DDL SQL

IMS supports and extends the SQL data definition language (DDL).

IMS databases use a hierarchical database structure. The standard SQL DDL statements use parameters, keywords, and concepts that are based on relational database structures. While it is not always necessary to understand the hierarchical structure and associated concepts of IMS databases when creating or altering IMS databases with DDL, such an understanding will likely help you define IMS database structures that are more efficient and perform better. For more information about how relational database terms and concepts map to the hierarchical structures of IMS, see Comparison of hierarchical and relational databases.