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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" xml:lang="en" submissionType="IETF"
category="std" consensus="true" docName="draft-ietf-regext-rdap-partial-response-16" ipr="trust200902">
number="8982" ipr="trust200902" tocInclude="true" tocDepth="4" sortRefs="true"
symRefs="true" version="3">

  <front>
    <title abbrev="RDAP Partial Response">Registration Data Access Protocol (RDAP) Partial Response</title>
    <seriesInfo name="RFC" value="8982"/>
    <author fullname="Mario Loffredo" initials="M." surname="Loffredo">
      <organization>IIT-CNR/Registro.it</organization>
      <address>
        <postal>
          <street>Via Moruzzi,1</street>
          <city>Pisa</city>
          <country>IT</country>
          <code>56124</code>
        </postal>
        <email>mario.loffredo@iit.cnr.it</email>
        <uri>http://www.iit.cnr.it</uri>
        <uri>https://www.iit.cnr.it</uri>
      </address>
    </author>
    <author fullname="Maurizio Martinelli" initials="M." surname="Martinelli">
      <organization>IIT-CNR/Registro.it</organization>
      <address>
        <postal>
          <street>Via Moruzzi,1</street>
          <city>Pisa</city>
          <country>IT</country>
          <code>56124</code>
        </postal>
        <email>maurizio.martinelli@iit.cnr.it</email>
        <uri>http://www.iit.cnr.it</uri>
        <uri>https://www.iit.cnr.it</uri>
      </address>
    </author>

    <date/>
    <date year="2021" month="February"/>
    <area>Applications and Real-Time</area>
    <workgroup>Registration Protocols Extensions</workgroup>
    <keyword>RDAP</keyword>
    <keyword>Partial response</keyword>
    <abstract>
      <t>The Registration Data Access Protocol (RDAP) does not include capabilities to request partial responses.  Servers will only return full responses that include all of the information that a client is authorized to receive.  A partial response capability that limits the amount of information returned, especially in the case of search queries, could bring benefits to both clients and servers.  This document describes an RDAP query extension that allows clients to specify their preference for obtaining a partial response.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction"  title="Introduction"> anchor="introduction">

      <name>Introduction</name>
      <t>The use of partial responses in RESTful API <xref
      target="REST"/> design is very common.  The rationale is quite simple:
      instead of returning objects in API responses with all data fields, only
      a subset of the fields in each result object is returned.  The benefit
      is obvious: less data transferred over the network means less bandwidth
      usage, faster server responses, less CPU time spent both on the server
      and the client, and less memory usage on the client.</t>

      <t>Currently, RDAP does not provide a client with any way to request a
      partial response.  Servers can only provide the client with a full
      response <xref target="RFC7483"/>.  Servers cannot limit the amount of
      information returned in a response based on a client's preferences, and
      this creates inefficiencies.</t>
      <t>The protocol described in this specification extends RDAP search
      capabilities to enable partial responses through the provisioning of pre-defined
      predefined sets of fields that clients can submit to an RDAP service by
      adding a new query parameter.  The service is implemented using the
      Hypertext Transfer Protocol (HTTP) <xref target="RFC7230"/> and the
      conventions described in <xref target="RFC7480"/>.</t>

      <section title="Conventions
      <section>
        <name>Conventions Used in This Document">
      	<t>The Document</name>

        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are
    to be interpreted as described in BCP 14 BCP&nbsp;14 <xref target="RFC2119"/>
    <xref target="RFC8174"/> when, and only when, they appear in all capitals,
    as shown here.</t> here.
        </t>

      </section>
    </section>
    <section anchor="rdap-path-segment-specification" title="RDAP anchor="rdap-path-segment-specification">
      <name>RDAP Path Segment Specification"> Specification</name>
      <t>The path segment defined in this section is an OPTIONAL
      <bcp14>OPTIONAL</bcp14> extension of search path segments defined in
      <xref target="RFC7482"/>.  This document defines an RDAP query
      parameter, &quot;fieldSet&quot;, "fieldSet", whose value is a non-empty string identifying a
      server-defined set of fields returned in place of the full response.
      The field sets supported by a server are usually described in
      out-of-band documents (e.g., RDAP profile) together with other features.
      Moreover, this document defines in <xref
      target="rdap-subsetting-metadata"/> an in-band mechanism by means of
      which servers can provide clients with a basic information about the
      supported field sets.</t>
      <t>The following is an example of an RDAP query including the &quot;fieldSet&quot; "fieldSet" parameter:</t>

