[NOTE: This local archive copy of"XML Activity" was mirrored as a snapshot from the official and canonical URL,http://www.w3.org/XML/Activity, 1999-01-06; please refer to the canonical source document if possible. A few anchors have been placed in this version to facilitate linking to relevant subsections. 1999-01-29.]
Work on XML is being managed as part of W3C'sArchitecture Domain.
Activitystatements provide a managerial overview of W3C's work in thisarea. They are designed to be read from beginning to end, to beinformative and interesting. The role of W3C is given, also thebenefits to the Web community, accomplishments to date and asummary of what the future holds.
For brevity, in this Activity Statement, we often refer to theExtensible Markup Language as simply "XML".
XML -- the Extensible Markup Language -- is asimple, very flexible text format based on SGML (ISO 8879). Designed to meetthe challenges of large-scale electronic publishing, XMLTM will also play an increasinglyimportant role in the exchange of a wide variety of data on theWeb.
XML will
The best way to appreciate what XML looks like is with a simpleexample. Imagine your company sells products on-line. Marketingdescriptions of the products are written in HTML, but names andaddresses of customers, and also prices and discounts are formattedwith XML. Here is the information describing a customer:
<customer-details> <name>Acme Pharmaceuticals Co.</name> <address country="US"> <street>7301 Smokey Boulevard</street> <city>Smallville</city> <state>Indiana</state> <postal>94571</postal> </address> </customer-details>
The XML syntax uses matching start and end tags, such as<name> and </name>, to mark up information. A piece ofinformation marked by the presence of tags is called anelement; elements may be further enriched by attachingname-value pairs (for example, country="US" in the example above)called attributes. Its simple syntax is easy to process bymachine, and has the attraction of remaining understandable tohumans. XML is based on SGML, and is familiar in look and feel tothose accustomed to HTML.
XML is a low-level syntax for representing structured data. Youcan use this simple syntax to support a wide variety ofapplications. This idea is put across in a simplistic way in thediagram below, which shows how XML now underpins a number of Webmark-up languages and applications.
W3C are redeveloping HTML as a suite of XML tag sets so that,although documents will still be marked up using HTML, this willconform to the rules of XML. In this environment mathematicalexpressions can be inserted into documents using MathML, aformatting language written in XML and developed by W3C'sMath working group. Presumably, other domain-specificXML-based tag sets will become candidates for inclusion in HTMLdocuments.
W3C'sMetadata Activity is developingtheResource Description Format (RDF). This uses a simpledata model expressed in XML syntax as the basis for a language forrepresenting properties of Web resources such as images, documentsand the relationships held between them. ThePlatform for Internet Content Selection (PICS), is being recastin RDF. The PICS framework provides a means for attaching labels tomaterial (in particular, to indicate whether it is suitable forchildren).
Finally, theSynchronized MultimediaIntegration Language - (SMIL) is an XML application consistingof a declarative language for scheduling multimedia presentations onthe Web.
Outside of W3C, many groups are already defining new formats forinformation interchange. The number of XML applications appearslikely to grow rapidly. There are many areas, for example, thehealth-care industry, the Inland Revenue, government and finance,where XML applications may be soon be used to store and processdata. XML as a simple method for data representation andorganization will mean that problems of data incompatibility andtedious manual re-keying will, by and large, be solved.
The flexibility of XML makes it ideal for interchange ofstructured data for further processing on the receiving machine.TheW3C Document Object ModelActivity will provide an interoperable set of classes andmethods to manipulate XML documents (as well as HTML documents)from programming languages such as Java, ECMAScript, VBScript, andC++.
XML markup can be used to stucture data to support automaticprocessing. How is software to recognize the markup it exists toprocess, and avoid confusing it with markup designed for the use ofsome other software? For example, one application might use anelement calledaddress to label the mailing address of aperson; in another application,address might instead be usedfor a network address. How would a machine or even a person lookingat the XML markup know which use of "address" is intended in a giveninstance?
