user doesn't need to assign due consideration submit further
   unnecessary search requests.  Finally, the "cursor" parameter enables
   the user to documents that have scroll the benefit of
   running code, which may serve as evidence result set by submitting a sequence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up
   sustainable queries according to the individual working groups server limits.

9.  Acknowledgements

   The authors would like to use this information as
   they see fit".

6.1.  IIT-CNR/Registro.it

      Responsible Organization: Institute of Informatics acknowledge Brian Mountford and Telematics
      of National Research Council (IIT-CNR)/Registro.it
      Location: https://rdap.pubtest.nic.it/
      Description: This implementation includes support Tom
   Harrison for RDAP queries
      using data from .it public test environment.
      Level of Maturity: This is a "proof of concept" research
      implementation.
      Coverage: This implementation includes all of their contribution to the features
      described in development of this specification.
      Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it

6.2.  Google Registry

      Responsible Organization: Google Registry
      Location: https://www.registry.google/rdap/
      Description: This implementation includes support document.

10.  References

10.1.  Normative References

   [ISO.3166.1988]
              International Organization for RDAP queries Standardization, "Codes for TLDs such as .google, .how, .soy, and others.  The RDAP server
      implements cursor pagination.  The link used to request the next
      page is included in
              the notice section representation of the response.
      Level names of Maturity: Production.
      Coverage: This implementation includes the "cursor" parameter
      described countries, 3rd edition",
              ISO Standard 3166, August 1988.

   [RFC2119]  Bradner, S., "Key words for use in this specification.
      Contact Information: Brian Mountford, mountford@google.com

7.  IANA Considerations

   IANA is requested RFCs to register the following values in the RDAP
   Extensions Registry:

      Extension identifier: paging
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice for
      result set paging.

      Extension identifier: sorting
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for
      result set sorting.

8.  Security Writing an
              IANA Considerations

   Security services for the operations specified in this document are
   described Section in RFCs", RFC 7481 [RFC7481].

   The search query typically requires more server resources (such as
   memory, CPU cycles, 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5234]  Crocker, D., Ed. and network bandwidth) when compared to the
   lookup query.  This increases the risk of server resource exhaustion P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and subsequent denial of service due to abuse.  This risk can be
   mitigated by either restricting search functionality Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <https://www.rfc-editor.org/info/rfc5890>.

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              DOI 10.17487/RFC6350, August 2011,
              <https://www.rfc-editor.org/info/rfc6350>.

   [RFC7230]  Fielding, R., Ed. and limiting the
   rate of search requests.  Servers can also reduce their load by
   truncating the results in the response.  However, this last security
   policy can result in a higher inefficiency if the RDAP server does
   not provide any functionality to return the truncated results.

   The new parameters presented J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in this document provide the RDAP
   operators with a way to implement a secure server without penalizing
   its efficiency.  The "count" parameter gives the user a measure to
   evaluate the query precision and, at the same time, returns a
   significant information.  The "sort" parameter allows the user to
   obtain the most relevant information at the beginning of the result
   set.  In both cases, the user doesn't need to submit further
   unnecessary search requests.  Finally, the "cursor" parameter enables
   the user to scroll the result set by submitting a sequence of
   sustainable queries according to the server limits.

9.  Acknowledgements

   The authors would like to acknowledge Brian Mountford
              Registration Data Access Protocol (RDAP)", RFC 7480,
              DOI 10.17487/RFC7480, March 2015,
              <https://www.rfc-editor.org/info/rfc7480>.

   [RFC7481]  Hollenbeck, S. and Tom
   Harrison for their contribution to the development of this document.

10.  References

10.1.  Normative References

   [ISO.3166.1988]
              International Organization for Standardization, "Codes N. Kong, "Security Services for the representation of names of countries, 3rd edition",
              ISO Standard 3166, August 1988.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14,
              Registration Data Access Protocol (RDAP)", RFC 2119, 7481,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <https://www.rfc-editor.org/info/rfc5890>.

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              DOI 10.17487/RFC6350, August 2011,
              <https://www.rfc-editor.org/info/rfc6350>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
              Registration Data Access Protocol (RDAP)", RFC 7480,
              DOI 10.17487/RFC7480, March 2015,
              <https://www.rfc-editor.org/info/rfc7480>.

   [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the
              Registration Data Access Protocol (RDAP)", RFC 7481,
              DOI 10.17487/RFC7481, 10.17487/RFC7481, March 2015,
              <https://www.rfc-editor.org/info/rfc7481>.

