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.

In the sections which follow we describe notations for describing the properties of
entities and their relationships including cardinality and optionality (the crows
foot and dashing of lines),
exclusion (the exclusion arc), recursion (looping structures), abstraction (nested
boxes), 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 further development including the special treatment of composition relationships,
and thereby their foregrounding,
and the notation for the absolute.

Different features of the notation are described in the sections below :

A number of examples then follow: before introducing the third component of entity modelling: Examples of data modelling: Finally we spell out two constrasting styles of composition structure namely hierarchical structure versus network or matrix structure: