This website is an online book, part written as yet, in which entity modelling and data design, both relational and hierarchical, are described from first principles so as to harmonise with and benefit from mathematical type theory and category theory. It features a new theory of relational design supported by open source software implementing the physical data design transformation and other model transformations as well as code generators to support a variety of programming languages.

Entity modelling is saying what is and doing so purposefully — it's a technique and a notation for describing and communicating what is in the world and we set out to present it here from first principles. It enables the representation of conceptual models; its practitioners represent types of entity as labelled boxes and relationships as annotated connections between boxes:

There is no standard notation for entity modelling - different authors use different diagramming styles and models are variously known as entity models, entity-relationship (ER) models or entity relationship attribute (ERA) models. This site promotes a notation that is a further development of a notation used in the SSADM¹ software design methodology and described in a book² by Richard Barker and sometime described as the the Barker-Ellis notation.

There are lots of books and many many web pages describing entity modelling but key differentiating features of the technique as described here are

• the distinction between composition and reference and the top-down layout of diagrams,
• the concept of the scope of a relationship,
• the incorporation of the pullback concept from category theory,
• right first time database design and the elimination of the normalisation step from relational data design.