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<h1><a name="title" id="title"></a>Framework for SML EPR-Based Reference Schemes</h1>
<h2><a name="w3c-doctype" id="w3c-doctype"></a>W3C Working Group Note 30 June 2009</h2><dl><dt>This version:</dt><dd>
<a href="http://www.w3.org/TR/2009/NOTE-sml-epr-ref-scheme-20090630">
http://www.w3.org/TR/2009/NOTE-sml-epr-ref-scheme-20090630</a></dd>
<dt>Latest version:</dt><dd><a href="http://www.w3.org/TR/sml-epr-ref-scheme">http://www.w3.org/TR/sml-epr-ref-scheme</a></dd>
<dt>Author:</dt><dd>Kirk Wilson, CA, Inc.</dd>
<dt>Editor:</dt><dd>Len Charest, Microsoft Corporation</dd></dl>
<p class="copyright">
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> &copy; 2009 <a href="http://www.w3.org/">
<acronym title="World Wide Web Consortium">W3C</acronym></a><sup>&reg;</sup> (<a href="http://www.csail.mit.edu/">
<acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.org/">
<acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and
<a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.
</p>
</div>
<hr>
<div style="text-align:center;font-style:italic" id="toc-jump"><a href="#toc">[Jump to Table of Contents]</a></div>
<h2 id="abstract">Abstract</h2>
The Service Modeling Language [<cite><a href="#ref-SML">SML</a></cite>]
specification extends the Extensible Mark-up Language [<cite><a href="#ref-XML">XML</a></cite>]
and XML Schema [<cite><a href="#ref-XMLSchema">XML Schema</a></cite>]
with a mechanism for incorporating into XML documents references to other documents or document
fragments. This technical note addresses the construction of SML reference
schemes for document or document fragment references that employ WS-Addressing
[<cite><a href="#ref-WSA">WS-A</a></cite>] endpoint references (EPRs).
<h2 id="status">Status of this Document</h2>
<p><em>This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and
the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p>
<p>This is the <a
href="http://www.w3.org/2005/10/Process-20051014/tr.html#q75">W3C Working Group Note</a> &quot;Framework for SML EPR-based
Reference Schemes&quot;. This document was produced by the <a
href="http://www.w3.org/XML/SML/">SML
Working Group</a> as part of the <a href="http://www.w3.org/XML/Activity">XML Activity</a>.</p>
<p>Please submit comments on this document using the
<a href="http://www.w3.org/XML/SML/#issues">procedure described on the Working Group's home page</a>.
In summary, the Working Group solicits comments in Bugzilla from those who have access,
and on the Working Group's
<a href="mailto:public-sml@w3.org">public mailing list</a>
(<a href="http://lists.w3.org/Archives/Public/public-sml/">public archive</a>)
from others.</p>
<p>Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is a
draft document and may be updated, replaced or obsoleted by other documents at
any time. It is inappropriate to cite this document as other than work in progress.</p>
<p>This document is intended to serve as guidance for designing SML reference schemes that employ
WS-Addressing [<cite><a href="#ref-WSA">WS-A</a></cite>] endpoint references
(EPRs). Currently, this document is consistent with the Service Modeling
Language (SML) 1.1 specification [<a href="#ref-SML">SML</a>] and the Service Modeling
Language Interchange Format (SML-IF) 1.1 specification [<a
href="#ref-SMLIF">SML-IF</a>], but it may be obsoleted
by future versions of these specifications. The SML WG does not expect this document to become a W3C Recommendation.</p>
<p>This document was produced by a group operating under the <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>. W3C maintains a <a
rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/41079/status">public list of any patent disclosures</a> made in connection with
the deliverables of the group; that page also includes instructions for
disclosing a patent. An individual who has actual knowledge of a patent which
the individual believes contains <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the
information in accordance with <a
href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.</p>
<div id="toc">
<h2 id="toc-head">Table of Contents</h2>
<div class="toc-list">
1. <a href="#introduction">Introduction</a><br>
2. <a href="#framework">Framework: Core Characteristics of EPR-Based Reference Schemes</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;2.1. <a href="#frameepr">Framework for SML EPR Reference Schemes</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;2.2. <a href="#exampleepr">Example of an SML EPR Reference Scheme: The University Course Example</a><br>
3. <a href="#usingframe">Using the Framework with Web Services Protocols</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;3.1. <a href="#smlref">An SML Reference Scheme</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;3.2. <a href="#wsrfexample">WS-RF Reference Scheme Example</a><br>
4. <a href="#interchange">Interchange and Interoperability Considerations</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;4.1. <a href="#usingepr">Using EPR-Based SML Reference Schemes in SML-IF Documents</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.1.1. <a href="#aliases">Document Aliases</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.1.2. <a href="#locators">Document Locators</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;4.2. <a href="#interop">Interoperability</a><br>
5. <a href="#summary">Summary</a>
</div>
<h2 id="appendices">Appendices</h2>
<div class="toc-list">
A. <a href="#references">References</a><br>
B. <a href="#acknowl">Acknowledgments</a><br>
</div>
</div>
<hr>
<h2 id="introduction">1. Introduction
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<p>The Service Modeling Language [<cite><a href="#ref-SML">SML</a></cite>] specification extends
the Extensible Mark-up Language [<cite><a href="#ref-XML">XML</a></cite>] and XML Schema
[<cite><a href="#ref-XMLSchema">XML Schema</a></cite>]
with a mechanism for incorporating into XML documents references to other
documents or document fragments. A reference to another document or document
fragment is encoded by means of markup compliant with one or more <a href="http://www.w3.org/TR/2009/REC-sml-20090512/#Reference_Schemes">reference
schemes</a> as defined in SML ([<cite><a href="#ref-SML">SML</a></cite>] , section 4.3). The SML specification defines
one reference scheme, the SML URI Reference Scheme, which enables XML documents
to use URIs [<cite><a href="#ref-RFC3986">RFC 3986</a></cite>] to identify documents or document fragments. The SML URI
Reference Scheme has the significant advantage of <a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#ConformanceClause">guaranteeing referential
conformance</a> of models that are exchanged between vendors ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>],
section 5.1). </p>
<p>However, not all documents or document fragments can be retrieved simply by means of a URI that
may be dereferenced. For example, the targeted document may be accessible only through
a Web service endpoint. There are several protocols, each specifying its own
message exchange pattern (MEP), that make documents and document fragments
available through inter with a Web service. These include (but are not
limited to):</p>
<ul type=disc>
<li>WS-Transfer
[<cite><a href="#ref-WST">WS-T</a></cite>] and WS-Management [<cite><a href="#ref-WSMAN">WS-Man</a></cite>] </li>
<li>WS-ResourceProperties
[<cite><a href="#ref-WSRP">WS-RP</a></cite>] and Web Services Distributed
Management [<cite><a href="#ref-WSDM">WSDM</a></cite>] </li>
<li>CMDB Federation
[<cite><a href="#ref-CMDBf">CMDBf</a></cite>] </li>
</ul>
<p>Other such services may be defined in the future. It is a common characteristic of these
services that their endpoints must be addressed using endpoint references
(EPRs) as defined in the WS-Addressing specification [<cite><a href="#ref-WSA">WS-A</a></cite>]. Consequently, this note
considers how SML reference schemes can use Web services endpoint references to
refer to services that provide documents or document fragments through message
exchanges.</p>
<p>The SML specification provides a mechanism to define other reference schemes beyond the
SML URI Reference Scheme in order to accommodate special purpose reference
schemes as well as reference schemes that fall outside of the capabilities of
URIs. The purpose of this Note is to propose a framework for defining SML
reference schemes that accommodate references to documents accessed via EPRs.</p>
<p>EPRs cannot simply be placed in browsers and dereferenced to locate the target resource.
