SchXslt [ʃˈɛksl̩t] – An XSLT-based Schematron processor

SchXslt is copyright (c) 2018–2021 by David Maus <dmaus@dmaus.name> and released under the terms of the MIT license.

SchXslt is a Schematron processor implemented entirely in XSLT. It transforms a Schematron schema document into an XSLT stylesheet that you apply to the document(s) to be validated.

Limitations

As of date SchXslt does not properly implement the scoping rules of pattern (see #135) and phase variables (see #136).

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.

Due to the constrains of XSLT 1.0 and the way rules are implemented it is not possible to use a variable inside a rule context expression of a Schematron using the XSLT 1.0 query binding (see #138).

Schematron enhancements

SchXslt implements the following Schematron 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.

Base URI fixup

Proposal 2

The Schematron specification defines two elements that handle the inclusion of external definitions, include and extends, but does not clarify how this inclusion effects relative URI references in the inserted content.

This proposal implements base URI fixup as defined in XInclude 4.5.5.

Base URI fixup is enabled by default. You can disable it by setting the parameter schxslt.base-uri-fixup to boolean false when calling the stylesheets that performs inclusions. For convenience, you can run the stylesheet include-no-baseuri-fixup.xsl which runs the inclusion phase with base URI fixup turned off.

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 referencable by the @rule attribute of extends.

Addition 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 (XSLT 3.0)
• xsl:import (XSLT 1.0, XSLT 2.0, XSLT 3.0)
• xsl:import-schema (XSLT 2.0, XSLT 3.0)
• xsl:include (XSLT 1.0, XSLT 2.0, XSLT 3.0)
• xsl:use-package (XSLT 3.0)

Installation

Depending on your environment there are several ways to install SchXslt.

• Starting with version 1.5 every release on this repository's release page provides a ZIP file with just the XSLT stylesheets. This page also provides a ZIP file with the XSLT stylesheets and two XProc 1.0 steps. Just download and unzip.

• A Java package is published to Maven Central. Use it with Maven or the Java dependency management tool of your choice.

• If you use BaseX or eXist you can download installable XQuery modulesq from this repository's release page as well.

Using SchXslt

XSLT Stylesheets

The simplest way to use SchXslt is to download the ZIP file with just the stylesheets from the releases page. To validate documents with your Schematron you first transform it with the pipeline-for-svrl.xsl stylesheet. This creates the XSL transformation that creates a validation report when applied to a document.

Java applications

To use SchXslt in your Java application define the following Maven dependency:

<dependency>
  <groupId>name.dmaus.schxslt</groupId>
  <artifactId>schxslt</artifactId>
  <version>{VERSION}</version>
</dependency>

Where {VERSION} is replaced with the current SchXslt version.

Also take a look at SchXslt Java, a set of Java classes for Schematron validation with SchXslt.

XQuery

The XQuery module provides a function schxslt:validate() that validates a document and returns a validation report expressed in the Schematron Validation Report Language (SVRL). You import the module using its namespace URI.

import module namespace schxslt = "https://doi.org/10.5281/zenodo.1495494";

let $document := <ex:example xmlns:ex="https://example.com/ns"/>
let $schema :=
  <sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
    <sch:pattern>
      <sch:rule context="/">
        <sch:assert test="true()">Always true</sch:assert>
      </sch:rule>
    </sch:pattern>
  </sch:schema>

return
  schxslt:validate($document, $schema)

Ant

TBD

Command line

TBD

Building

SchXslt uses the Maven build tool to create installable packages. To create the packages for yourself clone this repository, install Maven and run it with the package phase.

dmaus@carbon ~ % git clone --recursive https://github.com/schxslt/schxslt.git
Cloning into 'schxslt'...
remote: Enumerating objects: 450, done.
remote: Counting objects: 100% (450/450), done.
remote: Compressing objects: 100% (298/298), done.
remote: Total 3789 (delta 172), reused 374 (delta 111), pack-reused 3339
Receiving objects: 100% (3789/3789), 470.87 KiB | 1.05 MiB/s, done.
Resolving deltas: 100% (1607/1607), done.

dmaus@carbon ~ % mvn package

This runs the unit tests and creates the following files:

• core/target/schxslt-{VERSION}.jar (Java archive)
• core/target/schxslt-{VERSION}-xslt-only.zip (ZIP file with stylesheets)
• exist/target/schxslt-exist-{VERSION}.xar (XQuery package for eXist)
• basex/target/schxslt-basex-{VERSION}.xar (XQuery package for BaseX)

Where {VERSION} is replaced with the current SchXslt version.