What is needed is a method for identifying the conventionsgoverning the use of particular sets of elements. The idea is touse a Web address as a globally unique name for such a set ofconventions. W3C's work onnamespaces is concerned with theelaboration of this idea.
W3C'sXML 1.0 Recommendation wasissued on February 10, 1998. In response to the increasingpopularity of XML as a basis for Web applications, the Activity hasorganized itself into the following groups:
The membership of this group is the chairs of the individualWorking Groups. Its role is to provide a forum for coordinationbetween the Working Groups of the XML Activity, and between the XMLActivity and other parts of W3C, and between the XML Activity andother organizations. In particular, the co-ordination group:
The chair of the XML Coordination Group is Jon Bosak of SunMicrosystems.
While XML 1.0 supplies a mechanism, theDocument TypeDefinition (DTD) for declaring constraints on the use ofmarkup, automated processing of XML documents requires morerigorous and comprehensive facilities in this area. Requirementsare for constraints on how the component parts of an applicationfit together, the document structure, attributes, data-typing, andso on. TheXML Schema Working Group is addressing means fordefining the structure, content and semantics of XML documents.
The co-chairs of the Schema WG are Dave Hollander ofHewlett-Packard and C. M. Sperberg-McQueen, of the University ofIllinois at Chicago and the W3C.
TheXML Linking Working Group is designing hypertextlinks for XML. Engineers defining the way that links are to bewritten in XML have made a distinction for links between objects -"external" links, and "internal" links to locations within XMLdocuments, and both types will receive detailed treatment by thisgroup. The objective of the XML Linking Working Group is to designadvanced, scalable, and maintainable hyperlinking and addressingfunctionality for XML
The working draftsXML LinkingLanguage (XLink) andXML PointerLanguage (XPointer) represent the basis on which the work ofthe Linking WG will proceed.
The chair of the Linking WG is Bill Smith, of SunMicrosystems.
[Note:Mail Archives for comments on XML Linking, viz.,www-xml-linking-comments@w3.org.]
The XML 1.0 Recommendation describes the physical representationof XML documents: the use of brackets, character strings and other"nuts and bolts" which make up the language. TheInformation SetWorking Group is looking at more abstract descriptions of XMLdocuments in terms of document tree structures, elements, theirattribute lists and so on. The idea is to provide a commonreference set that other specifications can use and extend toconstruct their underlying data models, thus helping to ensureinteroperability among the various XML-based specifications andamong XML software tools in general.
The chair of the Information Set WG is David Megginson, invitedexpert.
The XML standard supports logical documents composed of possiblyseveral entities. It may be desirable to view, edit, or interchangeone or more of the entities or parts of entities withoutinterchanging the entire document. The problem, then, is how toprovide to a recipient of such a fragment the appropriateinformation about the context that fragment had in the largerdocument.
The goal of theFragment Working Group is to define a wayto send fragments of an XML document without having to send all orpart of the parent document as well. The delivered fragments caneither be viewed or edited immediately or accumulated for lateruse, assembly, or other processing.
The chair of the XML Fragment WG is Paul Grosso ofArborText.
[Note:Mail archives for the XML Fragments List,www-xml-fragment-comments@w3.org.]
TheXML Syntax Working Group is concerned with severalaspects of XML:
The co-chairs of the XML Syntax WG are Tim Bray, invited expert,and Joel Nava of Adobe.
The Schema Working group plans to deliver Requirements, WorkingDrafts, and Proposed Recommendations on data typing and schemalanguage in 1999.
The Fragment Working Group expects to issue a W3C ProposedRecommendation for Fragment Interchange by Summer 1999
The Syntax Group plans to deliver:
all during the middle of next year (1999).
The Information Set Working Group plans to have completed theFirst public XML Information Set Working Draft to be released bythe end of 1998 and a Proposed Recommendation by Spring 1999.
Dan Connolly, XML ActivityLead
Copyright © 1998W3C (MIT,INRIA,Keio ), All RightsReserved. W3Cliability,trademark,documentuse andsoftware licensing rules apply. Your interactions with thissite are in accordance with ourpublic andMember privacy statements.