Full-function database types
IMS full-function databases are hierarchical databases that are accessed through DL/I calls. IMS makes it possible for application programs to retrieve, replace, delete, and add segments to IMS databases.
IMS allows you to define twelve database types. Each type has different organization processing characteristics. Except for DEDB and MSDB, all the database types are discussed in this topic.
Understanding how the database types differ enables you to choose the type that best suits your application's processing requirements.
Each database type has its own access method. The following table shows each database type and its access method:
| Type of database | Access method |
|---|---|
| HSAM | Hierarchical Sequential Access Method |
| HISAM | Hierarchical Indexed Sequential Access Method |
| SHSAM | Simple Hierarchical Sequential Access Method |
| SHISAM | Simple Hierarchical Indexed Sequential Access Method |
| GSAM | Generalized Sequential Access Method |
| HDAM | Hierarchical Direct Access Method |
| PHDAM | Partitioned Hierarchical Direct Access Method |
| HIDAM | Hierarchical Indexed Direct Access Method |
| PHIDAM | Partitioned Hierarchical Indexed Direct Access Method |
| PSINDEX | Partitioned Secondary Index Database |
| DEDB | Data Entry Database (Hierarchical Direct Access) |
| MSDB | Main Storage Database (Hierarchical Direct Access) |
Based on the access method used, the various databases can be classified into two groups: sequential storage and direct storage.