The XML-QL data model
XML-QL works on an abstraction, called an XML graph, of the concrete XML document:
- comments and processing instructions are ignored;
- the relative order of elements is ignored;
- every node has an ID (autogenerated, if necessary);
- all leaves are character data.
XML graphs are obtained from XML documents but are also generated by
queries.
A graph is mapped back into an XML document by choosing arbitrary orderings of
element sequences.
This abstraction is very similar to that from tables to relations: disregard the order of
tuples and attributes.
