]> 1 0 A required class. In the concept of a service mapping an input to an output, the sswap:Subject corresponds to the input. The property sswap:mapsTo explicitly demarcates the mapping (or transformation) from this input to its output. One can also use sswap:mapsTo to describe inverse mappings where the stated relationship is *from* a sswap:Object to a sswap:Subject. Required predicates: <none> Optional predicates: mapsTo metadata While the sswap:mapsTo predicate is not strictly required, there must be at least one mapsTo relation from either a sswap:Subject to a sswap:Object or a sswap:Object to a sswap:Subject (designating an inverse mapping). In most cases, services will use the former to express their mapping. SSWAP classes use recognizable patterns to express required and optional predicates. Basically, cardinality constraints on predicates within an owl:equivalentClass block describe required predicates, while the same inside rdfs:subClassOf blocks describe optional predicates. This model can be used by any service in its own Resource Description Graph to express required and optional arguments. For a full discussion please see http://sswap.info/protocol?selected=parametersDoc.