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Updated: November 4, 1998
(Please check the XML Technical FAQ for additional information in Q&A format.)
Download this document in Microsoft Word (.DOC) format (zipped, 15K) .
XML, the language
What is XML?
Does XML replace HTML?
What are the benefits of adding XML to HTML?
How does XML fit into the Microsoft Windows® Distributed interNet Applications (Windows DNA) strategy for building three-tier, Web-enabled applications?
Where will XML be used on the Web?
Does Microsoft Internet Explorer 4.0 support XML?
What is the level of XML support in Internet Explorer 5 Beta?
What is the difference between SGML and XML?
How are HTML, Dynamic HTML, and XML related?
Will it be necessary to compress XML for transmission over the Web?
How will XML be generated from existing databases?
What is a DTD? What is it used for?
Do Web developers have to include a DTD when they use XML to describe data?
What are XML schemas? How are they different from DTDs?
What are namespaces? Why are they important?
Extensible Stylesheet Language (XSL)
What is XSL? What can you do with XSL today?
XML-Data
Standards
What is the relationship between XML and the World Wide Web Consortium?
What is the status of XML with the W3C?
What is the status of DOM with the W3C?
Where does XSL stand in the W3C?
XML vocabularies and data formats
What are XML vocabularies?
What is CDF?
What is OSD?
What is OFX?
What is RDF?
Tool support
What tools support XML today?
Where will the tools come from in the future?
Extensible Markup Language (XML) is the universal language for data on the Web. It gives developers the power to deliver structured data from a wide variety of applications to the desktop for local computation and presentation. XML allows the creation of unique data formats for specific applications. It is also an ideal format for server-to-server transfer of structured data.
Microsoft expects many authors and developers to use XML and HTML in tandem, for example by using XSL to generate HTML.
There are many benefits to using XML on the Web:
XML is quickly becoming the vehicle for delivering structured data from the middle tier to the desktop. XML-based data can be integrated from multiple back-end (database) sources, using agents on the middle tier. Schemas (see the XML-Data section) can improve this process, as developers can describe and exchange data more precisely.
Because XML describes data in a consistent, self-describing, open format, XML could potentially be used anywhere there is a need for data interchange and delivery. Microsoft expects that initially XML will be used to describe information about HTML pages, as is the case today with the channel definition format (CDF) for building Active Channel™ content, as well as future applications such as searching and distributed printing.
More important, because XML can describe data itself, it will be useful for delivering any kind of data -- such as financial transactions, news updates, weather information, patient records, and legal libraries -- to the desktop. Once on the desktop, applications can compute with the data and dynamically present the data.
Yes, Internet Explorer 4.0 supports XML. It supports the following features:
.
Internet Explorer 5 Beta has the following XML support:
The Standard Generalized Markup Language, or SGML (ISO 8879), is the international standard for defining descriptions of structure and content in electronic documents. XML is a simplified version of SGML; XML was designed to maintain the most useful parts of SGML. While SGML requires that structured documents reference a document type definition (DTD) to be valid, XML allows for "well-formed" data and can be delivered without a DTD. XML was designed so that SGML can be delivered -- as XML -- over the Web.
HTML is used in conjunction with CSS to format and present hyperlinked pages. Dynamic HTML, through the Document Object Model, makes all elements in HTML accessible through language-independent scripting and other programming languages, thus dramatically increasing client-side interactivity without additional requests to the server. The page's object model allows any aspect of its content (including additions, deletions, and movement) to be changed dynamically.
By adding XML for structured data, developers have the technologies they need to build the next generation of rich, flexible Web applications. With XML, they can deliver structured data to the desktop and compute on the data via the XML Object Model. Today developers can display XML-based data in a browser, such as Microsoft Internet Explorer 4.0 and Microsoft Internet Explorer 5 Beta, or in other applications through scripting. In addition, they can also apply formatting rules to the data without complex scripting using XSL stylesheets, which essentially transform the XML-based data into display. These two methods of displaying XML-based data make it possible to generate multiple views of complex data.
In general, the need to compress XML data will be application-dependent and largely a function of the amount of data being moved between the server and the client. XML compresses extremely well because of the repetitive nature of the tags used to describe the structure of the data. Benchmarks will be provided in the future to assist with determining whether compression is necessary. It is worth noting that compression is standard to HTTP 1.1 servers and clients, and XML will automatically benefit from this.
In general, this will be handled using a three-tier architecture. Agents will be built to run on the middle tier to access multiple existing DBMSs and output XML. XML enables the generation of common logical views on these databases, and these agents will also support the ability to generate XML "updategrams" bidirectionally, to inform the client of changes made to the data on the middle tier or database server, and vice versa. Consequently, the agents will be able to receive updategrams from the client and send updates to the DBMS.
The document type definition (DTD) defines the valid syntax of a class of XML documents. That is, it lists a number of element names, which elements can appear in combination with which other ones, what attributes are available for each element type, etc. A DTD uses a different syntax from that used by XML documents.
No. XML can be used to describe data with or without a DTD. The term "valid" XML refers to XML data that references a DTD, while "well-formed" XML refers to XML that does not use a DTD. The addition of well-formed XML is one of the fundamental differences between XML and SGML. Clearly, in both cases, the XML itself must conform to the standards for the language (so, for example, all tags must be closed and tags may not overlap).
[From the W3C XML Activity Page at http://www.w3.org/XML/Activity.html ]
While XML 1.0 supplies a mechanism, the Document Type Definition (DTD), for declaring constraints on the use of markup, automated processing of XML documents requires more rigorous and comprehensive facilities in this area. Requirements are for constraints on how the component parts of an application fit togther, the document structure, attributes, datatyping, and so on. The W3C XML Schema Working Group is addressing means for defining the structure, content and semantics of XML documents.
