Automatic generation of programs for retrieving information from CODASYL databases
In recent years, a substantial investment has been made in data base management systems which are based on the proposals of various CODASYL committees. These systems are typically capable of storing large volumes of data through the use of sophisticated data structures but incur a cost in terms of complex access methods and program development time.Recent research in relational data base management systems has led to the development of data manipulation techniques with ease of use as the principal consideration. This thesis addresses the problem of providing a relational query interface to CODASYL data base management systems and demonstrates that reasonable access strategies can be deduced for queries expressed in an extended form of relational algebra.Topics discussed include general considerations in the provision of a query view for users who are not computer professionals, the design of a suitable query language, novel methods of query validation -and result layout description using interactive simulators and the derivation of relational views of CODASYL schemes. A powerful method of data base access path description based on the notion of a "traversal" is introduced. Traversals are easily modified to include relational algebra operations and a straightforward algorithm for generating code from them is described. Finally, the results of a small evaluation experiment are presented as a justification of this technique for implementing relational algebra expressions.