Table of contents

Appendices

4 Schemas and Namespaces: Access and Composition

This chapter defines the mechanisms by which this specification establishes the necessary precondition for assessment, namely access to one or more schemas. This chapter also sets out in detail the relationship between schemas and namespaces, as well as mechanisms for modularization of schemas, including provision for incorporating definitions and declarations from one schema in another, possibly with modifications.

[Conformance] describes three levels of conformance for schema processors, and [Schemas and Schema-validity Assessment] provides a formal definition of assessment. This section sets out in detail the 3-layer architecture implied by the three conformance levels. The layers are:

1. The assessment core, relating schema components and instance information items;

2. Schema representation: the connections between XML representations and schema components, including the relationships between namespaces and schema components;

3. XML Schema web-interoperability guidelines: instance->schema and schema->schema connections for the WWW.

Layer 1 specifies the manner in which a schema composed of schema components can be applied to in the assessment of an instance element information item. Layer 2 specifies the use of [schema] elements in XML documents as the standard XML representation for schema information in a broad range of computer systems and execution environments. To support interoperation over the World Wide Web in particular, layer 3 provides a set of conventions for schema reference on the Web. Additional details on each of the three layers is provided in the sections below.