E-R DIAGRAMS

The overall logical structure of a database can be expressed graphically by E-R diagram. The entity-relationship model can be conveniently represented in a pictorial form using drawing tools.

1. Rectangles: represent entity set.

2. Ellipses: represent attributes.

3. Diamonds: represent relationships among entity sets.

4. Lines: link attributes to entity sets and entity sets to relationships.

5. Key attributes: have their names underlined.

6. Derived attributes: are shown in dotted ovals.

7. Double rectangular: represent weak entity types and their identifying relationship are shown by double diamonds.

8. Dotted line: The partial key of the weak entity type.