RELAX NG

Chapter 5. Flattening the First Schema

If you look at the structure of the Russian doll-style schema, you’ll see that it follows the structure of the instance document it applies to, as shown in Figure 3-1. Writing the first schema has pretty much been limited to inserting text, element, or attribute elements into the schema each time a text node, element, or attribute was encountered in the instance document. This method of creating schemas can be seen as a serialization of the XML infoset (i.e., of the structure available in the document) and could, therefore, be easily automated.

Tip

Automated serialization is the principle behind Examplotron, a program described in Chapter 14.

There are a couple of drawbacks to modeling documents with the Russian doll-style schemas, however. First, they aren’t modular and therefore become difficult to read and maintain when documents are large or complex. Second, they can’t represent recursive (self-referencing) models. (Lists that may themselves contain lists are a common case of this model.)

The lack of modularity can be seen in a document as simple as the first schema, shown in Example 3-1. There’s a name element that uses the same model within both the character and author elements.

Figure 5-1 shows how, in the first schema, you need to give the definition of what name means in each context:

Figure 5-1. Two different definitions of name in the ...