Support for standard query operations. Several papers. From a database
prespective:
Selection: Choosing a document or document element based on content,
structure or attributes. Some argues that the document structure is important
and should not be lost in an abstract view.
Extraction: Pulling out particular elements of a document.
Reduction: Removing selected sub-elements of an element.
Restructuring: Constructing a new set of element instances to hold
queried data. Ordering which is a special case of restructuring. Ranked retrieval
and duplicate removal. Complex and powerful transformation and restructuring
capabilities. Note that XSL lays claim to some of this territory.
Combination: Merging two or more elements into one.
