Entity Modelling

www.entitymodelling.org - entity modelling introduced from first principles - relational database design theory and practice - dependent type theory

This chapter is a tutorial on the use of entity modelling notation.

Previously, in types of things, we introduced boxes
as the diagrammatic representation of types of entities. In the sections which
follow we describe
the conventions for describing
the properties of the differing types of
entities and their inter-type relationships including relationship cardinality
and optionality (the crows foot and dashing of lines),
relationship disjunction (the exclusion arc), recursion (looping structures), type
generalisation (nested boxes) and the representation
of the absolute (diagram root).
The notation is as used in the SSADM method as described,
for example, in Richard Barker's
book^{1},
but with some refinements supported by additional notation and diagramming conventions
including one
that distinguishes and foregrounds composition relationships.