XML Schema

Chapter 4. Using Predefined Simple Datatypes

W3C XML Schema provides an extensive set of predefined datatypes. W3C XML Schema derives many of these predefined datatypes from a smaller set of “primitive” datatypes that have a specific meaning and semantic and cannot be derived from other types. We will see how we can use these types to define our own datatypes by derivation to meet more specific needs in the next chapter.

Figure 4-1 provides a map of predefined datatypes and the relationships between them.

Figure 4-1. W3C XML Schema type hierarchy

Lexical and Value Spaces

W3C XML Schema introduced a decoupling between the data, as it can be read from the instance documents (the “lexical space”), and the value, as interpreted according to the datatype (the “value space”).

Before we can enter into the definition of these two spaces, we must examine the processing model and the transformations endured by a value written in a XML document before it is validated. Element and attribute content proceeds through the following steps during processing:

Serialization space

The series of bytes that is actually stored in a document (either as the value of an attribute or as a text node) may be seen as belonging to a first space, which we may call the “serialization space.”

Parsed space

The XML 1.0 Recommendation makes it clear that the serialization space is not directly meaningful to applications, ...