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    additional information that describe how the statements in a Resource Description 
    Framework (RDF) should be interpreted. </p>
  <p>For more information on the RDF Schema recommendation, see <a href="http://www.w3.org/TR/PR-rdf-schema/">http://www.w3.org/TR/PR-rdf-schema</a>.</p>
</blockquote>
<h3><a name="WD"></a>W3C Working Drafts</h3>
A W3C working draft is a reasonable first cut at what the standard will eventually 
be. It makes sense conceptually, and is ready for people to begin implementation. 
The feedback that is developed from the efforts to actually put the standard into 
practice is likely to cause some change to the internal details, but not to the 
overall outline of the specification. 
<blockquote> 
  <h4><a name="XSL"></a>XSL<br>
    Extensible Stylesheet Language</h4>
  <p>The XML standard specifies how to identify data, not how to display it. HTML, 
    on the other hand, told how things should be displayed without identifying 
    what they were. The coalescing XSL standard is essentially a translation mechanism 
    that lets you specify what to convert an XML tag into so that it can be displayed 
    -- for example, in HTML. Different XSL formats can then be used to display 
    the same data in different ways, for different uses. </p>
  <p>The translation part of XSL is pretty complete, and a number of implementations 
    exist. The second part of XSL is a bit more tenuous, however. That part covers 
    <i>formatting objects</i>, also known as <i>flow objects</i>, which give you 
    the ability to define multiple areas on a page and then link them together. 
    When a text stream is directed at the collection, it fills the first area 
    and then &quot;flows&quot; into the second when the first area is filled. 
    Such objects are used by newsletters, catalogs, and periodical publications.</p>
  <p>The latest W3C work on XSL is at <a href="http://www.w3.org/TR/WD-xsl"><code>http://www.w3.org/TR/WD-xsl</code></a>.</p>
  <h4><a name="XLL"></a>XLL<br>
    XML Link Language</h4>
  <p>The XLL protocol consists of two proposed specifications to handle links 
    between XML documents: XLink and XPointer, discussed next. These specifications 
    are still in their preliminary stages, but are sure to have a big impact on 
    how XML documents are used. </p>
  <p></p>
  <blockquote> 
    <p><a name="XLink"></a><b>XLink: </b>The XLink protocol is a proposed specification 
      to handle links between XML documents. This specification allows for some 
      pretty sophisticated linking, including two-way links, links to multiple 
      documents, &quot;expanding&quot; links that insert the linked information 
      into your document rather than replacing your document with a new page, 
      links between two documents that are created in a third, independent document, 
      and indirect links (so you can point to an &quot;address book&quot; rather 
      than directly to the target document -- updating the address book then automatically 
      changes any links that use it). For more information on the XLink specification, 
      see <a href="http://www.w3.org/TR/WD-xml-link"><code>http://www.w3.org/TR/WD-xml-link</code></a>. 
    </p>
    <p><a name="XPointer"></a><b>XPointer:</b> In general, the XLink specification 
      targets a document or document-segment using its ID. The XPointer specification 
      defines mechanisms for &quot;addressing into the internal structures of 
      XML documents&quot;, without requiring the author of the document to have 
      defined an ID for that segment. To quote the spec, it provides for &quot;reference 
      to elements, character strings, and other parts of XML documents, whether 
      or not they bear an explicit ID attribute&quot;. For the latest XPointer 
      specification, see <a href="http://www.w3.org/TR/WD-xptr"><code>http://www.w3.org/TR/WD-xptr</code></a>.</p>
    <h4></h4>
  </blockquote>
  <h5></h5>
  <h4><a name="XHTML"></a>XHTML</h4>
  <p>The XHTML specification is a way of making XML documents that look and act 
    like HTML documents. Since an XML document can contain any tags you care to 
    define, why not define a set of tags that look like HTML? That's the thinking 
    behind the XHTML specification, at any rate. The result of this specification 
    is a document that can be displayed in browsers and also treated as XML data. 
