Several query languages for RDF have been proposed before the World Wide Web Consortium started to standardize SPARQL. Due to the declarative nature of the proposed query languages, a query engine is responsible to choose an efficient evaluation strategy. Although all of the RDF repositories provide query capabilities, some of them disregard declarativeness during query evaluation.
In this paper, we propose a query graph model (QGM) for SPARQL supporting all phases of query processing. On top of the QGM we defined transformations rules to simplify the query specification as a preliminary step of query execution plan generation. Furthermore, the query graph model can easily be extended to represent new concepts.