Data Storage
Field interface definitions, as defined in the Database Interface property, determine how data is stored in a specific DBMS storage format, and how Uniface deals with the data when it is retrieved. The definitions specify the Uniface data type and packing code, which are mapped by the DBMS connector to the DBMS data type, known as a storage format.
Uniface Record Structure
Uniface imposes a maximum number of 256 fields per entity.
The Uniface entity can be split into:
- A fixed-length part that contains all fixed-length fields. The maximum size
of the fixed-length part of a record is 32KB.
Most DBMSs require fixed-length indexed fields, so all index and key fields must be defined in the fixed-length part of the entity. The maximum size of each index or primary key is 500 bytes.
- A variable-length part that contains all
variable-length fields, if any are defined in the entity. A
variable-length part is also created when the entity contains an included entity.
All variable-length fields must be added to the end of the entity.
Variable Length Fields
For most DBMSs, the variable portion is simply a single long field. If not supported by the underlying DBMS, Uniface maps variable-length fields and included entities into this field in the format defined in the modeled entity.
You can define variable-length fields and included entities in the variable-length portion of a record by using the Database Interface property of modeled entities and their fields.
Caution: Using these variable length definitions can severely reduce the accessibility of your data by other programs, if your DBMS does not support these techniques.