Processors must know how to process a given EPR and this knowledge often
involves knowing (1) the operations offered by the service and (2) the protocol
required for invoking the targeted operation of the service. In this sense, the
use of EPRs goes beyond the standard architecture of the Web [<cite><a
href="#ref-AWWW">AWWW</a></cite>]. Therefore, use of the
SML URI Reference Scheme is encouraged and remains the recommended approach for
SML models. Nevertheless, it is recognized that in some cases model documents
may be accessible only through a service that requires being addressed by means
of an EPR. For further discussion of EPRs and interoperability, see <a
href="#interop"><b>section 4.2</b></a>.</p>
<h2 id="framework">2. Framework: Core Characteristics of EPR-Based Reference Schemes
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<p>This section proposes a set of characteristics, or framework, for EPR-based SML reference
schemes. These characteristics are based on the <a href="http://www.w3.org/TR/2009/REC-sml-20090512/#Reference_Schemes">Reference Scheme definition
requirements</a> of SML ([<cite><a href="#ref-SML">SML</a></cite>], section 4.3 ).</p>
<h3 id="frameepr">2.1 Framework for SML EPR Reference Schemes</h3>
<p>The following guidance is recommended for defining EPR-based SML reference schemes:</p>
<ol class="enumar">
<li><p>An SML reference element should be identified as an instance of an EPR-based reference scheme if and
only if exactly one element information item whose
<a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[local name]</a> is <code>
EndpointReference</code> and whose
<a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[namespace name]</a> is defined by a WS-Addressing
specification (for example, <a href="http://www.w3.org/2005/08/addressing">
<code>http://www.w3.org/2005/08/addressing</code></a>)
is present as a child of the SML reference element.</p></li>
<li><p>An instance of an EPR-based SML reference scheme should be resolved by the SML validator by
constructing the appropriate message to the service based on the provided EPR
and any additional information it has or is provided about how to interact with
the Web service endpoint. This additional information includes the signature of
the operation that is to be invoked to access the targeted document or document
fragment. This operation needs to be bound into a message to the service (e.g.,
a SOAP message [<cite><a href="#ref-SOAP">SOAP</a></cite>]) according the rules
identified below (items a through c).</p>
<p>Note that to resolve an instance of an EPR-based SML reference
scheme compliant with this framework, the SML validator must be a Web services
client. If the validator does not have adequate information to construct the
appropriate Web services request to the service providing access to the
targeted document, then the EPR-based SML reference is unresolved.</p></li>
<li><p>The resolution process should conform to the following rules:</p>
<ol class="enumla">
<li><p>The Web service client should follow the appropriate binding rules for the EPR as specified in the
WS-Addressing specification.</p></li>
<li><p>The appropriate binding rules for the operation as specified in the Web Service Description Language
(WSDL) [<cite><a href="#ref-WSDL">WSDL</a></cite>] <code>binding</code> element should be applied
in constructing the request to the service.</p></li>
<li><p>The SML <a href="http://www.w3.org/TR/2009/REC-sml-20090512/#target">reference
target</a> (see [<cite><a href="#ref-SML">SML</a></cite>], section 2.2)
should be the content or a child within the content of the service response message.
If there is no response message returned by the service (as defined by the
service protocol), then the SML reference is unresolved.</p></li>
</ol></li>
</ol>
<p>The WS-Addressing specification defines the value of the abstract
<a href="http://www.w3.org/TR/2006/REC-ws-addr-core-20060509#eprinfomodel">[address]</a> property
as an IRI [<cite><a href="#ref-RFC3987">RFC 3987</a></cite>]. Since the IRI in the <code>wsa:Address
</code> element of the EPR identifies only an endpoint of a service and typically requires out-of-band
knowledge to retrieve a document or document fragment from that endpoint, an
EPR-based SML reference scheme usually does not use <a href="http://www.w3.org/TR/2009/REC-sml-20090512/#target_complete_identifier">
target-complete identifiers</a>. This Note should not be interpreted as excluding the possibility that the
design of a Web service could allow target-complete identifiers.</p>
<p>If this Framework is adopted as a normative basis for defining EPR-based SML reference schemes,
then testing compliance with the framework would require the following changes
to the language of the framework.</p>
<ul type=disc>
<li>All positive Framework assertions (e.g. &quot;should&quot;, &quot;is&quot;)
<span class="rfc2119">MUST</span> be interpreted as requirements
(<span class="rfc2119">MUST</span>s) in conformity with RFC 2119
[<cite><a href="#ref-RFC2119">RFC 2119</a></cite>].</li>
<li>All negative Framework assertions (e.g. &quot;should not&quot;, &quot;is
not&quot;) <span class="rfc2119">MUST</span> be interpreted as requirements
(<span class="rfc2119">MUST NOT</span>s) in conformity with RFC 2119.</li>
<li>All Framework assertions of explicit variability (e.g.
