An XML Schema is an XML-based syntax for defining how an XML document is marked up. XML Schema is a schema specification recommended by Microsoft and it has many advantages over document type definition (DTD), the initial schema specification for defining an XML model. DTDs have many drawbacks, including the use of non-XML syntax, no support for datatyping, and non-extensibility. For example, DTDs do not allow you to define element content as anything other than another element or a string. For more information about DTDs, see the Worldwide Web Consortium (W3C) XML Recommendation. XML Schema improves upon DTDs in several ways, including the use of XML syntax, andsupport for datatyping and namespaces. For example, an XML Schema allows you to specify an element as an integer, a float, a Boolean, a URL, and so on.

Dare Obasanjo discusses various aspects of W3C XML Schema and how they are affected by namespaces. Topics covered include proper usage of the targetNamespace, elementFormDefault and attributeFormDefault attributes, as well as the include, import, and redefine elements within a schema.

Microsoft today announced the addition of the Microsoft Office Visio 2003 XML Reference Schema to its open and royalty-free documentation and license program that was initially unveiled in November 2003. Microsoft Office Visio 2003 is the diagramming and data visualization tool in Microsoft Office 2003. Microsoft is providing the complete description of the Visio Extensible Markup Language (XML) file format to enable organizations to access information captures in their Visio diagrams and to integrate with other XML-enabled applications, such as customer relationship management (CRM) and enterprise resource planning (ERP) systems. Extensive support of XML in the Microsoft Office suite will allow Office applications to create, view and edit structured data stored in disparate systems.

Microsoft Corp. today announced the addition of the XML schema used by Microsoft® Office Visio® 2003, DataDiagramML, to the Microsoft Open and Royalty-Free Office 2003 XML reference schema program announced in November 2003. Through the Microsoft documentation and a royalty-free license, customers and partners can take advantage of the XML schema in its diagramming and data visualization tool. The availability of the Visio schema builds on Microsoft's commitment to XML by providing a complete and W3C-compliant description of the Visio Extensible Markup Language (XML) file format, enabling organizations to access information captured in their Visio diagrams and use it with other XML-enabled applications, such as customer relationship management (CRM) and enterprise resource planning (ERP) systems, as part of their business processes. While Microsoft is providing this documentation in an effort to aid solution providers and in-house developers who want to create Visio solutions, some early adopters already have begun developing solutions with Visio 2003, and have touted DataDiagramML's usefulness in creating data visualization solutions.

Now that you understand more about namespaces, you're ready to take a deeper look at the process of XML Schema validation. Although a full treatment of XML Schema is beyond the scope of this tutorial, this section will show you the steps you need to take to validate an XML document using an XML Schema definition. (You can also examine the sample programs that are part of the JAXP download. They use a simple XML Schema definition to validate personnel data stored in an XML file.)

The XML developer who needs to validate documents as part of application flow may choose to begin by writing W3C XML Schema for those documents. This is natural enough, but W3C XML Schema is only one part of the validation story. In this article, we will discover a multiple-stage validation process that begins with schema validation, but also uses XPath and XSLT to assert constraints on document content that are too complex or otherwise inappropriate for W3C XML Schema.

This document describes the various releases of the XML Spec schema and stylesheets.

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).

This is a small FAQ list about XShema.

Content model declarations are made within Model sub-element of the declaration for the element to which they apply. Model elements may appear inside XSchema elements for reusability, documentation, and reference, but will need to be linked to particular element declarations through mechanisms not yet defined (most likely XLink). All content model declarations have an optional id value for reference.

Attribute declarations are made with XSC:AttDef elements nested inside of the element declaration. The data type of an attribute is defined with a sub-element, as is a declaration of whether or not it is required and a possible default value.

XSchema provides areas in which XSchema developers can provide supplemental information and metadata regarding XSchema components in both human- and machine-readable formats. Human-readable information is provided through the use of a subset of HTML that conforms to XML syntax, while machine-readable information may be provided through the XSC:More element.

Extensible Markup Language (XML) uses notation inherited from the Standard Generalized Markup Language (SGML) to represent document structures and inclusions in its Document Type Definitions (DTDs). While this achieves considerable compatibility with SGML, it makes it impossible to extend the capacities of a DTD beyond those provided in SGML, requires developers to understand two different syntaxes for documents and DTDs, and forces tool builders to create a separate set of tools for managing DTDs.

XSchema uses namespaces for its own operations and also supports schemas that take advantage of namespace facilities. XSchema processors are responsible only for elements that use the XSchema namespace appropriate to the version of XSchema they are processing. (This namespace is identified with the prefix XSC: throughout this document; see 3.3 below for alternatives.) Information in other namespaces may be passed to other applications as the processor deems appropriate.

This section describes the XSchema document syntax. The XSchema document is an XML document containing a single XSchema element in which information describing the schema is nested. The XSchema element must be preceded by an XML declaration and may be preceded by other declarations, comments, and processing instructions.

XSchema documents shall use XML document syntax, using element nesting and attributes to describe all constraints that may be verified by a processor using XSchema.

Let's list the advantages of XSchema 1.0 [i.e. direct transliteration from DTD to XSchema and back]. It can be parsed and used with any XML-aware tool (e.g. SAX can extract elements).

Validate XML with XML schema.