  We consider the recommendations of the World Wide Web Consortium (W3C) about
RDF framework and its associated query language SPARQL. We propose a new formal
framework based on category theory which provides clear and concise formal
definitions of the main basic features of RDF and SPARQL. We define RDF graphs
as well as SPARQL basic graph patterns as objects of some nested categories.
This allows one to clarify, in particular, the role of blank nodes.
Furthermore, we consider basic SPARQL CONSTRUCT and SELECT queries and
formalize their operational semantics following a novel algebraic graph
transformation approach called POIM.