&quot;may&quot;) <span class="rfc2119">MUST</span> be interpreted as
<a href="http://www.w3.org/TR/2009/REC-sml-20090512/#implementation_defined">implementation-defined</a>
([<cite><a href="#ref-SML">SML</a></cite>], section 2.2) recommendations (<span class="rfc2119">SHOULD</span>s)
in conformity with RFC 2119.</li>
</ul>
<p>As noted in point 2 above, the additional knowledge that is required by a Web service client to
resolve an instance of the an EPR-based reference scheme may include knowledge
of the operations supported by the service endpoint. Because the operations are
typically not provided in the EPR itself, and the Framework does not constrain
these bindings, two otherwise equal EPRs associated with different service
bindings could target different documents. Specific knowledge regarding the
MEPs needed to interact with the service pointed to by the EPR may need to be
made available to the SML model validator. See <a href="#smlref"><b>section 3.1</b></a> for a means by which such
knowledge may be made available through an EPR-based SML reference scheme.</p>
<h3 id="exampleepr">2.2 Example of an SML EPR Reference Scheme: The University Course Example</h3>
<p>Consider thefollowing simple XML document:</p>
<div class="exampleInner">
<pre>&lt;UniversityCourses xmlns=&quot;http://www.university.example.org/ns&quot;&gt;
&lt;PHY101&gt;
. . .
&lt;/PHY101&gt;
&lt;PHY102&gt;
. . .
&lt;/PHY102&gt;
. . .
&lt;/UniversityCourses&gt;
</pre></div>
<p>This simple document will be used in both the following example and the EPR-based SML
reference scheme to be developed in <a href="#usingframe"><b>section 3</b></a>. In the following example
we will assume that each course entry is indexed by an information item named <code>CourseName</code>, whose type is <code>
xs:ID</code> or <code>xs:keyref</code> and whose value is the name of the element.</p>
<p>The following example illustrates the use of an EPR-based SML reference scheme that is
compliant with the Framework. The <code>EnrolledCourse</code> element references a course named
<code>PHY101</code> from the preceding document:</p>
<div class="exampleInner">
<pre>&lt;EnrolledCourse xmlns:sml=&quot;http://www.w3.org/sml/2007/02&quot;
sml:ref=&quot;true&quot;&gt;
&lt;wsa:EndpointReference xmlns:wsa=&quot;http://www.w3.org/2005/08/addressing&quot;&gt;
&lt;wsa:Address&gt;
http://www.university.example.org?CourseName=PHY101
&lt;/wsa:Address&gt;
&lt;/wsa:EndpointReference&gt;
&lt;/EnrolledCourse&gt;
</pre></div>
<p>The service providing the university's list of courses is addressed by the URI <code>
http://www.university.example.org</code>. The service endpoint
expects a course name to be encoded in the query component of the IRI in the <code>wsa:Address</code> element.
Access to the same content may require a different EPR-based SML reference scheme if the
university's service interface involves a different means to target the desired
fragment. For example, <a href="#wsrfexample"><b>section 3.2</b></a> provides another example
of an SML reference using a totally different EPR-based SML reference scheme.</p>
<h2 id="usingframe">3. Using the Framework with Web Services Protocols
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<p>Because of the virtually unlimited latitude in specifying Web service interfaces for
retrieving documents, EPR-based SML reference schemes may be defined with
mechanisms to address the requirements of specific service protocols. For
example, it may be desirable to include in the reference scheme definition a
specific <code>wsa:Action</code> that the Web service
client is to use in constructing the message to the service, or to provide a
fragment identifier as a separate operation parameter in the form of a QName or
XPath [<cite><a href="#ref-XPath">XPath</a></cite>] expression. In some cases, because
of the service protocol, it may not be feasible to include this additional
information within the <code>wsa:EndpointReference</code> element itself. The
definition of a specific EPR reference scheme should use the Framework as its
basis and may add several conditions for identifying an instance of the
specific scheme.</p>
<h3 id="smlref">3.1 An SML Reference Scheme for the WS-ResourceFramework</h3>
<p>Let us assume that the course listing in the previous example (<a
href="#exampleepr"><b>section 2.2</b></a>) is
maintained by a WS-Resource conformant to the <i>WS-ResourceFramework</i> (WS-RF)
specification [<cite><a href="#ref-WSRF">WS-RF</a></cite>]. The
WS-ResourceFramework requires the use of EPRs to address conformant services.
