Effective distribution of object-oriented applications

Reviewer: Hans J. Schneider

The object-oriented paradigm adapts naturally to distributed processing. The authors present a pragmatic approach to distributing object-oriented applications over existing networks of computers. The method starts from a logical specification describing class hierarchy, object interactions, and application functionality; and a description of the network. It consists of two steps. On the intersite level, the aim is to minimize global communication, whereas optimization of several performance criteria is the primary focus on the intrasite level. First, attributes and methods of subclasses are rolled up to their farthest ancestor, creating packages containing all information relevant to every instance. Class fragments suitable as distributable units are identified by deriving appropriate predicates from scenarios. A dynamic programming model is used to allocate fragments to sites. On the intrasite level, these class fragments are broken into constituent classes, and the methods become the units of distribution. The authors distinguish among data-related models, user interface methods, and processing-related methods. The approach takes into consideration four conflicting criteria: assigning methods to the most appropriate processor type; taking advantage of concurrency; minimizing interprocessor message traffic; and considering costs of replicating object instances. The prototype tool implements an iterative and interactive procedure controlled by the designer. The concept is clearly presented, and conclusions from the discussions are summarized in brief tables. The technical details of the algorithm are not included. Interested readers are referred to technical reports on the Web.