The IMS implementation of the SQL data definition language (DDL) generally conforms to the well-defined, standard DDL syntax that is used with relational databases throughout the industry, so it makes creating and modifying IMS databases much easier for application developers and database administrators that are not familiar with IMS.

Because DDL was developed for relational databases, some of the standard DDL keywords and parameters are different than the native IMS terminology that is used to describe the physical and logical characteristics of a hierarchical database.

IMS preserves the relational terminology of the standard DDL syntax and, like most other database products, extends the syntax with IMS-specific terms when the existing, standard terminology falls short.

For example, the relational term TABLE is preserved in the IMS implementation of DDL and defines the IMS segment structure. The relation term COLUMN defines an IMS field structure.

As an example of how the IMS extends the standard DDL syntax, the IMS implementation of DDL includes a SENSEGVIEW keyword in the statements that define a program view. SENSEGVIEW corresponds to the IMS SENSEG macro instruction statement and defines the segments an application program can see.

Important: When using DDL to create program views and databases, metadata for the program views or databases is cached for the life of the JDBC JVM.

For an explanation of how relational terms map to the hierarchical structures that are used in IMS, see Comparison of hierarchical and relational databases.