In Pigott and Hobbs (2009), we introduced such a knowledge representation
formalism, the functional entity relationship diagram (FERD), which comprises a set of
extensions to the industry standard ERD established by Chen (1976a, b). The diagrams
(FERDs) consist of nodes representing these functional entities, edges representing
the relationships between them, and modified heads and tails of these edges to
indicate the type of functional entity. The formalism is compatible with a standard
ERD. Where the additional features are not required, standard ERD representation is
used. We review and extend the FERD formalism in the next sections.