7.3: Attributes

Attributes are the characteristics that describe entities and relationships. For example, a Student entity may be described by attributes including:

• • student number
  • name
  • first name
  • last name
  • address
  • date of birth
  • gender

An Invoice entity may be described by attributes including:

• • invoice number
  • invoice date
  • invoice total

A common convention for naming attributes is to use singular nouns. Further, a naming convention may require one of:

• • All characters are in upper case.
  • All characters are in lower case.
  • Only the first character is in upper case.
  • All characters are lower case, but each subsequent part of a multipart name has the first character capitalized

Using the last convention mentioned, some examples of attribute names:

• • lastName for last name
  • empLastName for employee last name
  • deptCode for department code
  • prodCode for product code
  • invNum for invoice number

In practice a naming convention is important, and you should expect the organization you are working for to have a standard approach for naming things appearing in a model. A substantial data model will have tens, if not into the hundreds, of entity types, many more attributes and relationships. It becomes important to easily understand the concept underlying a specific name; a naming convention can be helpful.

There are many ways we can look at attributes including whether they are atomic, composite, single-valued, etc. We consider these next.