Naming and Defining Entities and Attributes › Entity and Attribute Names

Entity and Attribute Names

The most important rule to remember when naming entities is that entity names are always singular. This facilitates reading the model with declarative statements such as “A FLIGHT <transports> zero or more PASSENGERs” and “A PASSENGER <is transported by> one FLIGHT.” When you name an entity, you are also naming each instance. For example, each instance of the PASSENGER entity is an individual passenger, not a set of passengers.

Attribute names are also singular. For example, “person-name,” “employee-SSN,” “employee-bonus-amount” are correctly named attributes. Naming attributes in the singular helps to avoid normalization errors, such as representing more than one fact with a single attribute. The attributes “employee-child-names” or “start-or-end-dates” are plural, and highlight errors in the attribute design.

A good rule to use when naming attributes is to use the entity name as a prefix. The rule here is:

• Prefix qualifies
• Suffix clarifies

Using this rule, you can easily validate the design and eliminate many common design problems. For example, in the CUSTOMER entity, you can name the attributes “customer-name,” “customer-number,” “customer-address,” and so on. If you are tempted to name an attribute “customer-invoice-number,” you use the rule to check that the suffix “invoice-number” tells you more about the prefix “customer.” Since it does not, you must move the attribute to a more appropriate location, such as INVOICE.

You may sometimes find that it is difficult to give an entity or attribute a name without first giving it a definition. As a general principle, providing a good definition for an entity or attribute is as important as providing a good name. The ability to find meaningful names comes with experience and a fundamental understanding of what the model represents.

Since the data model is a description of a business, it is best to choose meaningful business names wherever that is possible. If there is no business name for an entity, you must give the entity a name that fits its purpose in the model.