A definition of a specific SML Reference Scheme based on the
WS-ResourceFramework might proceed as follows:</p>
<h4 id="wsrfdef">SML WS-RF Reference Scheme Definition:</h4>
<ol class="enumar">
<li><p>This reference scheme fully complies with the Framework defined in <a
href="#frameepr"><b>section 2.1</b></a>.</p></li>
<li><p>An SML reference element is identified as an instance of the SML WS-RF Reference
Scheme if and only if it is identified as using the Framework and it contains
the following:</p>
<ol class="enumla">
<li><p>It has exactly one child element information item for which all of the following are true</p>
<ol class="enumlr">
<li><p>Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[local name]</a> is <code>EndpointReference</code>.</p></li>
<li><p>Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[namespace name]</a> is <code>http://www.w3.org/2005/08/addressing</code>.</p></li>
</ol></li>
<li><p>It has exactly one child element information item for which all of the following are true</p>
<ol class="enumlr">
<li><p>Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[local name]</a> is <code>Action</code>.</p></li>
<li><p>
Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[namespace name]</a> is <code>http://www.w3.org/2005/08/addressing</code>.</p></li>
<li><p>The content of this element must be a IRI that represents a valid WS-ResourceProperties [<cite><a href="#ref-WSRP">WS-RP</a></cite>] request operation.</p></li>
</ol></li>
<li><p>It has <i>at most</i> one valid WS-RF message request element for which all the following are true:</p>
<ol class="enumlr">
<li><p>Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[local name]</a> corresponds to a WS-ResourceProperties operation element.</p></li>
<li><p>Its <a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">[namespace name]</a> is <code>http://docs.oasis-open.org/wsrf/rp-2</code>.</p></li>
<li><p>The content of this element, if present, is a single QName or XPath expression.</p>
<p><b>NOTE:</b></p>
<p>The WS-ResourceProperties <code>GetResourcePropertyDocument </code>
operation does not require a message request element. The WS-RP operations <code>
GetResourceProperty</code> and <code>Query ResourceProperties</code> require a single element as the content of the SOAP
<code>Body</code>. However, the <code>GetMultipleResourceProperties </code>operation, which may
retrieve multiple resource properties, would, under conditions of normal usage,
yield an invalid SML reference because of referencing multiple elements.</p>
</li>
</ol></li>
</ol></li>
<li><p>Resolution of this reference scheme should conform with the following rules:</p>
<ol class="enumla">
<li><p>The <code>EndpointReference</code>
element is mapped to SOAP <code>Header</code> element(s) as specified in the WS-Addressing SOAP Binding
specification [<cite><a href="#ref-WSASOAP">WS-A SOAP</a></cite>].</p></li>
<li><p>The <code>Action</code> child element is mapped to a SOAP <code>Header</code>
element with the same QName and content value.</p></li>
<li><p>The WS-RF message request element, if present, is mapped to the SOAP
<code>Body</code> element with the same QName and content value.</p></li>
<li><p>The SML reference target is the content of the service response message. If there
is no response message returned by the service, then the SML reference is
unresolved.</p></li>
</ol></li>
<li><p>As a consequence of conforming to the Framework, and not placing additional
constraints on the resolution process sufficient to make it fully deterministic
in the absence of outside knowledge, this reference scheme does not use
target-complete identifiers.</p></li>
</ol>
<p>This definition is not proposed as a normative definition of a WS-ResourceFramework
reference scheme; however, this lack of normative standing should not be taken
as precluding a similar definition being normatively defined. </p>
<p><a href="#usingepr"><b>Section 4.1</b></a> will
identify further components of this definition that are required to insure that
the reference scheme is interoperable.</p>
<h3 id="wsrfexample">3.2 WS-RF Reference Scheme Example</h3>
<p>This section illustrates the WS-RF Reference Scheme defined in the preceding section. For
simplicity, we will use the same simple XML document introduced in the
University Course Example (<a href="#exampleepr"><b>section 2.2</b></a>). To conform to the
WS-ResourceFramework, we assume that the schema of this document is constructed
in the following manner:</p>
<div class="exampleInner"><pre>
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;xs:schema xmlns:xs=&quot;http://www.w3.org/2001/XMLSchema&quot;
xmlns:tns=&quot;http://www.university.example.org/ns&quot;
targetNamespace=&quot;http://www.university.example.org/ns&quot;&gt;
&nbsp;
&lt;xs:complexType name=&quot;CourseType&quot;&gt;
&lt;xs:sequence&gt;
. . .
&lt;/xs:sequence&gt;
&lt;/xs:complexType&gt;
&nbsp;
&lt;xs:element name=&quot;PHY101&quot; type=&quot;tns:CourseType&quot;/&gt;
&lt;xs:element name=&quot;PHY102&quot; type=&quot;tns:CourseType&quot;/&gt;
. . .
&lt;xs:element name=&quot;UniversityCourses&quot;&gt;
&lt;xs:complexType&gt;
&lt;xs:sequence&gt;
&lt;xs:element ref=&quot;tns:PHY101&quot;/&gt;
&lt;xs:element ref=&quot;tns:PHY102&quot;/&gt;
. . .
&lt;/xs:sequence&gt;
&lt;/xs:complexType&gt;
&lt;/xs:element&gt;
&nbsp;
&lt;/xs:schema&gt;</pre>
</div>
<p>This example is not meant to imply that this is the best way to design the XML document or the
schema for this kind of list; it is meant only as a means to enable both of the
SML reference scheme examples to reference instance documents the same simple
structure.</p>
<p>To retrieve the <code>PHY101</code>
element via the WS-RF Reference Scheme, the WS-ResourceProperties
<code>GetResourceProperty</code> operation may be used.
