When an attribute, or field, of a table or file may have multiple values. For example, in a COBOL sequential file, its corresponding record may have a field, A, with several allowable values (Y, N, D). Translating this multivalued attribute to its relational database equivalent model is difficult; hence, lists or linked tables containing the possible values of this attribute are used in order to represent it in the relational model.
Published in Chapter:
Data Reengineering of Legacy Systems
Richard C. Millham (Catholic University of Ghana, Ghana)
Copyright: © 2009
|Pages: 8
DOI: 10.4018/978-1-60566-242-8.ch005
Abstract
Legacy systems, from a data-centric view, could be defined as old, business-critical, and standalone systems that have been built around legacy databases, such as IMS or CODASYL, or legacy database management systems, such as ISAM (Brodie & Stonebraker, 1995). Because of the huge scope of legacy systems in the business world (it is estimated that there are 100 billion lines of COBOL code alone for legacy business systems; Bianchi, 2000), data reengineering, along with its related step of program reengineering, of legacy systems and their data constitute a significant part of the software reengineering market. Data reengineering of legacy systems focuses on two parts. The first step involves recognizing the data structures and semantics followed by the second step where the data are converted to the new or converted system. Usually, the second step involves substantial changes not only to the data structures but to the data values of the legacy data themselves (Aebi & Largo, 1994).