els; H.2.3:[Languages]: Query languages; H.2.4:[Systems]:

Not many XML information retrieval (IR) systems exist that allow easy addition of and switching between di®erent IR models. Especially for the scienti¯c environment where building a system takes a lot of time and keeps researchers away from the real work, i.e., investigating what is the most e®ective IR model, a platform that would provide this func-tionality would be ideal. For this reason we developed such an XML IR system. It is centered around a logical algebra, named score region algebra (SRA), that enables transpar-ent speci¯cation of IR models for XML databases (see [1] for more details). The transparency is achieved by a possibility to instanti-ate various retrieval models, using abstract score functions within algebra operators, while logical query plan and op-erator de¯nitions remain unchanged. Our algebra operator