XML Standards News; XSchema, XHTML, XML Stylesheet Association and SVG

XSchema Requirements Note Posted

The first requirements document for the W3C XSchema work hs been posted at http://www.w3.org/TR/1999/NOTE-xml-schema-req-19990215 on February 15, 1999. The document was authored by Ashok Malhotra (petsa@us.ibm.com) for IBM and Murray Maloney (murray@muzmo.com) for Veo Systems Inc.

This document specifies the purpose, basic usage scenarios, design principles, and base requirements for an XML schema language. The scope of the work of this group includes the definition of structural schemas, a mechanism somewhat analogous to DTDs for constraining document structure (order, occurrence of elements, attributes). In addition, specific goals beyond DTD functionality are identified within the scope of this work. Examples include the integration of schemas with namespaces, the definition of incomplete constraints on the content of an element type, and the integration of structural schemas with primitive data types. The working group will also tackle the specification of inheritance. The Working Group will define a process for checking to see that the constraints expressed in a schema are obeyed in a document (schema-validation). Also the relationship between schema-validity and validity as defined in XML 1.0 will be defined.

According to this initial document, "The XML schema language shall be: more expressive than XML DTDs; expressed in XML; self-describing; usable by a wide variety of applications that employ XML; straightforwardly usable on the Internet; optimized for interoperability; simple enough to implement with modest design and runtime resources; and coordinated with relevant W3C specs (XML Information Set, Links, Namespaces, Pointers, Style and Syntax, as well as DOM, HTML, and RDF Schema."

XHTML Working Draft

XHTML 1.0, a reformulation of HTML 4.0 as an XML 1.0 application, and three namespaces corresponding to the ones defined by HTML 4.0 was posted by W3C on February 24, 1999. XHTML differs from HTML in two significant ways. First, although XHTML is based on the current HTML tag set, it is designed to be extensible. This extensibility relies upon the XML requirement that documents be well-formed. Under SGML (hence HTML), the addition of a new group of elements would mean alteration of the entire DTD. In an XML-based DTD, all that is required is that the new set of elements be internally consistent and well-formed to be added to an existing DTD. So XML greatly eases the development and integration of new collections of elements into a tag set such as HTML. Second, XHTML is designed for portability. According to the Draft, "There will be increasing use of non-desktop user agents to access Internet documents. Some estimates indicate that by the year 2002, 75% of Internet document viewing will be carried out on these alternate platforms. In most cases these platforms will not have the computing power of a desktop platform, and will not be designed to accommodate ill-formed HTML as current user agents tend to do. Indeed if these user agents do not receive well-formed XHTML, they may simply not display the document."

You can learn more about XHTML by linking to the Working draft at http://www.w3.org/TR/WD-html-in-xml.

Style/XML Becomes a PR

On January 14, 1999 the "Associating stylesheets with XML documents Version 1.0 " by James Clark became a W3C Proposed Recommendation. According to the specification, "This document allows a stylesheet to be associated with an XML document by including one or more processing instructions with a target of xml-stylesheet in the document's prolog. "

According to this PR, Stylesheets can be associated with an XML[XML10] document by using a processing instruction whose target is xml-stylesheet.This processing instruction follows the behaviour of the HTML 4.0 <LINK REL="stylesheet">. For example, the HTML link statement "<LINK href="mystyle.css" rel="stylesheet" type="text/css">" is equivalent to te XML "<?xml-stylesheet href="mystyle.css" type="text/css"?>" processing instruction.

If you are anxious to view XML and control the style, this new PR will prove highly useful. You can check it out at http://www.w3.org/TR/PR-xml-stylesheet.

Scalable Vector Graphics Becomes a WD

On February 11, 1999, Scalable Vector Graphics (SVG) Specification became a W3C Working Draft. Jon Ferraiolo jferraio@adobe.com, served as editor for the new graphics specification. Among the authors were John Bowler (Microsoft), Andrew Donoho (IBM), Jerry Evans (Sun Microsystems), Scott Furman (Netscape Communications Corporation), Peter Graffagnino (Apple), Lofton Henderson (Inso Corporation), Alan Hester( Xerox Corporation), as well as representatives from Corel, Visio, Macromedia, and Quark.

SVG provides a language for describing two-dimensional graphics in XML. SVG describes vector graphic shapes (e.g., paths consisting of straight lines and curves), images and text. SVG enables us to group, style, transform and composite graphic objects into previously rendered objects. SVG drawings can be dynamic and interactive.The feature set includes nested transformations, clipping paths, alpha masks, filter effects, template objects and extensibility. SVG works with the Document Object Model (DOM) to allow for vector graphics animation via scripting. A rich set of event handlers such as onmouseover and onclick can be assigned to any SVG graphical object. Because of its compatibility and leveraging of other Web standards, features like scripting can be done on HTML and SVG elements simultaneously within the same Web page.

The main goal of this draft specification is to illustrate progress within the SVG working group and to solicit public review and feedback. The SVG working group has achieved significant progress toward translating the SVG requirements into an SVG specification. It is important to understand that there is much work to be done and that it is likely that significant changes to the SVG specification will occur before a Proposed Recommendation is delivered by the working group. You can get involved by checking the W3C site at http://www.w3.org/TR/WD-SVG.

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