        <t>https://example.com/rdap/domains?name=example*.com&amp;fieldSet=afieldset</t>
      <artwork><![CDATA[
https://example.com/rdap/domains?name=example*.com&fieldSet=afieldset
]]></artwork>
      <t>This solution can be implemented by RDAP providers with less effort
      than field selection and is easily requested by clients.  The
      considerations that have led to this solution are described in more
      detail in <xref
      target="approaches-to-partial-response-implementation"/>.</t>
      <section anchor="rdap-subsetting-metadata" title="Subsetting Metadata"> anchor="rdap-subsetting-metadata">

        <name>Subsetting Metadata</name>
        <t>According to most advanced principles in REST design, collectively
        known as HATEOAS (Hypermedia "Hypermedia as the Engine of Application State) State" (HATEOAS)
        <xref target="HATEOAS"/>, a client entering a REST application through
        an initial URI should use server-provided links to dynamically
        discover available actions and access the resources it needs.  In this
        way, the client is not required to have prior knowledge of the service and,
        nor, consequently, to hard code hard-code the URIs of different resources.  This
        allows the server to make URI changes as the API evolves without
        breaking clients.  Definitively, a REST service should be as
        self-descriptive as possible.</t>
        <t>Therefore, servers implementing the query parameter described in
        this specification SHOULD <bcp14>SHOULD</bcp14> provide additional
        information in their responses about the available field sets.  Such
        information is collected in a new JSON data structure named &quot;subsetting_metadata&quot;
        "subsetting_metadata" containing the following properties:</t>
        <t><list style="symbols">
	  <t>&quot;currentFieldSet&quot;: &quot;String&quot; (REQUIRED) either
<dl newline="true">

<dt>"currentFieldSet": "String" (<bcp14>REQUIRED</bcp14>)
</dt>
<dd>either the value of the &quot;fieldSet&quot; "fieldSet" parameter as specified in the query
string, or the field set applied by default;<vspace blankLines='1'/></t>
	  <t>&quot;availableFieldSets&quot;: &quot;AvailableFieldSet[]&quot;  (OPTIONAL) an default.
</dd>

<dt>"availableFieldSets": "AvailableFieldSet[]"  (<bcp14>OPTIONAL</bcp14>)
</dt>
<dd><t>an array of objects, with each element describing an available field set.
The AvailableFieldSet object includes the following members:
          <list style="symbols">
	     <t>&quot;name&quot;: &quot;String&quot; (REQUIRED) the field set name;</t>
          <t>&quot;default&quot;: &quot;Boolean&quot; (REQUIRED) members:</t>

<dl newline="true">

<dt>"name": "String" (<bcp14>REQUIRED</bcp14>)
</dt>
<dd>the field set name.
</dd>

<dt>"default": "Boolean" (<bcp14>REQUIRED</bcp14>)
</dt>
<dd>indicator of whether the field set is applied by
default.  An RDAP server MUST <bcp14>MUST</bcp14> define only one default field set;</t>
          <t>&quot;description&quot;: &quot;String&quot;  (OPTIONAL) a set.
</dd>

<dt>"description": "String"  (<bcp14>OPTIONAL</bcp14>)
</dt>
<dd>a human-readable description of the field set;</t>
	  <t>&quot;links&quot;: &quot;Link[]&quot; (OPTIONAL) an set.
</dd>

<dt>"links": "Link[]" (<bcp14>OPTIONAL</bcp14>)
</dt>
<dd>an array of links as described in <xref target="RFC8288"/> containing the
query string that applies the field set (see <xref target="subsetting_links"/>).</t>
	  </list></t>
	</list></t>
target="subsetting_links"/>).
</dd>
</dl>

