Data Modelling Symbols
Data modelling uses a standard set of symbols to represent each of these defined data groups, and then proceeds by establishing the relationships between them. The first of these symbols is the soft-box entity symbol, eg:
An entity is something about which data will be stored in the system under consideration. In this example the data group invoice can be identified as a system entity.
The other main component on a data model is the relationship line. A relationship is an association between two entities to which all of the occurrences of those entities must conform.
A line that joins the two entities to which it refers represents the relationship. This line represents two reciprocal relationships: that of the first entity with respect to the second, and that of the second entity with respect to the first.
Next: Relationships between Entities