This operation has a <code>wsa:Action</code> as follows:</p>
<div class="exampleInner"><pre>
&lt;wsa:Action&gt;
http://docs.oasis-open.org/wsrf/rpw-2/GetResourceProperty/GetResourcePropertyRequest
&lt;/wsa:Action&gt;</pre>
</div>
<p>The WS-ResourceProperties message request element specifies the QName of the
targeted document fragment, which must be a Global Element Declaration (GED),
as the content value of the element representing the operation:</p>
<div class="exampleInner"><pre>
&lt;wsrp:GetResourceProperty
xmlns:wsrp=&quot;http://docs.oasis-open.org/wsrf/rp-2&quot;
xmlns:tns=&quot;http://www.university.example.org/ns&quot;&gt;
tns:PHY101
&lt;/wsrp:GetResourceProperty&gt;</pre>
</div>
<p>Thus, a functionally equivalent SML reference to the reference in <a
href="#exampleepr"><b>section 2.2</b></a> (for
an identically structured XML instance document) could be specified with the WS-RF
Reference Scheme as follows:</p>
<div class="exampleInner"><pre>
&lt;EnrolledCourse
xmlns:sml=&quot;http://www.w3.org/sml/2007/02&quot;
xmlns:wsrp=&quot;http://docs.oasis-open.org/wsrf/rp-2&quot;
xmlns:wsa=&quot;http://www.w3.org/2005/08/addressing&quot;
sml:ref=&quot;true&quot;&gt;
&lt;wsa:EndpointReference&gt;
&lt;wsa:Address&gt;http://www.university.example.org&lt;/wsa:Address&gt;
&lt;/wsa:EndpointReference&gt;
&lt;wsa:Action&gt;
http://docs.oasis-open.org/wsrf/rpw-2/GetResourceProperty/GetResourcePropertyRequest
&lt;/wsa:Action&gt;
&lt;wsrp:GetResourceProperty
xmlns:tns=&quot;http://www.university.example.org/ns&quot;&gt;
tns:PHY101
&lt;/wsrp:GetResourceProeprty&gt;
&lt;/EnrolledCourse&gt;</pre>
</div>
<p>WS-RF Reference Scheme instances provide to the SML model validator three essential parts for
constructing the message that is to be sent to the university course service:
the EPR of the service, the <code>wsa:Action</code> that is bound into the
SOAP <code>Header</code>, and the content of the
SOAP <code>Body</code>. Note that knowledge of
how to use the service bindings in constructing a SOAP message, for example,
what component(s) should go into the SOAP <code>Header</code> and which
into the SOAP <code>Body</code>, must be made available to the model consumer. This information
is typically provided by the WSDL binding for the service.</p>
<h2 id="interchange">4. Interchange and Interoperability Considerations
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<h3 id="usingepr">4.1 Using EPR-Based SML Reference Schemes in SML-IF Documents</h3>
<p>Interchanging SML models consisting of documents containing SML references that use EPR-based SML
reference schemes requires special consideration. Interchange is performed by
packaging the documents comprising an SML model into a single document as
described in the SML-IF specification. In order to perform interchange set validation,
the SML-IF validator must first look to validate any SML reference in terms of
what is packaged in the SML-IF document itself. If validation fails from this
perspective, SML-IF validators may choose to pursue the reference outside of
the SML-IF document; however, given the complexity of de-referencing an EPR,
SML-IF validators may be reluctant to do so.</p>
<p>In order to support this internal test of SML reference validity, the SML-IF specification
introduces the notion of a document <a
href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#alias">[alias]</a> ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>],
section 5.3.3). For aliases to be usable in the context of SML-IF, an alias
name (a URI) must be derivable from the reference scheme instance so that the
validator can determine what document in the interchange set the reference
scheme is intending to point to. Thus if an EPR-based SML reference scheme will
be used in the context of SML-IF, the reference scheme definition should
include a method for mapping each EPR to a predictable URI. In particular,
consideration should be given to mapping the EPR's
<a href="http://www.w3.org/TR/2006/REC-ws-addr-core-20060509#eprinfomodel">[address]</a> value (an IRI) to
a URI. (However, to simplify the following discussion, this consideration will
be left as an exercise for implementations of this Note.)</p>
<p>The following considerations pertain to the processing of SML references exposing EPR-based
SML reference schemes in SML-IF documents by means of aliasing:</p>
<h4 id="aliases">4.1.1 Document Aliases</h4>
<p>Unless the EPR-based SML reference scheme is sufficiently constrained to make use of
target-complete identifiers, which is unlikely for EPRs, its <code>wsa:Address</code>
cannot be used as an SML-IF document alias. Nevertheless, the
referenced document may be embedded in the SML-IF document. If maintaining the
fidelity of these links during interchange is necessary, several alternatives
are available, including but not limited to:</p>
<ol class="enumar">
<li><p>For each EPR-based SML reference scheme of an SML reference, the SML-IF producer adds a second
reference scheme instance understood by the receiving SML-IF consumer. This
second reference could use a URI that does not follow the SML-IF
<a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#URI_Processing">rules for
resolving target-complete identifiers</a> ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>], section 5.3.4 .) That
is, the URI would fall into &quot;category 3&quot; discussed in that section.
Note that the identifier value must be generated dynamically from the
information given in the EPR reference scheme instance. Care must be taken to
avoid collisions, since SML-IF allows document aliases to be preserved across
multiple interchanges.</p></li>
<li><p>An EPR-based SML reference scheme definition can specify an algorithm for generating target-complete
identifiers for the purpose of <a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#URI_Processing">
SML-IF URI reference processing</a> as described in
SML-IF ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>], section 5.3.4).</p></li>
</ol>
<p>Using the first case as an example, the SML-IF document producer generates a reference scheme
instance based on information in the given instance of the EPR reference scheme
that is sufficient to uniquely identify the target document or document
fragment within the interchange model. Thus, this scheme specifies a document
alias. For example, the SML reference from the example in <a
href="#wsrfexample"><b>section 3.2</b></a> may
have a generated reference scheme instance with an algorithmically generated
identifier as shown in the following:</p>
<div class="exampleInner"><pre>
&lt;EnrolledCourse
xmlns:sml=&quot;http://www.w3.org/sml/2007/02&quot;
xmlns:wsrp=&quot;http://docs.oasis-open.org/wsrf/rp-2&quot;
xmlns:wsa=&quot;http://www.w3.org/2005/08/addressing&quot;
sml:ref=&quot;true&quot;&gt;
&lt;wsa:EndpointReference&gt;
&lt;wsa:Address&gt;http://www.university.example.org&lt;/wsa:Address&gt;
&lt;/wsa:EndpointReference&gt;
&lt;wsa:Action&gt;
http://docs.oasis-open.org/wsrf/rpw-2/GetResourceProperty/GetResourcePropertyRequest
&lt;/wsa:Action&gt;
&lt;wsrp:GetResourceProperty
xmlns:tns=&quot;http://www.university.example.org/ns&quot;&gt;
