Logical Modeling
A database is a set of data organized for use by distinct applications, to facilitate the independent evolution of the data and the application programs.
A database consists of tables, columns, keys and indexes:
• A table is the logical entity where columns are stored.
• A column is contained in a table.
• Just as an identifier uniquely identifies a class, the primary key for the table uniquely identifies a row in the table.
• A foreign key accesses another table, and imposes consistency between the corresponding columns in the tables concerned.
• An index accelerates access to data. It can be unique or not, and may be ascending or descending.