   [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482,
              DOI 10.17487/RFC7482, March 2015,
              <https://www.rfc-editor.org/info/rfc7482>.

   [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", RFC 7483,
              DOI 10.17487/RFC7483, March 2015,
              <https://www.rfc-editor.org/info/rfc7483>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.

   [RFC8605]  Hollenbeck, S. and R. Carney, "vCard Format Extensions:
              ICANN Extensions for the Registration Data Access Protocol
              (RDAP)", RFC 8605, DOI 10.17487/RFC8605, May 2019,
              <https://www.rfc-editor.org/info/rfc8605>.

10.2.  Informative References

   [CURSOR]   Nimesh, R., "Paginating Real-Time Data with Keyset
              Pagination", July 2014, <https://www.sitepoint.com/
              paginating-real-time-data-cursor-based-pagination/>.

   [CURSOR-API1]
              facebook.com, "facebook for developers - Using the Graph
              API", July 2017, <https://developers.facebook.com/docs/
              graph-api/using-graph-api>.

   [CURSOR-API2]
              twitter.com, "Pagination", 2017,
              <https://developer.twitter.com/en/docs/ads/general/guides/
              pagination.html>.

   [GOESSNER-JSON-PATH]
              Goessner, S., "JSONPath - XPath for JSON", 2007,
              <http://goessner.net/articles/JsonPath/>.

   [HATEOAS]  Jedrzejewski, B., "HATEOAS - a simple explanation", 2018,
              <https://www.e4developer.com/2018/02/16/hateoas-simple-
              explanation/>.

   [OData-Part1]
              Pizzo, M., Handl, R., and M. Zurmuehl, "OData Version 4.0.
              Part 1: Protocol Plus Errata 03", June 2016,
              <http://docs.oasis-
              open.org/odata/odata/v4.0/errata03/os/complete/part1-
              protocol/odata-v4.0-errata03-os-part1-protocol-
              complete.pdf>.

   [REST]     Fredrich, T., "RESTful Service Best Practices,
              Recommendations for Creating Web Services", April 2012,
              <http://www.restapitutorial.com/media/
              RESTful_Best_Practices-v1_1.pdf>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7942]  Sheffer, Y. M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [SEEK]     EverSQL.com, "Faster Pagination in Mysql - Why Order By
              With Limit and Offset is Slow?", July 2017,
              <https://www.eversql.com/faster-pagination-in-mysql-why-
              order-by-with-limit-and-offset-is-slow/>.

   [W3C.CR-xpath-31-20161213]
              Robie, J., Dyck, M., and J. Spiegel, "XML Path Language
              (XPath) 3.1", World Wide Web Consortium CR CR-xpath-
              31-20161213, December 2016,
              <https://www.w3.org/TR/2016/CR-xpath-31-20161213>.

Appendix A.  Approaches to Result Pagination

   An RDAP query could return a response with hundreds, even thousands,
   of objects, especially when partial matching is used.  For that
   reason, the cursor parameter addressing result pagination is defined
   to make responses easier to handle.

   Presently, the most popular methods to implement pagination in REST
   API are: offset pagination and keyset pagination.  Both two
   pagination methods don't require the server to handle the result set
   in a storage area across the requests since a new result set is
   generated each time a request is submitted.  Therefore, they are
   preferred in comparison to any other method requiring the management
   of a REST session.

   Using limit and offset operators represents the traditionally used
   method to implement results pagination.  Both of them can be used
   individually:

   o  "limit": means that the server must return the first N objects of
      the result set;

   o  "offset": means that the server must skip the first N objects and
      must return objects starting from position N+1.

   When limit and offset are used together, they allow to identify a
   specific portion of the result set.  For example, the pair
   "offset=100,limit=50" returns first 50 objects starting from position
   101 of the result set.

   Despite its easiness of implementation, offset pagination raises some
   well known drawbacks:

   o  when offset has a very high value, scrolling the result set could
      take some time;

   o  it always requires to fetch all the rows before dropping as many
      rows as specified by offset;

   o  it may return inconsistent pages when data are frequently updated
      (i.e. real-time data) but this doesn't seem the case of
      registration data.

   The keyset pagination [SEEK] consists in adding a query condition
   that enables the selection of the only data not yet returned.  This
   method has been taken as the basis for the implementation of a
   "cursor" parameter [CURSOR] by some REST API providers (e.g.
   [CURSOR-API1],[CURSOR-API2]).  The cursor is an opaque URL-safe
   string representing a logical pointer to the first result of the next
   page (Figure 5).

