Database Management System Emulation - Information Systems Reengineering, Integration and Normalization - page 227

Chapter 6
Database Management System Emulation

As database technologies evolve from hierarchical and network (nonrelational) da-
tabases to relational and object-oriented models, and as relational databases and
XML database grow in power and popularity, developers face pressure to convert
legacy databases to these newer model. In this chapter, as a part of database re-
engineering, the problem of reusing a nonrelational database system is explored.
Direct database systems conversion from nonrelational to relational is not feasible
due to the nature of reverse engineering, i.e., translating from low-level procedural
data manipulation language (DML) of a nonrelational database to an equivalent but
higher abstract level nonprocedural DML of a relational database. The approach
of adding a relational interface to a nonrelational database is preferred. The rela-
tional interface is constructed by mapping a nonrelational schema to an equivalent
relational schema. Secondary indices are added to the nonrelational schema and
database so that the relational DML does not require database navigation to access
nonrelational database. The modified schema and database can be accessed by both
nonrelational and relational database programs. Such capability can help companies
to extend the life of their nonrelational DBMSs by making them “Relational-like”
DBMSs. The nonrelational database programs can be phased out or rewritten to use
embedded SQL. After all of the nonrelational database programs are eliminated,
then, we can complete the database conversion process by converting the data of the
nonrelational database to a relational database replacing the nonrelational DBMS
(i.e., a “Relational-like” DBMS with a relational interface) by a relational DBMS.

6.1 Methodology for Adding a Relational Interface into

Nonrelational Databases

The above database conversion technique, converting a nonrelational database system
to a relational database system, is described in detail in a methodology, namely, Re-
lational-like-database, RELIKEDB, that can be summarized as follows (Fong 1993 ):