myequivalents is a system to manage cross-references between entities that can be identified by pairs composed of a service name (e.g., EBI's ArrayExpress, Wikipedia) and an accession (e.g., E-MEXP-2514, Barack_Obama). We also support identification of entities via URIs (i.e., the Semantic Web way) and automatic conversion between the two representations.
We plan to add SPARQL access in future (a prototype is already implemented).
Please have a look at the wiki for details.