tns:PHY101
&lt;/wsrp:GetResourceProperty&gt;
<b>&lt;newScheme:generatedWSRFIdentifier</b>
<b>xmlns:newScheme=&quot;http://www.example.com/myNewScheme_namespace&quot;</b>
<b>xmlns:tns=&quot;http://www.university.example.org/ns&quot;&gt;</b>
<b>http://www.university.example.org?GetResourceProperty=tns:PHY101</b>
<b>&lt;/newScheme:generatedWSRFIdentifier&gt;</b>
&lt;/EnrolledCourse&gt;</pre>
</div>
<p>The generated reference scheme instance is comprised by the <code>newScheme:generatedWSRFIdentifier</code>
element. (It is left as an exercise for the reader to trace through the algorithmic steps by which the
URI <code>//www.university.example.org?GetResourceProperty=tns:PHY101</code>
in the generated instance
can be computed from the preceding EPR Reference Scheme instance. Obviously,
the schema declaration of <code>EnrolledCourse</code> must allow additional
elements.)</p>
<p>This new reference scheme targets the document independently of how the document is made
available through the Web service targeted by the preceding EPR-based Reference
Scheme. The alias for this reference would be:</p>
<div class="exampleInner"><pre>
&lt;alias&gt;
http://www.university.example.org?GetResourceProperty=tns:PHY101
&lt;/alias&gt;</pre>
</div>
<p>Moreover, the process by which the identifier is resolved to the targeted document within the
SML-IF document must be defined in the reference scheme definition similar to
the way the resolution process for <a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#URI_Processing">target-complete URI references</a> is defined in
SML-IF ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>], section 5.3.4). (This resolution algorithm is also
left as an exercise for the reader.)</p>
<div class="note"><p class="prefix"><b>Note:</b></p>
<p>While the SML-IF consumer may recognize the reference scheme
added by the SML-IF producer, we assume that the reference scheme will <i>not</i>
be recognized by the SML model processor; thus the SML model processor will not
attempt to resolve it. Should the SML model processor recognize the reference
scheme (e.g., if the SML URI Reference Scheme is used to contain the document
alias URI) and should the SML model processor attempt to resolve it by normal
processing for that reference scheme, the reference may fail. Implementations
may take steps to prevent this failure.</p>
</div>
<p>If the targeted service exposes only the targeted document, or, more precisely, the <code>wsa:Address</code>
element of the EPR uniquely identifies the
target document within the service, it may be possible to utilize the second
strategy above and generate a target-complete identifier to both identify and
serve as a document alias to the document or document fragment in the SML-IF
document. For example, if the service addressed at the URI <code>http://www.university.example.org</code>
in the University Course
Example exposes only that one document, a target-complete identifier in the
preceding example might be:</p>
<div class="exampleInner"><pre>http://www.university.example.org#smlxpath1(/u:UniversityCourses/u:PHY101)</pre></div>
<p>where <code>UniversityCourses</code> is the root element of the document and the <code>u</code> prefix represents the
<code>http://www.university.example.org/ns</code> namespace. It is not
expected that EPR-based SML reference schemes will typically be able to support
a target-complete identifier.</p>
<h4 id="locators">4.1.2 Document Locators</h4>
<p>EPRs as values of the SML-IF <code>document/locator</code> element are subject to
the same semantic and processing requirements as are EPR-based reference
schemes. EPR document locators should be avoided if wide interoperability is
desired.</p>
<h3 id="interop">4.2 Interoperability</h3>
<p>Because EPR-based SML reference schemes cannot in general be represented by SML URI Reference
schemes, an SML-IF document containing EPR-based reference schemes cannot typically
be <a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#ConformanceClause">
referentially conforming</a> as defined by the SML-IF Specification ([<cite><a href="#ref-SMLIF">SML-IF</a></cite>],
section 5.1). However, the two mechanisms defined in <a
href="#aliases"><b>section 4.1.1</b></a> for
generating aliases within the SML-IF document partially address
interoperability issues at the level of the SML-IF document.
Other considerations related to interoperability exists even if the
reference schemes may be be defined with sufficient rigor to insure
interoperability amongst those who adopt the reference scheme. These other
issues include whether model documents are embedded or included by reference
only in the SML-IF document and whether the SML-IF document is
<a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/#Interoperability">schema-complete</a>
([<cite><a href="#ref-SMLIF">SML-IF</a></cite>], section 4.5 ).</p>
<p>Definitions of EPR-based SML reference schemes should be sufficiently rigorous to support
model interoperability amongst those vendors who agree to use a specific
EPR-based reference scheme.</p>
<h2 id="summary">5. Summary
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<p>The following points summarize the issues that should be considered when defining an
EPR-based SML reference scheme.</p>
<ol class="enumar">
<li><p>Consideration should be given to using the Framework Core described in <a
href="#framework"><b>section 2</b></a> and to adopting it as normative.</p></li>
<li><p>Consideration should be given to the operations and their parameters offered by the service interface
through which the document or document fragment is accessed. The critical issue
in defining an EPR-based SML reference scheme is how much of this special
knowledge should be captured in the EPR-based SML reference scheme itself and
how much might be otherwise made available to the model consumer.</p></li>
<li><p>If the EPR-based SML reference scheme will be used in the context of an SML-IF document, then a
method for supporting SML-IF document aliases should be defined as part of the
reference scheme definition. This note explored several strategies by which
this issue could be addressed. These strategies involve:</p>
<ol class="enumla">
<li><p>Defining an algorithm for generating a reference scheme using a URI identifier with an explicitly stated
resolution process, so that targeted documents can be identified within the
SML-IF document by SML-IF aliasing mechanism, or</p></li>
<li><p>Defining an algorithm for generating a target-complete URI reference scheme so that the alias can be
resolved by the mandated process for resolving SML URI Reference Schemes.</p></li>
</ol></li>
</ol>
<h2 id="references">A. References
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<dl>
<dt class="label"><a name="ref-AWWW">[AWWW]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-webarch-20041215/">Architecture of the World Wide Web,
Volume One</a></cite>, I. Jacobs, N. Walsh, Editors. W3C Recommendation, World Wide Web
Consortium, 15 December 2004. This version of the Architecture of the World
Wide Web, Volume One Recommendation is at http://www.w3.org/TR/2004/REC-webarch-20041215/.
