Class Schematron

source code

      object --+    
               |    
etree._Validator --+
                   |
                  Schematron

An ISO Schematron validator.

Pass a root Element or an ElementTree to turn it into a validator. Alternatively, pass a filename as keyword argument 'file' to parse from the file system.

Schematron is a less well known, but very powerful schema language. The main idea is to use the capabilities of XPath to put restrictions on the structure and the content of XML documents.

The standard behaviour is to fail on failed-assert findings only (ASSERTS_ONLY). To change this, you can either pass a report filter function to the error_finder parameter (e.g. ASSERTS_AND_REPORTS or a custom XPath object), or subclass isoschematron.Schematron for complete control of the validation process.

Built on the Schematron language 'reference' skeleton pure-xslt implementation, the validator is created as an XSLT 1.0 stylesheet using these steps:

0. (Extract from XML Schema or RelaxNG schema)
1. Process inclusions
2. Process abstract patterns
3. Compile the schematron schema to XSLT

The include and expand keyword arguments can be used to switch off steps 1) and 2). To set parameters for steps 1), 2) and 3) hand parameter dictionaries to the keyword arguments include_params, expand_params or compile_params. For convenience, the compile-step parameter phase is also exposed as a keyword argument phase. This takes precedence if the parameter is also given in the parameter dictionary.

If store_schematron is set to True, the (included-and-expanded) schematron document tree is stored and available through the schematron property. If store_xslt is set to True, the validation XSLT document tree will be stored and can be retrieved through the validator_xslt property. With store_report set to True (default: False), the resulting validation report document gets stored and can be accessed as the validation_report property.

Here is a usage example:

>>> from lxml import etree
>>> from lxml.isoschematron import Schematron

>>> schematron = Schematron(etree.XML('''
... <schema xmlns="http://purl.oclc.org/dsdl/schematron" >
...   <pattern id="id_only_attribute">
...     <title>id is the only permitted attribute name</title>
...     <rule context="*">
...       <report test="@*[not(name()='id')]">Attribute
...         <name path="@*[not(name()='id')]"/> is forbidden<name/>
...       </report>
...     </rule>
...   </pattern>
... </schema>'''),
... error_finder=Schematron.ASSERTS_AND_REPORTS)

>>> xml = etree.XML('''
... <AAA name="aaa">
...   <BBB id="bbb"/>
...   <CCC color="ccc"/>
... </AAA>
... ''')

>>> schematron.validate(xml)
False

>>> xml = etree.XML('''
... <AAA id="aaa">
...   <BBB id="bbb"/>
...   <CCC/>
... </AAA>
... ''')

>>> schematron.validate(xml)
True