</dd>
</dl>

        <section anchor="rdap-conformance" title="RDAP Conformance"> anchor="rdap-conformance">
          <name>RDAP Conformance</name>
          <t>Servers returning the &quot;subsetting_metadata&quot; "subsetting_metadata" section in their responses MUST <bcp14>MUST</bcp14> include &quot;subsetting&quot; "subsetting" in the rdapConformance array.</t>
        </section>
        <section anchor="subsetting_links" title="Representing anchor="subsetting_links">
          <name>Representing Subsetting Links"> Links</name>
          <t>An RDAP server MAY <bcp14>MAY</bcp14> use the &quot;links&quot; "links" array of the &quot;subsetting_metadata&quot; "subsetting_metadata" element to provide ready-made references <xref target="RFC8288"/> to the available field sets (<xref target="subset-link-in-response-example"/>).  The target URI in each link is the reference to an alternative to the current view of results identified by the context URI.</t>
          <t>The &quot;value&quot;, &quot;rel&quot; "value", "rel", and &quot;href&quot; "href" JSON values MUST <bcp14>MUST</bcp14> be specified.  All other JSON values are OPTIONAL.</t> <bcp14>OPTIONAL</bcp14>.</t>
          <figure anchor="subset-link-in-response-example" title="Example anchor="subset-link-in-response-example">
            <name>Example of a &quot;subsetting_metadata&quot; instance">
        <artwork xml:space="preserve"><![CDATA[ "subsetting_metadata" Instance</name>

<sourcecode type="json"><![CDATA[
{
  "rdapConformance": [
    "rdap_level_0",
    "subsetting"
  ],
  ...
  "subsetting_metadata": {
    "currentFieldSet": "afieldset",
    "availableFieldSets": [
      {
      "name": "anotherfieldset",
      "description": "Contains some fields",
      "default": false,
      "links": [
        {
        "value": "https://example.com/rdap/domains?name=example*.com
                  &fieldSet=afieldset",
        "rel": "alternate",
        "href": "https://example.com/rdap/domains?name=example*.com
                 &fieldSet=anotherfieldset",
        "title": "Result Subset Link",
        "type": "application/rdap+json"
        }
      ]
      },
    ...
    ]
  },
  ...
  "domainSearchResults": [
    ...
  ]
}
        ]]></artwork>
]]></sourcecode>
          </figure>
        </section>
      </section>
    </section>
    <section anchor="rdap-field-set-relationships" title="Dealing anchor="rdap-field-set-relationships">
      <name>Dealing with Relationships"> Relationships</name>
      <t>Representation of second level second-level objects within a field set produces additional considerations.  Since the representation of the topmost returned objects will vary according to the field set in use, the response may contain no relationships (e.g., for an abbreviated field set) or may contain associated objects as in a normal RDAP query response.  Each field set can indicate the format of the additional objects to be returned, in the same manner that the format of the topmost objects is controlled by the field set.</t>
    </section>
    <section anchor="basic-field-sets" title="Basic anchor="basic-field-sets">
      <name>Basic Field Sets"> Sets</name>
      <t>This section defines three basic field sets which that servers MAY
      <bcp14>MAY</bcp14> implement to facilitate their interaction with
      clients:</t>

        <t><list style="symbols">
	  <t>&quot;id&quot;: the

<dl>

<dt>"id":
</dt>
<dd>The server provides only the key field: &quot;handle&quot; field; "handle" for entities, &quot;ldhName&quot; and "ldhName" for domains
and nameservers.  If a returned domain or nameserver is an Internationalized Domain Name (IDN) <xref
target="RFC5890"/>, then the &quot;unicodeName&quot; "unicodeName" field MUST <bcp14>MUST</bcp14> additionally be included in the
response.  This field set could be used when the client wants to obtain a collection of object
identifiers (<xref target="fieldSet-id-response-example"/>);<vspace blankLines='1' /></t>
	  <t>&quot;brief&quot;: the target="fieldSet-id-response-example"/>).
</dd>

