Final answer:
In the relational model, a constraint is used to define limitations on what the data can be in tables to ensure data integrity. Constraints can define domain integrity, entity integrity, and referential integrity within the database.
Step-by-step explanation:
A constraint in the relational model is a rule that is used to define limitations on the data that can be stored in tables. These constraints ensure the integrity and correctness of the data within the database. In the context of the relational data model, constraints can enforce various restrictions, such as:
- Domain constraints, which define the allowable values for a given attribute or column within a table.
- Referential integrity constraints, which ensure that relationships between tables remain consistent.
- Entity integrity constraints, which ensure that each entity (row) is uniquely identifiable.
It is important to differentiate between constraints and criteria when discussing database design. While constraints indicate the mandatory conditions that must be fulfilled, criteria are attributes that help to evaluate and compare different designs or solutions. Both elements play crucial roles in the database design and evaluation process.