Database Structure

A Reality database, regardless of its type, is structured in four levels:

The diagram below illustrates the four level structure of a database.

Database structure

Database Hierarchy

The three dictionary levels contain information which defines the structure of the database. Each database has one system dictionary called SYSTEM which defines all master dictionaries (MDs) below it. Each MD corresponds to an account, and defines all file dictionaries belonging to that account. Each file dictionary points to one or more data sections associated with it, one of which is generally the default data section.

Multiple index sections can exist for each data section. Each index section is closely coupled to its associated data section, being defined within the data level descriptor.

Dictionaries also contain information that defines the facilities available on the database and the format of the user data in data sections. For details, refer to the topic Dictionaries, Data Sections and Indexes.