Relational Technologies, Metadata and RDF

Metadata plays an important role in successfully understanding and querying data on the web. A number of metadata management solutions have already been developed but each is tailored to specific kinds of metadata. The Resource Description Framework (RDF) is a generic, flexible and powerful model which is becoming the de-facto standard for metadata representation on the Web. Its adoption has created an exponential growth of the amount of available RDF data calling for efficient management solutions. Instead of designing such solutions from scratch, it is possible to invest on existing relational technologies by exploiting their long presence and maturity. Relational technologies can offer efficient storage and high performance querying at relatively low cost. Unfortunately, the principles of the relational model are fundamentally different from those of RDF. This difference means that specialized storage and querying schemes need to be put in place in order to use relational technologies for RDF data. In this work we provide a comprehensive description of these relational RDF storage schemes and discuss their advantages and limitations. We believe that through carefully designed schemes, it is possible to achieve sophisticated high performance systems that support the full power of RDF and bring one step closer the materialization of the Semantic Web vision.