The parser can operate in two modes:
sgml mode and
mode, as defined by the
dialect(Dialect) option. Regardless
of this option, if the first line of the document reads as below, the
parser is switched automatically into XML mode.
<?xml ... ?>
Currently switching to XML mode implies:
- XML empty elements
<element [attribute...] />is recognised as an empty element.
- Predefined entities
The following entitities are predefined:
- Case sensitivity
In XML mode, names are treated case-sensitive, except for the DTD reserved names (i.e.
- Character classes
In XML mode, underscores (
_) and colon (
:) are allowed in names.
- White-space handling
White space mode is set to
preserve. In addition to setting white-space handling at the toplevel the XML reserved attribute
xml:spaceis honoured. It may appear both in the document and the DTD. The
removeextension is honoured as
xml:spacevalue. For example, the DTD statement below ensures that the
preelement preserves space, regardless of the default processing mode.
<!ATTLIST pre xml:space nmtoken #fixed preserve>
Using the dialect
xmlns, the parser will
interpret XML namespaces. In this case, the names of elements are
returned as a term of the format
If an identifier has no namespace and there is no default namespace it is returned as a simple atom. If an identifier has a namespace but this namespace is undeclared, the namespace name rather than the related URL is returned.
Attributes declaring namespaces (
are reported as if
xmlns were not a defined resource.
In many cases, getting attribute-names as url:name is not desirable. Such terms are hard to unify and sometimes multiple URLs may be mapped to the same identifier. This may happen due to poor version management, poor standardisation or because the the application doesn't care too much about versions. This package defines two call-backs that can be set using set_sgml_parser/2 to deal with this problem.
xmlns is called as XML namespaces are
noticed. It can be used to extend a canonical mapping for later use by
urlns call-back. The following illustrates this
behaviour. Any namespace containing
rdf-syntax in its URL
or that is used as
rdf namespace is canonicalised to
implies that any attribute and element name from the RDF namespace
:- dynamic xmlns/3. on_xmlns(rdf, URL, _Parser) :- !, asserta(xmlns(URL, rdf, _)). on_xmlns(_, URL, _Parser) :- sub_atom(URL, _, _, _, 'rdf-syntax'), !, asserta(xmlns(URL, rdf, _)). load_rdf_xml(File, Term) :- load_structure(File, Term, [ dialect(xmlns), call(xmlns, on_xmlns), call(urlns, xmlns) ]).
The library provides iri_xml_namespace/3 to break down an IRI into its namespace and localname:
- [det]iri_xml_namespace(+IRI, -Namespace, -Localname)
- Split an IRI (Unicode URI) into its Namespace (an IRI) and
Localname (a Unicode XML name, see xml_name/2).
Localname is defined as the longest last part of the IRI that
satisfies the syntax of an XML name. With IRI schemas that are designed
to work with XML namespaces, this will typically break the IRI on the
. Note however that this can produce unexpected results. E.g., in the example below, one might expect the namespace to be http://example.com/images\#, but an XML name cannot start with a digit.
?- iri_xml_namespace('http://example.com/images#12345', NS, L). NS = 'http://example.com/images#12345', L = ''.
As we see from the example above, the Localname can be the empty atom. Similarly, Namespace can be the empty atom if IRI is an XML name. Applications will often have to check for either or both these conditions. We decided against failing in these conditions because the application typically wants to know which of the two conditions (empty namespace or empty localname) holds. This predicate is often used for generating RDF/XML from an RDF graph.
- [det]iri_xml_namespace(+IRI, -Namespace)
- Same as iri_xml_namespace/3, but avoids creating an atom for the Localname.