   Nevertheless, even keyset pagination can be troublesome:

   o  it needs at least one key field;

   o  it does not allow to sort just by any field because the sorting
      criterion must contain a key;

   o  it works best with full composite values support by DBMS (i.e.
      [x,y]>[a,b]), emulation is possible but ugly and less performant;

   o  it does not allow to directly navigate to arbitrary pages because
      the result set must be scrolled in sequential order starting from
      the initial page;

   o  implementing the bi-directional navigation is tedious because all
      comparison and sort operations have to be reversed.

A.1.  Specific Issues Raised by RDAP

   Furthermore, in the RDAP context, some additional considerations can
   be made:

   o  an RDAP object is a conceptual aggregation of information
      generally collected from more than one data structure (e.g. table)
      and this makes even harder for the developers the implementation
      of the keyset pagination that is already quite difficult.  For
      example, the entity object can gather information from different
      data structures (registrars, registrants, contacts, resellers, and
      so on), each one with its own key field mapping the RDAP entity
      handle;

   o  depending on the number of the page results as well as the number
      and A. Farrel, "Improving Awareness the complexity of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [SEEK]     EverSQL.com, "Faster Pagination the properties of each RDAP object in Mysql - Why Order By
              With Limit the
      response, the time required by offset pagination to skip the
      previous pages could be much faster than the processing time
      needed to build the current page.  In fact, RDAP objects are
      usually formed by information belonging to multiple data
      structures and Offset containing multivalued properties (i.e. arrays)
      and, therefore, data selection might be a time consuming process.
      This situation occurs even though the selection is Slow?", July 2017,
              <https://www.eversql.com/faster-pagination-in-mysql-why-
              order-by-with-limit-and-offset-is-slow/>.

   [W3C.CR-xpath-31-20161213]
              Robie, J., Dyck, M., supported by
      indexes;

   o  depending on the access levels defined by each RDAP operator, the
      increase of complexity and J. Spiegel, "XML Path Language
              (XPath) 3.1", World Wide Web Consortium CR CR-xpath-
              31-20161213, December 2016,
              <https://www.w3.org/TR/2016/CR-xpath-31-20161213>. the decrease of flexibility of keyset
      pagination with respect to the offset pagination could be
      considered impractical.

   Ultimately, both pagination methods have benefits and drawbacks.

Appendix A. B.  Change Log

   00:  Initial working group version ported from draft-loffredo-regext-
      rdap-sorting-and-paging-05
   01:  Removed both "offset" and "nextOffset" to keep "paging_metadata"
      consistent between the pagination methods.  Renamed
      "Considerations about Paging Implementation" section in ""cursor"
      Parameter".  Removed "FOR DISCUSSION" items.  Provided a more
      detailed description of both "sorting_metadata" and
      "paging_metadata" elements.
   02:  Removed both "offset" and "limit" parameters.  Added ABNF syntax
      of cursor parameter.  Rearranged the layout of some sections.
      Removed some items from "Informative References" section.  Changed
      "IANA Considerations" section.
   03:  Added "cc" to the list of sorting properties in "Sorting
      Properties Declaration" section.  Added RFC8605 to the list of
      "Informative References".
   04:  Replaced "ldhName" with "name" in the "Sorting Properties
      Declaration" section.  Clarified the sorting logic with respect to
      the JSON value types and the sorting policy for multivalued
      fields.
   05:  Clarified the logic of sorting on IP addresses.  Clarified the
      mapping between the sorting properties and the RDAP fields.
      Updated "Acknowledgements" section.
   06:  Renamed "pageCount" to "pageSize" and added "pageNumber" in the
      "paging_metadata" element.
   07:  Added "Paging Responses to POST Requests" section.
   08:  Added "Approaches to Result Pagination" section in the appendix.
      Added the case of requesting a sort on a property not included in
      the response to the errors listed in the "Negative Answers"
      section .

Authors' Addresses

   Mario Loffredo
   IIT-CNR/Registro.it
   Via Moruzzi,1
   Pisa  56124
   IT

   Email: mario.loffredo@iit.cnr.it
   URI:   http://www.iit.cnr.it

   Maurizio Martinelli
   IIT-CNR/Registro.it
   Via Moruzzi,1
   Pisa  56124
   IT

   Email: maurizio.martinelli@iit.cnr.it
   URI:   http://www.iit.cnr.it

   Scott Hollenbeck
   Verisign Labs
   12061 Bluemont Way
   Reston, VA  20190
   USA

   Email: shollenbeck@verisign.com
   URI:   https://www.verisignlabs.com/