5.1 Tuple Relational Calculus Language ALPHA - Update Operations

(1) Modification Operations with UPDATE Statement

The steps to execute an update operation in ALPHA are as follows:

  1. Use the HOLD statement: Initially, retrieve the tuple to be modified from the database into the workspace using the HOLD statement.

  2. Modify attributes in workspace: Modify the attributes of the tuple in the workspace using the host language.

  3. Send modified tuple back with UPDATE: Finally, use the UPDATE statement to send the modified tuple back into the database.

Important Notes:

  • For simple data retrieval, the GET statement can be used directly.
  • However, to retrieve tuples specifically for modification, you must use the HOLD statement. This statement is a concurrent control-enabled version of GET.

Concurrency control details will be further elaborated in Chapter 5.