The <a href="http://www.w3.org/TR/webarch/">latest version</a> is available at http://www.w3.org/TR/webarch/.</dd>
<dt class="label"><a name="ref-CMDBf">[CMDBf]</a></dt>
<dd><cite><a href="http://www.dmtf.org/standards/published_documents/DSP0252_1.0.0c.pdf">
CMDB Federation Specification 1.0.0</a></cite>. Johnson, Mark, et. al.
Authors. DMTF DSP1095, Work in progress. The <a
href="http://www.dmtf.org/standards/published_documents/DSP0252_1.0.0c.pdf">current working draft document</a>
is available at http://www.dmtf.org/standards/published_documents/DSP0252_1.0.0c.pdf.</dd>
<dt class="label"><a name="ref-RFC2119">[RFC 2119]</a></dt>
<dd><cite><a href="http://www.ietf.org/rfc/rfc2119.txt">Key words for use in RFCs to Indicate
Requirement Levels</a></cite>. S. Bradner, Author. Internet Engineering Task Force, June 1999. Available
at http://www.ietf.org/rfc/rfc2119.txt. </dd>
<dt class="label"><a name="ref-RFC3986">[RFC 3986] </a></dt>
<dd><cite><a href="http://www.ietf.org/rfc/rfc3986.txt">Uniform Resource Identifier (URI):
Generic Syntax </a></cite>, T. Berners-Lee, R. Fielding, L. Masinter, Authors. Internet
Engineering Task Force, January 2005. Available at
http://www.ietf.org/rfc/rfc3986.txt. </dd>
<dt class="label"><a name="ref-RFC3987">[RFC 3987]</a></dt>
<dd><cite><a href="http://www.ietf.org/rfc/rfc3987.txt">Internationalized Resource Identifiers
(IRIs)</a></cite>, M. Duerst, M. Suignard. RFC, Internet Engineering Task Force, January 2005.
Available at http://www.ietf.org/rfc/rfc3987.txt. </dd>
<dt class="label"><a name="ref-SML">[SML]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2009/REC-sml-20090512/">
Service Modeling Language, Version 1.1</a></cite>, Bhalchandra Pandit,
Valentina Popescu, Virginia Smith, Editors. World Wide Web Consortium, 12
May 2009. This version of the Service Modeling Language specification is
available at http://www.w3.org/TR/2009/REC-sml-20090512/. The <a
href="http://www.w3.org/TR/sml/">latest version of Service Modeling Language, Version 1.1</a>
is available at http://www.w3.org/TR/sml/. </dd>
<dt class="label"><a name="ref-SMLIF">[SML-IF]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2009/REC-sml-if-20090512/">
Service Modeling Language Interchange Format Version 1.1</a></cite>,
Bhalchandra Pandit, Valentina Popescu, Virginia Smith, Editors.
World Wide Web Consortium, 12 May 2009. This version of the Service
Modeling Language Interchange Format specification is available at
http://www.w3.org/TR/2009/REC-sml-if-20090512/. The <a
href="http://www.w3.org/TR/sml-if/">latest
version of the Service Modeling Language Interchange Format Version 1.1</a> specification is
available at http://www.w3.org/TR/sml-if/. </dd>
<dt class="label"><a name="ref-SOAP">[SOAP]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2007/REC-soap12-part1-20070427/">SOAP Version 1.2 Part 1: Messaging
Framework (Second Edition)</a></cite>, Martin Gudgin, Marc Hadley, Noah Mendelsohn, Jean-Jacques
Moreau, Henrik Frystyk Nielsen, Anish Karmarkar, Yves Lafon, Editors. World
Wide Web Consortium, 27 April 2007. This version is
http://www.w3.org/TR/2007/REC-soap12-part1-20070427/. The <a
href="http://www.w3.org/TR/soap12-part1/">latest
version</a> is available at http://www.w3.org/TR/soap12-part1/. </dd>
<dt class="label"><a name="ref-WSA">[WS-A]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2006/REC-ws-addr-core-20060509">
Web Services Addressing 1.0 - Core</a></cite>, Martin Gudgin, Marc
Hadley, Tony Rogers, Editors. World Wide Web Consortium, 9 May 2006. This
version of the WS-Addressing Core specification is
http://www.w3.org/TR/2006/REC-ws-addr-core-20060509. The <a
href="http://www.w3.org/TR/ws-addr-core">latest version of WS-Addressing Core
</a> is available at http://www.w3.org/TR/ws-addr-core. </dd>
<dt class="label"><a name="ref-WSASOAP">[WS-A SOAP]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2006/REC-ws-addr-soap-20060509">
Web Services Addressing 1.0 - SOAP Binding</a></cite>,
Martin Gudgin, Marc Hadley, Tony Rogers, Editors. World Wide Web Consortium, 9
May 2006. This version of the WS-Addressing SOAP Binding specification is
http://www.w3.org/TR/2006/REC-ws-addr-soap-20060509. The <a
href="http://www.w3.org/TR/ws-addr-soap">latest
version of WS-Addressing SOAP Binding</a> is available at http://www.w3.org/TR/ws-addr-soap. </dd>
<dt class="label"><a name="ref-WSMAN">[WS-Man]</a></dt>
<dd><cite><a href="http://www.dmtf.org/standards/published_documents/DSP0226.pdf">
WS-Management Specification, 1.0.0</a></cite>. Raymond McCollum, Bryan
Murray, Brian Reistad, Editors. DMTF DSP0226. This version available at
http://www.dmtf.org/standards/published_documents/DSP0226.pdf. </dd>
<dt class="label"><a name="ref-WSRF">[WS-RF]</a></dt>
<dd><cite><a href="http://www.oasis-open.org/specs/index.php#wsrf">
WS-ResourceFramework</a></cite> is a family of
specifications consisting of WS-Resource, WS-ResourceProperties [<cite><a
href="#ref-WSRP">WS-RP</a></cite>], WS-ResourceLifetime,
WS-ServiceGroup, and WS-BaseFaults. <a
href="http://www.oasis-open.org/specs/index.php#wsrf">Current versions of these specifications</a>
are available at http://www.oasis-open.org/specs/index.php#wsrf. </dd>
<dt class="label"><a name="ref-WSRP">[WS-RP]</a></dt>
<dd><cite><a href="http://docs.oasis-open.org/wsrf/wsrf-ws_resource_properties-1.2-spec-os.pdf">
Web Services Resource Properties 1.2</a></cite>, Steve Graham, Jem
Treadwell, Editors. This <a href="http://docs.oasis-open.org/wsrf/wsrf-ws_resource_properties-1.2-spec-os.pdf">
version</a> is available at http://docs.oasis-open.org/wsrf/wsrf-ws_resource_properties-1.2-spec-os.pdf.</dd>
<dt class="label"><a name="ref-WST">[WS-T]</a></dt>
<dd><cite><a href="http://www.w3.org/Submission/2006/SUBM-WS-Transfer-20060927/">
Web Services Transfer</a></cite>, J. Alexander et al.