<dt>"brief":
</dt>
<dd>The field set contains the fields that can be included in a &quot;short&quot; "short" response.
This field set could be used when the client is asking for a subset of the full response which that provides
only basic knowledge of each object;<vspace blankLines='1'/></t>
	  <t>&quot;full&quot;: the object.
</dd>

<dt>"full":
</dt>
<dd>The field set contains all of the information the server can provide for a
particular object.</t>
	</list></t> object.
</dd>

</dl>

      <t>The &quot;objectClassName&quot; "objectClassName" field is implicitly included in each of the above field sets.  RDAP providers SHOULD <bcp14>SHOULD</bcp14> include a &quot;links&quot; "links" field indicating the &quot;self&quot; "self" link relationship.  RDAP providers MAY <bcp14>MAY</bcp14> also add any property providing service information.</t>
      <t>Fields included in the &quot;brief&quot; "brief" and &quot;full&quot; "full" field set responses MUST <bcp14>MUST</bcp14> take into account the user's access and authorization levels.</t>
      <figure anchor="fieldSet-id-response-example" title="Example anchor="fieldSet-id-response-example">
        <name>Example of RDAP response according Response According to the &quot;id&quot; field set">
        <artwork xml:space="preserve"> "id" Field Set</name>
<sourcecode type="json">
{
  "rdapConformance": [
    "rdap_level_0",
    "subsetting"
  ],
  ...
  "domainSearchResults": [
    {
      "objectClassName": "domain",
      "ldhName": "example1.com",
      "links": [
        {
        "value": "https://example.com/rdap/domain/example1.com",
        "rel": "self",
        "href": "https://example.com/rdap/domain/example1.com",
        "type": "application/rdap+json"
        }
      ]
    },
    {
      "objectClassName": "domain",
      "ldhName": "example2.com",
      "links": [
        {
        "value": "https://example.com/rdap/domain/example2.com",
        "rel": "self",
        "href": "https://example.com/rdap/domain/example2.com",
        "type": "application/rdap+json"
        }
      ]
    },
    ...
  ]
}
        </artwork>
</sourcecode>
      </figure>
    </section>
    <section anchor="negative-answers" title="Negative Answers"> anchor="negative-answers">
      <name>Negative Answers</name>
      <t>Each request including an empty or unsupported &quot;fieldSet&quot; "fieldSet" value MUST <bcp14>MUST</bcp14> produce an HTTP 400 (Bad Request) response code.  Optionally, the response MAY <bcp14>MAY</bcp14> include additional information regarding the supported field sets in the HTTP entity body (<xref target="field-set-error"/>).</t>
      <figure anchor="field-set-error" title="Example anchor="field-set-error">
        <name>Example of RDAP error response due Error Response Due to an invalid field set included Invalid Field Set Included in the request">
        <artwork xml:space="preserve"> Request</name>

<sourcecode type="json">
{
    "errorCode": 400,
    "title": "Field set 'unknownfieldset' is not valid",
    "description": [
        "Supported field sets are: 'afieldset', 'anotherfieldset'."
    ]

}
        </artwork>
</sourcecode>
      </figure>
    </section>
    <section anchor="IANA-considerations" title="IANA Considerations"> anchor="IANA-considerations">
      <name>IANA Considerations</name>
      <t>IANA is requested to register has registered the following value in the RDAP Extensions Registry:</t>

<t><list style="none">
      <t>Extension "RDAP Extensions" registry:</t>

<dl spacing="compact">

<dt>Extension identifier: subsetting</t>
      <t>Registry
</dt>
<dd>subsetting
</dd>

<dt>Registry operator: Any</t>
      <t>Published
</dt>
<dd>Any
</dd>

<dt>Published specification: This document.</t>
      <t>Contact: IETF &lt;iesg@ietf.org&gt;</t>
      <t>Intended
</dt>
<dd>RFC 8982
</dd>

<dt>Contact:
</dt>
<dd>IETF &lt;iesg@ietf.org&gt;
</dd>

<dt>Intended usage: This
</dt>
<dd>This extension describes a best practice for partial response provisioning.</t>
</list></t>

