Importing and Exporting Schema Component Models
From version 9.0, Saxon provides the ability to export or import a compiled schema. The export format is an XML
file, known as an SCM file (for schema component model). Exporting a schema in SCM format makes it quicker to reload
when the same schema is used again. It is also a format that is easier for programs to analyze, in comparison with
raw XSD schema documents.
The simplest way to create an SCM file is from the command line, using the
command with the
-scmout option. This is described here. Alternatively,
an SCM file can be generated programmatically using the
exportComponents() method of the
which is described in the JavaDoc. The serializer is unselective: it will output an SCM containing all the schema components
that have been loaded into the Configuration, other than built-in schema components.
An SCM file can be imported using the
-scmin option of the
It can also be loaded programmatically using the
SchemaModelLoader class. For example:
SchemaModelLoader loader = new SchemaModelLoader(config);
loader.load(new StreamSource(new File("input.scm")));
A schema loaded in this way is then available for all tasks performed using this Configuration, including validation
of source documents and compiling of schema-aware queries and stylesheets. In particular, it can be used when
compiled queries are run under this Configuration.
Schema Component Models can also be imported and exported using the
exportComponents() methods of the
SchemaManager in the s9api interface.
The structure of an SCM file is defined in the schema
scmschema.xsd which is available
in the directory
samples/scm/ in the
saxon-resources download file. This is
annotated to explain the mappings between elements and attributes in the SCM file and components and properties
as defined in the W3C XML Schema Specification. The same
directory contains a file
scmschema.scm which contains the schema for SCM in SCM format.
The SCM file includes a representation of the finite state machines used to validate instances
against a complex type. This means that the FSM does not need to be regenerated when a schema is loaded
from an SCM file, which saves a lot of time. However, it also means that the SCM format is not currently
suitable as a target format for software-generated schemas. A variant of SCM in which the finite state
machines can be omitted may be provided in a future release.