The Canonical Graph. SSWAP uses a canonical structure of relationships between a web resource (the blue http://webResource icon on the left) and its offering. Specifically, a resource states that it maps some data (sswap:Subject), such as a lookup key into a database, into return data (sswap:Object), such as DNA FASTA sequences. Multiple subject to object and inverse mappings are possible. Blue icons represent RDF "things"--either URLs or blank nodes, orange ovals represent OWL classes, and arrows represent OWL predicates. The class sswap:Graph allows for nested data structures. The full protocol supports an additional sswap:Provider class and other predicates not shown (see http://sswap.info/protocol.jsp).