The Semantic Web aims at building cross-domain and distributed databases across the Internet. SPARQL is a standard query language for such databases. Evaluating such queries is however NP-hard. We model SPARQL queries in a declarative way, by means of CSPs. A CP operational semantics is proposed. It can be used for a direct implementation in existing CP solvers. To handle large databases, we introduce a specialized and efficient light solver, Castor. Benchmarks show the feasibility and efficiency of the approach.