Entity Modelling

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


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 ...

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.

...with a Difference

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.


On this site you will find:

Perspective An Introductory Perspective that seeks to locate entity modelling so that it is not seen as an isolated discipline. Entity modelling evolved in the 1960s an 70s as an abstract way to describe databases (more specifically the structure of databases), and so it is, but its utility goes further than this as described here.

Tutorial Part One The Entity Modelling Tutorial Part One - Entities, Relationships and Attributes which introduces from first principles a good part of the basic notation.

English Sentence Structure An Extended Example - the Structure of English Sentences which is an extended example of modelling using the notation introduced upto this point.

Tutorial Part Two The Entity Modelling Tutorial Part Two - Advanced Topics including Relationship Scope which is a tutorial describing use of the notation for modelling and introducing the important concept of relationship scope.

Blog A Blog on Entity Modelling, Data Modelling and Logic. Some further thoughts on data modelling, entity modelling and logic.

The AuthorAbout the Author.

1 Goodland, Mike and Slater, Caroline. SSADM Version 4: A prractical Approach. McGraw Hill Publishing Co., 1995.
2 Barker, Richard. Case Method: Entity Relationship Modelling. Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA, 1990.