    The data may not be quite as identifiable as &quot;pure&quot; XML, but it 
    will be a heck of a lot easier to manipulate than standard HTML, because XML 
    specifies a good deal more regularity and consistency. </p>
  <p>For example, every tag in a well-formed XML document must either have an 
    end-tag associated with it or it must end in <code>/&gt;</code>. So you might 
    see <code>&lt;p&gt;...&lt;/p&gt;</code>, or you might see <code>&lt;p/&gt;</code>, 
    but you will never see <code>&lt;p&gt;</code> standing by itself. The upshot 
    of that requirement is that you never have to program for the weird kinds 
    of cases you see in HTML where, for example, a <code>&lt;dt&gt;</code> tag 
    might be terminated by <code>&lt;/dt&gt;</code>, by another <code>&lt;dt&gt;</code>, 
    by <code>&lt;dd&gt;</code>, or by <code>&lt;/dl&gt;</code>. That makes it 
    a lot easier to write code!</p>
  <p>The XHTML specification is a reformulation of HTML 4.0 into XML. The latest 
    information is at<br>
    <a href="http://www.w3.org/TR/WD-html-in-xml/"><code>http://www.w3.org/TR/WD-html-in-xml/</code></a>.</p>
  <h4><a name="XMLSchema"></a>XML Schema </h4>
  This specification is built on the schema proposals described below. It defines 
  the types of elements a document can contain, their relationships, and the data 
  they can contain in ways that go far beyond what the current <a href="../glossary.html#DTD">DTD</a> 
  specification provides. See the &quot;Schema Proposals&quot; section below for 
  more insight into the limitations of DTDs. For more information on the XML Schema 
  proposal, see the W3C specs <a href="http://www.w3.org/TR/xmlschema-1/">XML 
  Schema (Structures)</a> and <a href="http://www.w3.org/TR/xmlschema-2/">XML 
  Schema (Datatypes)</a>.</blockquote>
<h5></h5>
<h3><a name="NOTE"></a>W3C &quot;Notes&quot;</h3>
<p>&quot;Notes&quot; are not W3C standards at all. Instead, they are proposals 
  made by various individuals and groups that cover topics that are under consideration. 
  The W3C publishes them so that people who are busy working on the standards 
  and reviewing them have some ideas to get started. One &quot;note&quot; is no 
  more likely to reflect the eventual standard than any other -- each will be 
  judged on its merits and, hopefully, the best features of all will be combined 
  in the W3C draft. Most of the schema proposals to date [Mar 1999] fall into 
  this category.</p>
<h4><a name="schema"></a>Schema Proposals</h4>
<p>Although DTDs let you validate XML documents, they suffer from a number of 
  shortcomings. Many of the issues stem from the fact that a DTD specification 
  is not hierarchical. For a mailing address that contained several &quot;parsed 
  character data&quot; (PCDATA) elements, for example, the DTD might look something 
  like this:</p>
<pre>    &lt;!ELEMENT mailAddress (<b>name</b>, address, zipcode)&gt;
    &lt;!ELEMENT <b>name</b> (#PCDATA)&gt;
    &lt;!ELEMENT address (#PCDATA)&gt;
    &lt;!ELEMENT zipcode (#PCDATA)&gt;
</pre>
<p> As you can see, the specifications are linear. There is no sense of containment, 
  which can pollute the namespace, forcing you to come up with new names for similar 
  elements in different settings. So if you wanted to add another &quot;name&quot; 
  element to the DTD that contained of the elements <code>firstName</code>, <code>middleInitial</code>, 
  and <code>lastName</code>, then you would have to come up with another identifier. 
