Various ontologies are available defining the semantics of digital identity information. Due to the rise in use of lowercase semantics, such ontologies are now used to add metadata to digital identity information within web pages. However concepts exist in these ontologies which are related and must be mapped together in order to enhance machinereadability of identity information on the web. This paper presents the Social identity Schema Mapping (SISM) vocabulary which contains a set of mappings between related concepts in distinct digital identity ontologies using OWL and SKOS mapping constructs.