Research of protein-protein interactions produce vast quantities of data and there exists a large number of databases with data from this research. Many of these databases offers the data for download on the web in a number of different formats, many of
Extensible Markup Language (XML) has been the standard for persistent data storing and data interchange via the Internet, due to its openness, self-descriptiveness and flexibility. As such, more and more data have been converted into XML format or handled in XML format,
XML data is often accompanied by type information, usually expressed by some schema language. Sometimes XML data can be related to ontologies defining classes of objects, such classes can also be interpreted as types. Type systems proved to be extremely useful in
The work presented in this thesis is related to XML which is a dominant standard on the Web used to encode data. In order to retrieve data from the Web, query languages are needed. A well known standard for querying XML data