Determining key group attributes is an important task in developing a logical model. A key group is a logical modeling tool that you use to identify:
- Relationships between entities, that are implemented as foreign keys. A foreign key appears in a child entity and represents the migration of the primary key of the parent entity to the child entity.
- Potential primary keys or alternate keys for use in the physical model. Primary and alternate keys are unique keys created from one or more attributes that uniquely identify a single instance in an entity. For example, unique keys in the customer entity may include customer number, social security number, or first and last name plus telephone number.
- The most efficient primary or alternate keys. From the list of available unique keys, you can select the primary key or the alternate key that most efficiently accesses database information. You can, for example, create a surrogate key, such as customer number, to increase database access efficiency.
- Potential inversion entry keys in the logical model. An inversion entry key comprises one or more attributes that are frequently used to access information in the entity, but are non-unique. An example of a useful inversion entry is customer last name. Although you may have many customers with the same last name, it is useful to look up information for a customer using their last name instead of their customer number.
You can define primary keys, alternate keys, foreign keys, and inversion entries in your logical model. Any or all the keys from a logical model can subsequently appear as indexes for the corresponding tables in the physical model.
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