Data dictionary

A data dictionary is a catalog that provides information about the data in a database. It can be thought of as “data about the data,” or metadata. A data dictionary can be used to describe data that resides within a database table.

LN maintains a data dictionary because the data that LN applications use must be described in a database-independent manner. LN domains and data types can differ from those available in the database server. The database driver performs any mapping and translation required to store and retrieve the LN data in the database server. The LN data dictionary defines LN data types, domains, schemas, and referential integrity information. The database driver maps this information to the appropriate elements in the RDBMS. When storing or retrieving data in the RDBMS, the database driver maps data dictionary information to database table definitions.

LN data dictionary information can be cached in shared memory where it is available to all running LN application virtual machines. The data dictionary information is shared among all the sessions open within a single database driver.

The LN data types cannot be used directly by the database driver to create RDBMS tables. This is because not all LN data types exactly match the RDBMS data types. To create valid tables, the driver must perform some mapping or translation. When mapping the LN data dictionary to tables in the specific RDMS, conventions are used for the table names, column names, and index names.