Authors. September 2006. W3C Member Submission. Current <a
href="http://www.w3.org/Submission/2006/SUBM-WS-Transfer-20060927/">version</a> is available at
http://www.w3.org/Submission/2006/SUBM-WS-Transfer-20060927/. </dd>
<dt class="label"><a name="ref-WSDL">[WSDL]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2007/REC-wsdl20-20070626">
Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language</a>,
</cite>R. Chinnici, J. J. Moreau, A. Ryman, S.
Weerawarana, Editors. World Wide Web Consortium, 26 June 2007. This version of
the WSDL 2.0 specification is http://www.w3.org/TR/2006/REC-wsdl20-20070626.
The <a href="http://www.w3.org/TR/wsdl20">latest version of WSDL 2.0</a>
is available at http://www.w3.org/TR/wsdl20. </dd>
<dt class="label"><a name="ref-WSDM">[WSDM]</a></dt>
<dd><cite><a href="http://docs.oasis-open.org/wsdm/wsdm-muws1-1.1-spec-os-01.pdf">
Web Services Distributed Management:
Management using Web Services (MUWS 1.1) Part 1</a></cite>, Vaughn Bullard, William
Vambenepe, Editors. Current <a
href="http://docs.oasis-open.org/wsdm/wsdm-muws1-1.1-spec-os-01.pdf">version</a>
is avaliable at http://docs.oasis-open.org/wsdm/wsdm-muws1-1.1-spec-os-01.pdf.</dd>
<dt class="label"><a name="ref-XML">[XML]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2006/REC-xml-20060816/">
Extensible Markup Language (XML) 1.0
(Fourth Edition)</a></cite>, T. Bray, J. Paoli, C. M. Sperberg-McQueen, and E. Maler,
Editors. World Wide Web Consortium, 10 February 1998, revised 16 August 2006. This edition of
the XML 1.0 Recommendation (http://www.w3.org/TR/2006/REC-xml-20060816)
was the one current at the time the SML specification [<cite><a href="#ref-SML">SML</a></cite>] went to Candidate
Recommendation. Implementations may follow the edition cited or any later edition(s);
it is implementation-defined which edition(s) are supported by the
implementation. The <a href="http://www.w3.org/TR/REC-xml/"> version of XML 1.0</a>
is available at http://www.w3.org/TR/REC-xml.</dd>
<dt class="label"><a name="ref-XMLInfoset">[XML InfoSet]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-xml-infoset-20040204/">XML Information Set
(Second Edition)</a></cite>, John Cowan, Richard Tobin, Editors. World Wide Web Consortium, 4
February 2004. This version of the XML Information Set Recommendation is
http://www.w3.org/TR/2004/REC-xml-infoset-20040204/. The <a
href="http://www.w3.org/TR/xml-infoset/">latest version of XML Information Set</a>
is available at http://www.w3.org/TR/xml-infoset/. </dd>
<dt class="label"><a name="ref-XMLSchema">[XML Schema]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/">XML Schema Part 1: Structures Second
Edition</a></cite>, H. Thompson, D. Beech, M. Maloney, and N. Mendelsohn, Editors. World Wide Web
Consortium, 2 May 2001, revised 28 October 2004. This version of the XML Schema
Part 1 Recommendation is http://www.w3.org/TR/2004/REC-xmlschema-1-20041028.
The <a href="http://www.w3.org/TR/xmlschema-1/">latest version of XML Schema 1.0 Part 1</a> is available at
http://www.w3.org/TR/xmlschema-1. </dd>
<dd><cite><a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">XML Schema Part 2: Datatypes Second
Edition</a></cite>, P. Byron and A. Malhotra, Editors. World Wide Web Consortium, 2 May 2001,
revised 28 October 2004. This version of the XML Schema Part 2 Recommendation
is http://www.w3.org/TR/2004/REC-xmlschema-2-20041028. The <a
href="http://www.w3.org/TR/xmlschema-2/">latest version of XML Schema 1.0 Part 2</a>
is available at http://www.w3.org/TR/xmlschema-2. </dd>
<dt class="label"><a name="ref-XPath">[XPath]</a></dt>
<dd><cite><a href="http://www.w3.org/TR/1999/REC-xpath-19991116">XML Path Language (XPath) Version
1.0</a></cite>, J. Clark and S. DeRose, Editors. World Wide Web Consortium, 16 November 1999.
This version of XML Path Language (XPath) Version 1.0 is
http://www.w3.org/TR/1999/REC-xpath-19991116. The <a
href="http://www.w3.org/TR/xpath">latest version of XML Path Language (XPath) Version 1.0</a>
is available at <a href="http://www.w3.org/TR/xpath">http://www.w3.org/TR/xpath</a>.</dd>
</dl>
<h2 id="acknowl">B. Acknowledgments
<a class="toc-link" href="#toc">[Back to Contents]</a></h2>
<p>The author thanks the members of the SML Working Group, particularly John Arwe (IBM)
and Len Charest, for providing input for this note, and Len Charest for a superb job of editing the
final version.</p>
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