  You could not simply call it &quot;name&quot; without conflicting with the <code>name</code> 
  element defined for use in a <code>mailAddress</code>. </p>
<p>Another problem with the nonhierarchical nature of DTD specifications is that 
  it is not clear what comments are meant to explain. A comment at the top like 
  <code>&lt;!-- Address used for mailing via the postal system --&gt;</code> would 
  apply to all of the elements that constitute a mailing address. But a comment 
  like <code>&lt;!-- Addressee --&gt;</code> would apply to the <code>name</code> 
  element only. On the other hand, a comment like <code>&lt;!-- A 5-digit string 
  --&gt;</code> would apply specifically to the <code>#PCDATA</code> part of the 
  <code>zipcode</code> element, to describe the valid formats. Finally, DTDs do 
  not allow you to formally specify field-validation criteria, such as the 5-digit 
  (or 5 and 4) limitation for the <code>zipcode</code> field.</p>
<p>To remedy these shortcomings, a number of proposals have been made for a more 
  database-like, hierarchical &quot;schema&quot; that specifies validation criteria. 
  Some of the major proposals are shown below.</p>
<blockquote> 
  <h4></h4>
  <h4><a name="DDML"></a>DDML / Xschema<br>
    Document Definition Markup Language / XSchema<br>
  </h4>
  <p>Document definitions like DTD are good to have, but a DTD has a somewhat 
    strange syntax. DDML is the new name for the older XSchema proposal, which 
    specifies validity constraints for an XML document using XML. DDML is one 
    of several proposals that aim to be the successor to DTD. It is not yet clear 
    what the final validation standard will be.</p>
  <p>For more information on DDML, see <a href="http://www.w3.org/TR/NOTE-ddml"><code>http://www.w3.org/TR/NOTE-ddml</code></a>.</p>
  <h5></h5>
  <h4><a name="DCD"></a>DCD<br>
    Document Content Description<br>
  </h4>
  <p>The DCD proposal is a mechanism for defining a standard XML front end for 
    databases. </p>
  <p>For more information on DCD, see <a href="http://www.w3.org/TR/NOTE-dcd"><code>http://www.w3.org/TR/NOTE-dcd</code></a>.</p>
  <h5></h5>
  <h5></h5>
  <h4><a name="SOX"></a>SOX<br>
    Schema for Object-oriented XML<br>
  </h4>
  <p>SOX is a schema proposal that includes extensible data types, namespaces, 
    and embedded documentation.</p>
  <p>For more information on SOX, see <a href="http://www.w3.org/TR/NOTE-SOX/"><code>http://www.w3.org/TR/NOTE-SOX</code></a>.</p>
</blockquote>
<h4><a name="other"></a>Other W3C Notes</h4>
Other proposals for XML-based standards include: 
<blockquote> 
  <h5></h5>
  <h5></h5>
  <h4><a name="ICE"></a>ICE<br>
    Information and Content Exchange<br>
  </h4>
  <p>ICE is a protocol for use by content syndicators and their subscribers. It 
    focuses on &quot;automating content exchange and reuse, both in traditional 
    publishing contexts and in business-to-business relationships&quot;. </p>
  <p>For more information on ICE, see <a href="http://www.w3.org/TR/NOTE-ice"><code>http://www.w3.org/TR/NOTE-ice</code></a>.</p>
</blockquote>
<h4></h4>
<h3><a name="builders"></a>Standards That Build on XML</h3>
<p>The following standards and proposals build on XML. Since XML is basically 
  a language-definition tool, these specifications use it to define standardized 
  languages for specialized purposes.</p>
<h4>Extended Document Standards</h4>
<blockquote> 
  <h4><a name="SMIL"></a>SMIL<br>
    Synchronized Multimedia Integration Language<br>
  </h4>
  <p>SMIL is a W3C recommendation that covers audio, video, and animations. It 
    also addresses the difficult issue of synchronizing the playback of such elements. 
