OData is a data access protocol that allows the definition of REST-based data services. Due to the usage of standard technologies (AtomPub, HTTP and JSON), OData has gained widespread attention within the industry lately. Companies such as Microsoft and eBay provide OData interfaces for their applications and services. SAP provides OData support not only for its ERP-system but for the whole Business Suite. In order to simplify the retrieval of data from ERP-systems and to make them available for the integration with the Semantic Web, we present an approach to realize SPARQL endpoints on top of OData interfaces. The work presented in this paper mainly consists of two parts. In the first part, we define an extension of the  Conceptual Schema Definition Language  ( CSDL ) to semantically annotate OData services. In the second part, we adapt the evaluation semantics of SPARQL algebra expressions with regard to graph templates which are defined by the semantically annotated CSDL documents. Based on the adapted evaluation, we can determine the relevant OData services that need to be queried to answer a given SPARQL query. A prototypical implementation shows the feasibility of our approach.
['Marc Kirchhoff', 'Kurt Geihs']
Integrating OData services into the semantic web: a SPARQL interface for OData