Chapter 4. Data Model

HTTP/1.1 has a simple data model: Ultimately, all Web objects are resources, which can be addressed by Uniform Resource Identifiers (URIs). WebDAV extends this data model while still keeping it rather simple.

• A collection is a special kind of resource that contains other resources. As a type of resource, a collection is addressable.

• All resources have properties with names and values, but properties are not independently addressable and do not have URIs.

• Any resource may be locked. Locks are not independently addressable either.

A data model allows clients to have assumptions about the way information will be organized on the server and to use these assumptions to access information on behalf of the user. A consistent data model helps keep protocol design focused and can improve interoperability.

This chapter covers all the components of the model and how they interact. After this, it will become much easier to understand what WebDAV protocol interactions do.

XML has been mentioned before now, but this chapter starts to refer to XML concepts like elements, attributes [Bray00], qualified names, and namespaces [Bray99]. XML is sufficiently human readable that the examples in this book should be digestible by anybody with a passing familiarity with XML, but some of the terminology may be a little daunting. There are many books on XML, both simple and complicated, and many Web sites, tutorials, and articles. For a complete primer, I recommend XML: A Manager's Guide [Dick03].