I.2.6 - The Entity-Relationship diagrams

The collection of ESets, RSets and their properties relevant for a given problem is called a SCHEMA. An ER diagram is a graphical representation of a schema, and the original form of the ER diagrams, as defined by Chen, features:

ESet as a rectangular box with the ESet name inside
RSet as a lozenges with a line connecting it to each ESet that participates in the relationship. The arity is written by the line

and is as shown in Figure 6

                                      
      +------------+           / \           +------------+
      |            |          /   \          |            |
      |  Person    |_________/works\_________|  Project   |
      |            |    m    \ on  /   n     |            |
      |            |          \   /          |            |
      +------------+           \ /           +------------+

Figure 6

Entity Relationship Diagram

The literature suggests several notations, for example: a bubble replacing the lozenge, partiality represented by a small bar crossing the junction line near the ESet, arity being 1/more represented by single/double headed arrows along the junction line ( pointing into or away from the ESet )and attributes listed inside or outside the box.

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SF and PP - CERN PTG - ADAMO Reference Manual for Version 3.3 - 13 Dec 93