Final answer:
In the relational model, keys are crucial as they ensure the unique identification of each row in a table. Various keys like primary keys, foreign keys, candidate keys, and composite keys have different functions for data integrity and relational links.
Step-by-step explanation:
A key, or index, as the term itself indicates, unlocks access to the tables. If you know the key, you know how to identify specific records and the relationships between the tables. Each key consists of one or more fields, or field prefix. In the relational model, keys are important because they are used to ensure that each row in a table is uniquely identifiable. A key can be a single attribute or a combination of multiple attributes that uniquely identifies a tuple (row) in a relation (table). Keys play a critical role in the integrity and efficiency of the database system.
There are different types of keys in relational databases: Primary keys - A set of one or more attributes that, taken collectively, uniquely identify a record in the table. No two records can have the same value for the primary key. Foreign keys - Used to establish a link between the data in two tables. It acts as a cross-reference between tables as it references the primary key of another table. Candidate keys - Any column, or set of columns, that could qualify as a unique key in a table. Composite keys - A combination of two or more columns in a table that can be used to uniquely identify each row in the table. Understanding these keys is vital for anyone involved in database design, management, or data integrity.