Identifying relationships
Having identified the entities, the next step is to identify all the relationships that exist between these entities. When you identify entities, one method is to look for nouns in the users’ requirements specification. Again, you can use the grammar of the requirements specification to identify relationships. Typically, relationships are indicated by verbs or verbal expressions. For example:
• Branch Has Staff
• Branch IsAllocated VideoForRent
• VideoForRent IsPartOf RentalAgreement
The fact that the users’ requirements specification records these relationships suggests that they are important to the users, and should be included in the model.
Take great care to ensure that all the relationships that are either explicit or implicit in the users’ requirements specification are noted. In principle, it should be possible to check each pair of entities for a potential relationship between them, but this would be a daunting task for a large system comprising hundreds of entities. On the other hand, it’s unwise not to perform some such check. However, missing relationships should become apparent when you check the model supports the transactions that the users require. On the other hand, it is possible that an entity can have no relationship with other entities in the database but still play an important part in meeting the user’s requirements.
kalvinspartan answered the question on July 9, 2018 at 19:16
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