The Transition of Application Programs From COBOL to a Fourth Generation Language

It is becoming increasingly desirable to move older application programs from their traditional mainframe execution environments to networked workstations. These management information systems are most often written in COBOL and store their data in les. A networked environment enables the use of a relational database management system and its fourth generation access language, SQL. A conceptual framework is described that comprises a variety of strategies for making such a transition. Decision criteria for selecting among them are then presented. Finally, a variety of experiments intended to explore the strategies are recounted. The experiments include eeorts to automate parts of the process. The advantages of moving existing COBOL main-frame management information systems to a fourth generation language (4GL) environment based on a re-lational database management system (RDBMS) are both economic and technical. Distributed access. The data and procedures provided by an RDBMS application are available to other programs and people. The programs and people may be geographically distributed. Transportability. An RDBMS typically supports the standard database query language, SQL. This enhances vendor and platform independence , thereby increasing exibility. Database features. An RDBMS supports a variety of services that are not likely to be available in a standalone application program. Typical features include security, data integrity, rollback and crash recovery, and locking. Increased abstractness. Many application features present in COBOL programs can be described declaratively or avoided altogether when using a 4GL. For example, an RDBMS requires explicit models of the data it contains. Some of this information is available as le descriptions in the COBOL code, but it is often very concrete , and more conceptual aspects of the data are present only implicitly in the procedural code. Moreover, once data have been moved from les into databases, enterprise-wide data integration can be addressed. An RDBMS also provides a variety of functions that have to be coded explicitly in a COBOL program. For example, a forms-based, data entry tool can replace much data entry and validation code. Likewise, a report generator can replace code that explicitly formats output reports, and query operations can replace complex procedural code. Improved maintainability. Estimates indicate that several hundred billion lines of source code exist in the world and that seventy percent of it is written in COBOLL20]. The largest cost factor in software development is maintaining existing programs after they are delivered. Up to 75% of life cycle cost may be expended on such …