One or many

How to read it

The crow’s foot, the fork of three lines nearest the entity box, sets the maximum at many. The bar just outside it sets the minimum at one, so the relationship is mandatory. Read from the other end, the line says: each record there has one or more of these.

The outer mark is what tells this apart from Zero or many: a bar here, an open circle there.

Also searched as: mandatory many, one or many symbol, one to many crow’s foot.

Where the crow’s foot comes from

The fork is credited to Gordon Everest, who used it in a 1976 paper, “Basic Data Structure Models Explained With A Common Example”, given at the Fifth Texas Conference on Computing Systems. Everest called the mark an “inverted arrow”, and later a “fork”; “crow’s foot” is the nickname it picked up from its shape. His own publication list describes the paper as “thought to be the first” to use the fork for multiplicity. A related notation, developed at the British consultancy CACI and promoted by Richard Barker, was adopted by Oracle for its CASE*Method and is still used by Oracle’s design tools.

Look-alikes

The Zero or many mark has a circle where this one has a bar. The One and only one mark has two bars and no fork.

Differences by notation

In (min, max) notation this is (1,N), and in UML-style multiplicity 1..N, often written 1..*. Barker’s notation draws it as a solid half-line, “must be”, with a crow’s foot, “one or more”.