   </section>

    <section anchor="impl-status" title="Implementation Status">
      <t>NOTE: Please remove this section and the reference to RFC 7942 prior to publication as an RFC.</t>

      <t>This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in <xref target="RFC7942"/>.  The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs.  Please note that the listing of any individual implementation here does not imply endorsement by the IETF.  Furthermore, no effort has been spent to verify 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.</t>

      <t>According to RFC 7942, "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature.  It is up to the individual working groups to use this information as they see fit".</t>

      <section anchor="iit-cnr-registro-it" title="IIT-CNR/Registro.it">
        <t><list style="none">
	  <t>Responsible Organization: Institute of Informatics and Telematics of the National Research Council (IIT-CNR)/Registro.it</t>
	  <t>Location: https://rdap.pubtest.nic.it/</t>
	  <t>Description: This implementation includes support for RDAP queries using data from .it public test environment.</t>
	  <t>Level of Maturity: This is an "alpha" test implementation.</t>
	  <t>Coverage: This implementation includes all of the features described in this specification.</t>
	  <t>Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it</t>
	</list></t>
      </section>

      <section anchor="apnic" title="APNIC">
        <t><list style="none">
	  <t>Responsible Organization: Asia-Pacific Network Information Centre</t>
	  <t>Location: https://github.com/APNIC-net/rdap-rmp-demo/tree/partial-response</t>
	  <t>Description: A proof-of-concept for RDAP mirroring.</t>
	  <t>Level of Maturity: This is a proof-of-concept implementation.</t>
	  <t>Coverage: This implementation includes all of the features described in this specification.</t>
	  <t>Contact Information: Tom Harrison, tomh@apnic.net</t>
	</list></t>
      </section> provisioning.
</dd>

</dl>

    </section>

    <section anchor="security-considerations" title="Security Considerations"> anchor="security-considerations">
      <name>Security Considerations</name>
      <t>A search query typically requires more server resources (such as memory, CPU cycles, and network bandwidth) when compared to a lookup query.  This increases the risk of server resource exhaustion and subsequent denial of service.  This risk can be mitigated by supporting the return of partial responses combined with other strategies (e.g. (e.g., restricting search functionality, limiting the rate of search requests, and truncating and paging results).</t>
      <t>Support for partial responses gives RDAP operators the ability to implement data access control policies based on the HTTP authentication mechanisms described in <xref target="RFC7481"/>.  RDAP operators can vary the information returned in RDAP responses based on a client's access and authorization levels.  For example:</t>

        <t><list style="symbols">
      <ul>
        <li>
          <t>the list of fields for each set can differ based on the client's access and authorization levels;<vspace blankLines='1' /></t>
	  <t>the levels;</t>
          <t/>
        </li>
        <li>the set of available field sets could be restricted based on the client's access and authorization levels.</t>
	</list></t> levels.</li>
      </ul>
      <t>Servers can also define different result limits according to the available field sets, so a more flexible truncation strategy can be implemented.  The new query parameter presented in this document provides RDAP operators with a way to implement a server that reduces inefficiency risks.</t>
    </section>
  </middle>
  <back>
    <references title="Normative References">
      &RFC2119;
      &RFC5890;
      &RFC7230;
      &RFC7480;
      &RFC7481;
      &RFC7482;
      &RFC7483;
	 &RFC7942;
      &RFC8174;
      &RFC8288;
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5890.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7230.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7480.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7481.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7482.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7483.xml"/>

        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8288.xml"/>
      </references>

    <references title="Informative References">
      <references>
        <name>Informative References</name>

        <reference anchor='CQL' target='https://github.com/gregwhitaker/catnap/wiki/Catnap-Query-Language-Reference'> anchor="CQL" target="https://github.com/gregwhitaker/catnap/wiki/Catnap-Query-Language-Reference">
          <front>
            <title>Catnap Query Language Reference</title>
            <author initials='G.' surname='Whitaker' fullname='Greg Whitaker'> initials="G." surname="Whitaker" fullname="Greg Whitaker">
		</author>
            <date year='2017' month='September' /> year="2017" month="September"/>
          </front>
	  <refcontent>commit d4f402c</refcontent>
        </reference>

