www.entitylogic.org - entity modelling introduced from first principles - relational database design theory and practice - dependent type theory
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 - 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 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 (i) the distinction between composition and reference and (ii) the concept of the scope of a relationship. The gain is in an expressive power in the conceptual models that carries through into right first time database design by elimination of the normalisation step of relational database 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.
Wrapping Up —The background to this site.