10 - Data retrieval

Concepts

• Relational data model

  A data model is a language that allows the definition of:

  • the structures that will be used to store the base data;

  • the integrity constraints that the stored data have to obey at all moments in time;

  • the computer programs used to manipulate the data.

  For relational data models, the structures used to define the database are attributes, tuples, and relations. Computer programs either perform data extraction from the database without altering it, in which case they are termed queries, or they change the database contents, in which case we speak of updates or transactions.