        <reference anchor='HATEOAS' target='https://www.e4developer.com/2018/02/16/hateoas-simple-explanation/'> anchor="HATEOAS" target="https://www.e4developer.com/2018/02/16/hateoas-simple-explanation/">
          <front>
            <title>HATEOAS - a simple explanation</title>
            <author initials='B.' surname='Jedrzejewski' fullname='Bartosz Jedrzejewski'> initials="B." surname="Jedrzejewski" fullname="Bartosz Jedrzejewski">
		</author>
            <date year='2018'/> month="February" year="2018"/>
          </front>
        </reference>

        <reference anchor='REST' target='http://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation.pdf'> anchor="REST" target="https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation.pdf">
          <front>
            <title>Architectural Styles and the Design of Network-based Software Architectures</title>
            <author initials='R.' surname='Fielding' fullname='Roy initials="R." surname="Fielding" fullname="Roy Thomas Fielding'>
                <organization>PH.D. DISSERTATION, UNIVERSITY OF CALIFORNIA, IRVINE</organization> Fielding">
            </author>
            <date year='2000'/> year="2000"/>
          </front>
	  <refcontent>Ph.D. Dissertation, University of California, Irvine</refcontent>

        </reference>
      </references>
    </references>
    <section anchor="approaches-to-partial-response-implementation" title="Approaches anchor="approaches-to-partial-response-implementation">
      <name>Approaches to Partial Response Implementation"> Implementation</name>
      <t>Looking at the implementation experiences of partial response responses offered by data providers on the web, two approaches are observed:</t>

        <t><list style="symbols">
      <ul>
        <li>
          <t>the client explicitly describes the data fields to be returned;<vspace blankLines='1' /></t>
	  <t>the returned;</t>
          <t/>
        </li>
        <li>the client describes a name identifying a server-defined set of data fields.</t>
	</list></t> fields.</li>
      </ul>
      <t>The former is more flexible than the latter because clients can specify all the data fields they need.  However, it has some drawbacks:</t>

        <t><list style="symbols">
	  <t>fields
      <ul>
        <li>
          <t>Fields have to be declared according to a given syntax.  This is
          a simple task when the data structure of the object is flat, but it
          is much more difficult when the object has a tree structure like
          that of a JSON object.  The presence of arrays and deep nested
          objects complicate both the syntax definition of the query and,
          consequently, the processing required on the server side;<vspace blankLines='1' /></t>
	  <t>clients side.</t>
          <t/>
        </li>
        <li>
          <t>Clients need to recognize the returned data structure to avoid
          cases when the requested fields are invalid;<vspace blankLines='1' /></t>
	  <t>the invalid.</t>
          <t/>
        </li>
        <li>The request of some fields might not match the client's access and
        authorization levels.  Clients might request unauthorized fields fields, and
        servers have to define a strategy for responding, responding such as always
        returning an error response or returning a response that ignores the
        unauthorized fields.</t>
	</list></t> fields.</li>
      </ul>
      <section anchor="specific-issues-in-rdap" title="Specific anchor="specific-issues-in-rdap">
        <name>Specific Issues Raised by RDAP"> RDAP</name>
        <t>In addition to those listed above, RDAP responses raise some specific issues:</t>

        <t><list style="symbols">
	  <t>relevant
        <ul>
          <li>
            <t>Relevant entity object information is included in a jCard, but
            such information cannot be easily selected because it is split
            into the items of a jagged array;<vspace blankLines='1' /></t>
	  <t>RDAP array.</t>
            <t/>
          </li>
          <li>RDAP responses contain some properties providing service
          information (e.g. (e.g., rdapConformance, links, notices, remarks, etc.) etc.),
          which are not normally selected but they are just as important.
          They could be returned anyway but, in this case, the server would
          provide unrequested data.</t>
	</list></t> data.</li>
        </ul>
        <t>It is possible to address these issues.  For example, the Catnap
        Query Language <xref target="CQL"/> is a comprehensive expression
        language that can be used to customize the JSON response of a RESTful
        web service.  Application of CQL to RDAP responses would explicitly
        identify the output fields that would be acceptable when a few fields
        are requested but it would become very complicated when processing a
        larger number of fields.  In the following, two CQL expressions for a
        domain search query are shown (<xref target="cql-example"/>).  In the
        first, only objectClassName and ldhName are requested.  In the second,
        the fields of a possible WHOIS-like response are listed.</t>
        <figure anchor="cql-example" title="Examples anchor="cql-example">
          <name>Examples of CQL expressions Expressions for a domain search query">
        <artwork xml:space="preserve"><![CDATA[ Domain Search Query</name>

