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Database design Technical implementation
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3.3.2 Defining the physical structure of a UDS/SQL database
To define the physical data structure, you use the SSL (Storage Structure Language).
The SSL is used to specify mainly:
– set information
– data placement
– optimization
– links: internal tables, chains, lists.
The data is essentially distributed over database areas via the SSL, taking the following
aspects into account:
– depending on access frequency,
– according to physical storage options (disk capacity) and
– according to the backup procedures used.
3.3.3 Views
Subschema
With the subschema DDL, the user selects sections from the database which are required
for a particular application.
For a detailed description of the subschema DDL, see page 183.
Relational schema
A relational schema is used in an SQL application. A relational schema is the relational view
of an actual subschema. Such a view can be derived from a subschema with the aid of the
utility BPSQLSIA.
For further information on the relational schema, see page 196.