# Barker's Notation

## What is Barker's Notation?

**Barker's notation** refers to the ERD notation developed by Richard Barker, Ian Palmer, Harry Ellis et al. whilst working at the British consulting firm CACI around 1981. The notation was adopted by Barker when he joined Oracle and is effectively defined in his book Entity Relationship Modelling as part of the CASE Method series of books. This notation was and still is used by the Oracle CASE modelling tools. It is a variation of the "crows foot" style of data modelling that was favoured by many over the original Chen style of ERD modelling because of its readability and efficient use of drawing space.

When looking at different kinds of ERD notations, it is hard not to come across Barker’s ERD notation, which is commonly used to describe data for Oracle. Richard Barker and his coworkers developed this ERD notation while working at the British consulting firm CACI around 1981, and when Barker joined Oracle, his notation was adopted. Let’s take a closer look at Barker’s syntax.

The most important components in the ERD diagram are:

- entities, which can be thought of as physical objects or elements that can be uniquely identified, and
- relationships, which capture how entities are related to one another.

The notation has features that represent the properties of relationships including cardinality and optionality (the crows foot and dashing of lines), exclusion (the exclusion arc), recursion (looping structures) and use of abstraction (nested boxes).

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## References