Today in class, we talked about some important terminology for databases. This is my attempt at defining them in my own words.
- Entity – same as an entity type below, which can also be called an entity class.
- Entity type (class) – this is the thing we’re recording information about. It can be a person, place, thing, event, or concept.
- Instance – this is one entry in the database of an entity type. For example, if the entity is “Place,” then the instance could be “Neyland Stadium.”
- Attribute – this is something that describes an instance. In the example of the instance “Neyland Stadium,” attributes could be “Address,” “Elevation,” Number of Seats,” etc.
- Types of attributes – there are many types of attributes. Below are explanations of each:
Atomic – an attribute that can not be broken down into smaller pieces. For example, an attribute for a city, “Knoxville,” can not be broken down into smaller pieces.
Composite – an attribute that could be broken down into smaller pieces. For example, 7917 Eldin Way, Powell, TN 37849, could be further broken down into attributes for Street Address, City, State, and ZIP Code.
Single valued – an attribute that can only have one value. For example, a student’s SSN or date of birth.
Multivalued – an attribute that can have more than one value. For example, a student’s major in college or a book’s author(s).
Derived – an attribute that is calculated from other attributes. For example, a student’s GPA or age.
Key – an attribute that is a unique identifier for an entity. For example, a student’s student ID or SSN.