IMS, IBM strategic database software using hierarchical database technology to support high-transaction volumes, provides reliable and high throughput for more than 95 percent of Fortune 1000 companies. IMS is comprised of two major components: the Database Manager (IMS DB) and Transaction Manager (IMS TM). Together, they create a complete online database transaction- processing environment, providing continuous data availability and data integrity.
IMS also provides an important interface, Open Database Access (ODBA), and protocol, Open Transaction Manager Access (OTMA). These let customers using external OS/390 or z/OS applications take advantage of the availability and integrity of IMS by providing access to IMS DB and IMS TM directly without using the traditional access methods, such as SNA.
What Is ODBA?
ODBA is a callable interface that allows for easy connection and access to IMS-managed databases. ODBA provides simplified access to IMS DB from any z/OS application address space for non- IMS applications, such as DB2 stored procedures or WebSphere application programs. Also, because sync point processing is coordinated through the use of z/OS Resource Recovery Services (RRS), you can connect to more than one IMS DB subsystem on the same z/OS image, as well as commit or back out changes with just one call.
DB2 support of ODBA allows DB2 stored procedures to access IMS data and lets DB2 coordinate sync point processing through RRS. Figure 1 presents an example of an IMS ODBA and DB2 environment.
ODBA is also easy to use; it uses the IMS Application Interface Block (AIB). The AIB lets you specify the name of the IMS Program Specification Block (PSB) that your application needs to allocate. The PSB is a control block that contains one or more descriptions of an IMS database.
In all, your application supplies the AIB, an IMS connection table that defines which IMS to connect to, the attributes of that connection, and a PSB name. With this information, the Allocate PSB (APSB) call connects you to IMS and allocates your PSB. Once connected to IMS, you need to supply only a Program Communication Block (PCB) name to make the DL/I calls used to interface with the IMS databases. The PCB describes an application program’s view of the IMS database and defines the DL/I calls the application program can use with the IMS database.
What Is OTMA?
OTMA is a transaction-based, connectionless client/server protocol specific to the IMS TM environment. OTMA uses the z/OS Cross-System Coupling Facility (XCF) to send and receive messages between the IMS OTMA clients and IMS. Using OTMA, a z/OS or TCP/IP application program can send a transaction or command to IMS without using SNA or VTAM.