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SchXslt2 Schematron to XSLT 3.0 transpiler

SchXslt2 is the second iteration of SchXslt, a modern XSLT-based implementation of the ISO Schematron validation language (ISO/IEC-19757:3).

SchXslt2 Schematron to XSLT 3.0 transpiler is copyright by David Maus <[email protected]> and released under the terms of the MIT license.

Installating

Every release provides a ZIP file with just the XSLT transpiler for you to download and extract.

In addition, a Java package is published to Maven Central for use with Maven or the Java dependency management tool of your choice.

Usage

Use the transpiler to create an XSLT transformation that processes a document and returns a SVRL (Schematron Validation Reporting Language) report.

Transpiler parameters

schxslt:debug as xs:boolean

Enable or disable debugging. When debugging is enable, the validation stylesheet is indented. Defaults to false.

schxslt:phase as xs:string?

Name of the validation phase. The value '#DEFAULT' selects the pattern in the sch:schema/@defaultPhase attribute or '#ALL', if this attribute is not present. The value '#ALL' selects all patterns. Defaults to '#DEFAULT'.

schxslt:streamable as xs:boolean

Set to boolean true to create a streamable validation stylesheet. This does not check the streamability of XPath expressions in rules, assertions, variables etc. It merely declares the modes in the validation stylesheet to be streamable and removes the @location attribute from the SVRL output when no location function is given because the default fn:path() is not streamable. Defaults to false.

schxslt:location-function as xs:string?

Name of a function f($context as node()) as xs:string that provides location information for the SVRL report. Defaults to fn:path() when not set.

schxslt:expand-text as xs:boolean

When set to boolean true, the validation stylesheet globally enables text value templates and you may use them in assertion or diagnostic messages. Defaults to false.

schxslt:fail-early as xs:boolean

When set to boolean true, the validation stylesheets stops as soon as it encounters the first failed assertion or successful report. Defaults to false.

schxslt:terminate-validation-on-error as xs:boolean

When set to boolean true, the validation stylesheets terminates the XSLT processor when it encounters a dynamic error. Defaults to true.

Enhancements

Typed variables

Proposal 1

The Schematron specification does not allow for annotating variables with the expected type of its value. Type annotations are helpful to make the most of XSLT 3.0. Using them is current best practice.

This proposal adds support for an @as attribute on variable declarations.

Global abstract rules

Proposal 3

The Schematron specification limits the the reuse of abstract rules to the current pattern element. The @href attribute on extends was introduced in 2016 to overcome this limitation but requires a schema author to externalize abstract rules for them to be used.

This proposal extends Schematron with a top-level rules element to hold abstract rules that are globally referable by the @rule attribute of extends.

Additional XSLT elements

Proposal 4

The Schematron specification allows the XSLT elements function and key to be used in a Schematron schema. This makes sense because both are required to set up the query language environment. The key element prepares data structures for the key() function and the function element allows the use of user defined functions.

This proposal adds support for the following XSLT elements:

  • xsl:accumulator
  • xsl:import
  • xsl:import-schema
  • xsl:include
  • xsl:use-package

Declare abstract pattern parameters

To address the shortcomings discussed in Proposal 8 SchXslt2 supports the sch:param element as child of an abstract pattern to declare an abstract pattern parameter.

As of version 1.2 an abstract pattern parameter may also declare a default value in a @value attribute.

<sch:pattern id="a-001" abstract="true">
  <sch:param name="_placeholder" value="default"/>
  ...
</sch:pattern>

If at least one sch:param element is present, the transpiler terminates with an error if a declared parameter is not provided, and if a provided parameter ist not declared.

Introspection

Expressions in the validation stylesheet can access the effective phase it was compiled for by using the global variable Q{http://dmaus.name/ns/2023/schxslt}phase.

Logging dynamic errors

Dynamic errors during validation are logged by a svrl:error element (see Proposal 69.

Unless the static parameter schxslt:terminate-validation-on-error is set to false the validation stylesheet still terminates the XSLT processor.

Limitations

SchXslt2 does not implement proper scoping rules of pattern and phase variables. Schema, pattern, and phase variables are all implemented as global XSLT variables. As a consequence, the name of a schema, pattern, or phase variable MUST be unique in the entire schema.