The system dictionary is a table, called Dictionary Entry [sys_dictionary], that contains details for each table and the definition for every column on each table in an instance.

Each row in the system dictionary represents either a table or a column in one of the tables. The system dictionary provides options for administrators to modify tables and fields, which in turn define lists and forms.

Use caution when changing system dictionary records because changes can have a high impact on functionality. In particular, changes to dictionary entries for system tables, which are tables that begin with sys_, can create system-wide issues such as the inability to use update sets.

Dictionary changes are difficult to reverse. Also, dictionary changes automatically apply to all extended tables unless a dictionary override is defined. Be sure that changes are well-tested before applying them to a production instance.