<sourcecode type="http-message"><![CDATA[
https://example.com/rdap/domains?name=example*.com
        &fields=domainSearchResults(objectClassName,ldhName)

https://example.com/rdap/domains?name=example*.com
        &fields=domainSearchResults(objectClassName,ldhName,
                unicodeName,
                status,
                events(eventAction,eventDate),
                entities(objectClassName,handle,roles),
                nameservers(objectClassName,ldhName))
        ]]></artwork>
]]>
</sourcecode>
        </figure>
        <t>The field set approach seems to facilitate RDAP interoperability.
        Servers can define basic field sets which, that, if known to clients, can
        increase the probability of obtaining a valid response.  The usage of
        field sets makes the query string be less complex.  Moreover, the
        definition of pre-defined predefined sets of fields makes it easier to establish
        result limits.</t>
        <t>Finally, considering that there is no real need for RDAP users to
        have the maximum flexibility in defining all the possible sets of
        logically connected fields (e.g. (e.g., users interested in domains usually
        need to know the status, the creation date, and the expiry date of
        each domain), the field set approach is preferred.</t>
      </section>
    </section>
    <section title="Acknowledgements" numbered="no"> numbered="false">
      <name>Acknowledgements</name>
      <t>The authors would like to acknowledge Scott Hollenbeck, Tom Harrison, Karl <contact fullname="Scott Hollenbeck"/>, <contact fullname="Tom Harrison"/>, <contact fullname="Karl Heinz Wolf, Jasdip Singh, Patrick Mevzek, Benjamin Kaduk, Roman Danyliw, Murray Kucherawy, Erik Kline and Robert Wilton Wolf"/>, <contact fullname="Jasdip Singh"/>, <contact fullname="Patrick Mevzek"/>, <contact fullname="Benjamin Kaduk"/>, <contact fullname="Roman Danyliw"/>, <contact fullname="Murray Kucherawy"/>, <contact fullname="Erik Kline"/>, and <contact fullname="Robert Wilton"/> for their contribution to this document.</t>
    </section>