  </p>
  <p>For more information on SMIL, see <a href="http://www.w3.org/TR/REC-smil/"><code>http://www.w3.org/TR/REC-smil</code></a>.</p>
  <h4><a name="MathML"></a>MathML<br>
    Mathematical Markup Language<br>
  </h4>
  <p>MathML is a W3C recommendation that deals with the representation of mathematical 
    formulas. </p>
  <p>For more information on MathML, see <a href="http://www.w3.org/TR/REC-MathML/"><code>http://www.w3.org/TR/REC-MathML</code></a>.</p>
  <h4><a name="SVG"></a>SVG<br>
    Scalable Vector Graphics<br>
  </h4>
  <p>SVG is a W3C working draft that covers the representation of vector graphic 
    images. (Vector graphic images that are built from commands that say things 
    like &quot;draw a line (square, circle) from point x,y to point m,n&quot; 
    rather than encoding the image as a series of bits. Such images are more easily 
    scalable, although they typically require more processing time to render.)</p>
  <p>For more information on SVG, see <a href="http://www.w3.org/TR/WD-SVG"><code>http://www.w3.org/TR/WD-SVG</code></a>.</p>
  <h4><a name="DrawML"></a>DrawML<br>
    Drawing Meta Language<br>
  </h4>
  <p>DrawML is a W3C note that covers 2D images for technical illustrations. It 
    also addresses the problem of updating and refining such images.</p>
  <p>For more information on DrawML, see <a href="http://www.w3.org/TR/1998/NOTE-drawml-19981203"><code>http://www.w3.org/TR/1998/NOTE-drawml-19981203</code></a>.</p>
</blockquote>
<h4><a name="eComm"></a>eCommerce Standards</h4>
<blockquote> 
  <h4><a name="cXML"></a>cXML<br>
    Commerce XML<br>
  </h4>
  <p>cXML is a RosettaNet (<a href="http://www.rosettanet.org"><code>www.rosettanet.org</code></a>) 
    standard for setting up interactive online catalogs for different buyers, 
    where the pricing and product offerings are company specific. Includes mechanisms 
    to handle purchase orders, change orders, status updates, and shipping notifications.</p>
  <p>For more information on cXML, see <a href="http://corp.ariba.com/News/AribaArchive/cxml.htm"><code>http://corp.ariba.com/News/AribaArchive/cxml.htm</code></a>.</p>
  <h4><a name="CBL"></a>CBL<br>
    Common Business Library<br>
  </h4>
  <p>CBL is a library of element and attribute definitions maintained by CommerceNet 
    (<a href="http://www.commerce.net/"><code>www.commerce.net</code></a>). </p>
  <p>For more information on CBL and a variety of other initiatives that work 
    together to enable eCommerce applications, see <a href="http://www.commerce.net/projects/currentprojects/eco/wg/eCo_Framework_Specifications.html"><code>http://www.commerce.net/projects/currentprojects/eco/wg/eCo_Framework_Specifications.html</code></a>.</p>
</blockquote>
<h4><a name="admin"></a>Software Administration and Maintenance Standards</h4>
<blockquote>
  <h4><a name="DMTF"></a>DMTF <br>
    Distributed Management Task Force</h4>
  <p> The DMTF is a group that is coming up with standards to remotely administer 
    desktop equipment. They are planning to use XML to maintain catalogs of devices 
    and their descriptions, and for other remote-management tasks. This group 
    is not part of the W3C, but their activities appear to have progressed to 
    the draft stage, so they are listed here.</p>
  <p>For more information on this organization, see <a href="http://www.dmtf.org/"><code>http://www.dmtf.org/</code></a>.</p>
  <h4><a name="WebDAV"></a>WebDAV <br>
    Web Distributed Authoring and Versioning</h4>
  <p> WebDAV is an effort from the IETF that uses XML to maintain web servers. 
    It allows a server's content to be created, modified, and changed over an 
    HTTP connection. (The IETF is not affiliated with the W3C, but their &quot;draft 
    standard&quot; is approximately the equivalent of a W3C &quot;recommendation&quot;, 
    so it is included here.)</p>
  <p>For more information, see the "webdav" working group at <a href="http://www.ietf.org"><code>http://www.ietf.org</code></a>.</p>
  <hr size=4>
</blockquote>
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