Patterns for Layered Object-Oriented Applications

Three-layered architectures (presentation, business and persistence levels) are sometimes recommended when developing object-oriented applications. Using the increasingly popular fourth generation languages, however, layering is difficult: business rules are usually embedded in user interfaces, which may also directly access databases. In this paper, we present three patterns useful in the construction of object oriented applications accessing relational databases via fourth generation languages. Motivation With the increasing interest in object-oriented technology, many companies have started to worry about how to store application business objects in databases. A natural approach to store objects would be to use an object-oriented database system. However, in practice, many companies have instead opted to use a relational database to store objects [Duhl96], as witnessed by the increasing popularity of Fourth Generation Languages (4GL's), such as Powerbuilder and Delphi. By combinin..