Understanding XML Schemas
Editor's note: since the publication of this article the W3C has made significant progress on the XML Schema specification. For an updated reference please see Using W3C XML Schema, published on XML.com November 29, 2000.
|W3C's Schema Working Draft |
6 May 1999
The Schema WD is published in two parts: Part 1: Structures and Part 2: Datatypes (more about each of these in a moment). Note, however, that the WG begins each of these documents with the forthright statement that they are expected to change in substantial ways. At this stage in the game, what's important is to understand the goals and motivations for XML Schemas. Don't sweat the details.
In May, the XML Schema Working Group (WG) published its first Working Draft (WD). Schemas will have a broad impact on the future of XML for two reasons: first because they will define what it means for an XML document to be valid and second because they are a radical departure from Document Type Definitions (DTDs), the existing schema mechanism inherited from SGML.
In this article, I'll explore what schemas are, what validity means, how schemas differ from DTDs, and what new functionality will be gained from adopting them. I'll be using the XML Schemas WD from 6 May 1999 to frame the discussion and as the source for concrete examples.
The following sections cover specific topics in more detail. The sections are independent, so you can read them in whatever order suits you.