These are the basic functions used to open and close a data dictionary. In the sense that a data dictionary contains information about the tables that are available, the data dictionary defines the database. Also the permission function is included here.
The typical sequence of usage would be to try opening the data dictionary, set the permissions, use the table and row level calls, and then close the data dictionary.
When ddopen() is called the locking mechanisms are also put into place. A call to ddclose() must be made to remove these mechanisms, otherwise it is possible that there will be a wastage of some system resources. The nature of this wastage will depend on the operating system in use, and the manner in which locks are maintained.