    <section title="Change Log" numbered="no">
      <t>
        <list style="hanging">
          <t hangText="00:">Initial working group version ported from draft-loffredo-regext-rdap-partial-response-03</t>
          <t hangText="01:">Removed &quot;FOR DISCUSSION&quot; items.  Changed the basic field sets from REQUIRED to OPTIONAL.  Removed the definition of fields included in &quot;brief&quot; field set.  Provided a more detailed description of &quot;subsetting_metadata&quot; structure.  Removed some references.</t>
          <t hangText="02:">Added the &quot;Negative Answers&quot; section.  Changed &quot;IANA Considerations&quot; section.</t>
          <t hangText="03:">Added the &quot;unicodeName&quot; field in the id fieldSet when a returned domain or nameserver is an IDN.  Added RFC5890 to &quot;Normative References&quot; section.</t>
          <t hangText="04:">Recommended the RDAP providers to include a &quot;self&quot; link in any field set other than &quot;full&quot;.  Updated &quot;Acknowledgements&quot; section.</t>
          <t hangText="05:">Moved &quot;Approaches to Partial Response Implementation&quot; section to the appendix.</t>
          <t hangText="06:">Clarified the use of self links in &quot;Basic Field Sets&quot; section.  Added APNIC to the implementations of the &quot;Implementation Status&quot; section.</t>
          <t hangText="07:">Changed &quot;only a subset is returned&quot; to &quot;only a subset of fields in each result object is returned&quot; in the &quot;Introduction&quot; section.  Moved the &quot;RDAP Conformance&quot; section up in the document.  Updated the &quot;Acknowledgements&quot; section.</t>
          <t hangText="08:">Changed the rdapConformance tag &quot;subsetting_level_0&quot; to &quot;subsetting&quot;.  Moved <xref target="RFC7942"/> to the &quot;Normative References&quot;.</t>
		  <t hangText="09:">Corrected the &quot;rdapConformance&quot; content in <xref target="fieldSet-id-response-example"/>.</t>
		  <t hangText="10:">Corrected the JSON content in <xref target="subset-link-in-response-example"/>.  Clarified the meaning of both context and target URIs in a result subset link defined in <xref target="subsetting_links"/>.  Updated the &quot;Acknowledgements&quot; section.</t>
            <t hangText="11:">Minor pre-AD review edits.</t>
            <t hangText="12:">Additional minor pre-AD review edits.</t>
            <t hangText="13:">Edits due to Gen-ART review: in the first paragraph of <xref target="rdap-path-segment-specification"/> clarified how field sets are defined by a server, in the first sentence of <xref target="negative-answers"/> replaced SHOULD with MUST.  Other minor edits due to AD review.</t>
            <t hangText="14:">Edits due to IESG review:
              <list style="symbols">
       <t>replaced &quot;fewer data transferred&quot; with &quot;less data transferred&quot; in the &quot;Introduction&quot; section;</t>
       <t>in the &quot;Subsetting Metadata&quot; section:
        <list style="symbols">
          <t>replaced the phrase &quot;collected in a new data structure&quot; with the phrase &quot;collected in a new JSON data structure&quot;;</t>
          <t>replaced &quot;Members are:&quot; with &quot;The AvailableFieldSet object includes the following members:&quot;;</t>
          <t>clarified that an RDAP server MUST define only one default field set;</t>
        </list>
        </t>
       <t>clarified the required members of a Link object in the &quot;Representing Subsetting Links&quot; section;</t>
       <t>rewritten the &quot;Dealing with Relationships&quot; section;</t>
       <t>in the &quot;Basic Field Sets&quot; section:
           <list style="symbols">
           <t>replaced the phrase &quot;include a 'self' link in each field set&quot; with the phrase &quot;include a 'links' field indicating the 'self' link relationship&quot;;</t>
           <t>replaced the phrase &quot;'unicodeName' field MUST be included&quot; with the phrase &quot;'unicodeName' field MUST additionally be included&quot;;</t>
           </list>
       </t>
       <t>in the &quot;Negative Answers&quot; section:
           <list style="symbols">
           <t>replaced the phrase &quot;the response MAY include additional information regarding the negative answer&quot; with the phrase &quot;the response MAY include additional information regarding the supported field sets&quot;;</t>
           <t>added a new example;</t>
           </list>
       </t>
	   <t>replaced the phrase &quot;and subsequent denial of service due to abuse&quot; with the phrase &quot;and subsequent denial of service&quot; in &quot;Security Considerations&quot; section;</t>
       <t>corrected the [REST] reference in the &quot;Informative References&quot; section;</t>
       <t>in &quot;Appendix A&quot;:
        <list style="symbols">
            <t>added the phrase &quot; offered by data providers on the web&quot; after the phrase &quot;Looking at the implementation experiences of partial response&quot;;</t>
            <t>replaced the phrase &quot;servers should define a strategy&quot; with the phrase &quot;servers have to define a strategy&quot;;</t>
            <t>replaced the term &quot;latter approach&quot; with the term &quot;field set approach&quot; in the &quot;Appendix A.1&quot; section;</t>
        </list>
       </t>
       <t>updated the &quot;Acknowledgements&quot; section.</t>
	  </list></t>
            <t hangText="15:">Minor edit in the &quot;Appendix A.1&quot; section;</t>
            <t hangText="16:">Changed a figure containing only an RDAP query into text.  Made the RDAP queries uniform.  Other minor edits.</t>
        </list>
      </t>
    </section>

  </back>
</rfc>