Database Reference
In-Depth Information
a universal level, there are certain concepts common to all companies such as
Customer
,
Product
, and
Employee
.
Making the scope slightly narrower, a given industry may have certain unique concepts.
Phone Number
, for example, will be a valid concept for a telecommunications company
but perhaps not for other industries such as manufacturing. In the publishing world,
Author
,
Title
, and
Order
are conceptual entities, shown as names within rectangles:
Entities at the logical level represent the business in more detail than at the conceptual
level. Frequently, a conceptual entity may represent many logical entities. Logical entities
contain properties, also called “data elements” or “attributes,” which we will discuss
shortly. Entities are connected through relationships, which we will discuss shortly as well.
The figure on the next page shows the
Order
logical entities (along with their properties
and relationships) based upon the
Order
conceptual entity from above.