In Internet Explorer 5 Beta, Microsoft is providing a release of XML Schema as a technology preview that may be useful for developers interested in building prototypes and gaining experience with schema.
This technology preview is based on the XML-Data note submitted to the W3C. XML Schema, as implemented in this technology preview, can be thought of as the subset of the XML-Data submission that corresponds to the feature set proposed for Document Content Description (DCD) .
Microsoft is actively involved in defining the emerging W3C XML schema standard and will track this effort. Developers should note that the version of XML Schema released with Internet Explorer 5 Beta is subject to change.
The namespace facility is another advanced feature of XML, outlined in a W3C working draft. Namespaces allow developers to qualify uniquely the element names and relationships and make these names recognizable to avoid name collisions on elements that have the same name but are defined in different vocabularies. They allow tags from multiple name spaces to be mixed, which is essential if data is coming from multiple sources.
For example, a bookstore may define the <TITLE> tag to mean the title of a book, contained only within the <BOOK> element. A directory of people, however, might define <TITLE> to indicate a person's position, for instance: <TITLE>President</TITLE>. Namespaces help define this distinction clearly.
. Microsoft is tracking the W3C working draft and will be updating this
implementation to match the final W3C recommendation.
XSL is defined as an XML grammar that consists of a set of XSL elements. This grammar can be used to transform XML documents into HTML or XML documents.
You can use XSL for direct browsing of XML files and from the XML DOM. The XML DOM transformNode method supports the use of XSL Elements to perform transformations. The DOM selectNodes and selectSingleNode methods support the XSL pattern-matching syntax that enables sophisticated queries for nodes within a particular context of the overall tree structure.
XML-Data, a specification that has been submitted to the W3C for review, makes XML even more powerful and extensible. It outlines a richer method of describing and validating data, making XML even more powerful for integrating data from multiple disparate sources and building three-tier Web applications.
In January 1998, the W3C acknowledged the Extensible Markup Language XML-Data submission from Microsoft, ArborText Inc., DataChannel Inc., and Inso Corp. The specification is available for public review at http://www.w3.org/TR/1998/NOTE-XML-data-0105/ or http://www.microsoft.com/standards/XML/.
The W3C has an active XML Working Group. Microsoft was one of the co-founders of this group in June 1996, and since then numerous industry players have joined, including Netscape Communications Corp, IBM and Oracle. For more information on the XML standards process, see http://www.w3.org/ .
XML version 1.0 recently moved from the proposed recommendation phase to the recommendation phase, which is the last step in the approval process at the W3C, and is a very stable standard. For more information on the current XML specification, and on the submission and review process within the W3C, please refer to http://www.w3.org/ .
The XML DOM recently moved from the proposed recommendation phase to the recommendation phase, which is the last step in the approval process at the W3C, and is a very stable standard. For more information on the current DOM specification, and on the submission and review process within the W3C, please refer to http://www.w3.org/ .
XSL is currently in the working draft stage in the W3C. It was submitted by ArborText, Inso, and Microsoft in September 1997. Microsoft plans to update its XSL code to track changes as it moves forward in the standard-development process.
XML vocabularies are the elements used in particular applications or data formats -- the definitions of the meanings of those formats. For example, in CDF, element names such as <Schedule>, <Channel>, and <Item> make up the vocabulary for describing collections of pages, when these pages should be downloaded, etc. Vocabularies, along with the structural relationships between the elements, are defined in XML DTDs today, and soon with XML-Data schemas.
The channel definition format is an XML-based data format used in Microsoft Internet Explorer 4.0, for describing Active Channel content and Active Desktop™ components. It is used by thousands of content developers and millions of end users to describe collections of pages and data about pages, such as channel bar display, download behavior, Web page usage, and page-hit logging. For more information on CDF, see the Content & Component Delivery section of the SBN Workshop.
The open software description (OSD) is an XML-based data format, fully supported in Microsoft Internet Explorer 4.01, for advertising and installing software components over the Internet. When new versions of software become available, OSD provides a mechanism to notify the user (a process referred to as publishing). In addition, OSD provides the functionality to describe in great detail how to install ActiveX® Controls and Java packages and class files, adding functionality to the use of .INFs for setup. Microsoft and Marimba Inc. submitted this specification to the W3C in August 1997. For more information, see http://www.microsoft.com/standards/osd/.
The open financial exchange (OFX) is a data format that Microsoft Money and Intuit Quicken personal finance applications use to communicate with financial institutions over the Web. Although it is currently described using SGML, OFX will soon be based on XML.
The resource description framework (RDF), is an XML-based application being developed in the W3C. It brings together ideas from the meta content format, or MCF (technology acquired by Netscape from Apple Computer Inc.) and XML-Data (defined in a proposal recently submitted to the W3C by Microsoft, ArborText, DataChannel, and Inso).
RDF allows for generalized searching of information without application-specific rules, such as those defined in DTDs. RDF allows a complementary view of data through graphs and nodes, rather than through a structured tree, which the current XML technology enables. RDF, together with XML schemas, will provide a standard way for developers to write these relationships down for broad classes of XML elements.
The crucial technologies that will deliver value this year and next are XML for structured data, XML namespaces to make names unique and recognizable, and new XML tags that add meaning to data so smarter search engines can perform better searches.
Many vendors offer support for XML in their products today. See the XML Tools page for a listing of the top third-party vendors.
Microsoft expects a wide variety of applications to be developed in the coming months that convert information currently stored in documents and databases into XML for delivery to the desktop. In addition, Microsoft expects XML-centric databases, rich authoring and application developer tools, and data format-specific tools such as wizards to be developed as new vocabularies are defined.
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