The codebase for XQS encapsulates two approaches to processing a Schematron schema for validation purposes. Dynamic evaluation, as mentioned above, processes the instructions the schema contains in memory. The other method of compiling a schema produces an XQuery main module, which can be serialized and used for validation, either at the command line or as part of a larger application.

The code for each approach is organized into the respective modules evaluate.xqm and compile.xqm. In broad terms, they each take the same approach to the detail of processing the schema, with successive functions to handle in turn the schema, phases, patterns, rules and assertions.

Figure 3. Schematron schema structure

As might be expected, the main difference between evaluating and compiling is that the evaluation functions are part of the codebase, while those in the compiled schema are generated automatically by functions which are themselves part of the codebase. The following sections outline some implementation details of note.