IBM's DRDA paves way to interoperability; but work remains for IBM, third parties to achieve cross-platform RDBMS access - IBM's Distributed Relational Database Architecture client/server architecture for accessing remote relational data

Software Magazine, Nov, 1993 by Barbara Francett

Application requester functions support SQL and program preparation services from applications. Application server functions support requests that application requesters have sent and route requests to database servers. Most users, however, will not have to be concerned with the details of DRDA.

DRDA defines three types of data access: remote unit of work, distributed unit of work and distributed request. (See figure below.) According to IBM, a unit of work is a single logical transaction, a sequence of SQL statements.

Remote unit of work lets a user or application program read or update data at one remote location per unit of work Many SQL statements may be within a unit of work

Distributed unit of work allows a user or application to road or update data at multiple locations within a single unit of work This level adds two-phase commit, or the coordination of commit and rollback among all locations, also called coordinated recovery.

The third and most sophisticated level, distributed request, adds the ability to access many RDBMSs with each SQL statement.

All IBM products support the remote unit of work level, or DRDA1. In March, IBM announced DRDA2, the specification for the distributed unit of work level. DB2 (for MVS) is the first IBM product to support the DRDA level.

Mobil Natural Gas, Inc., located in Houston, a subsidiary of Mobil Corp., Fairfax, Va., has been working with DRDA since shortly before IBM announced it. Internal changes that paralleled the direction of DRDA had piqued the company's interest

"About four years ago, we had begun redesigning our primary line of business application, the Gas Marketing Management System [GMMS]," said Jim Parker, systems consultant. The deregulation of the gas industry in 1987 prompted the effort. Deregulation had intensified competition, lowered margins and mandated quicker responses to business changes.

"The hierarchical database system in place had become almost impossible to manage," he said. "It was hard to change or make ad hoc requests. Maintenance was costing us more than new development."

The firm brainstormed with IBM about possible relational strategies. It decided on a relational, client/server environment based on IBM's Systems Application Architecture (SAA). "We started developing internally with OS/2 Extended Edition and its database manager," Parker said. "Our goal was to be able to migrate to the mainframe database world, AS/400 or whatever platform we might need."

However, Parker said it soon became obvious that IBM's DRDA product would be completed before the internal development effort. "IBM kept saying that their solution would work for us," said Parker. When IBM announced DRDA in late 1990, Mobil Natural Gas received and began working with an early shipment of code for SQL/DS and DDCS/2.

The company called the new, relational version of GMMS Gamma, which works with virtually every aspect of gas marketing. This includes purchasing and selling, shipping, and contractual and accounting issues. It runs in a client/server environment.