Combining contracts and exemplar-based programming for class hiding and customization

Abstract

For performance reasons, client applications often need to influence the implementation strategies of libraries whose services they use. If an object-oriented library contains multiple service classes customized for different usage patterns, applications can influence service implementations by instantiating the customized classes that match their needs. However, with many similar service classes, it can be difficult for applications to determine which classes to instantiate. Choosing the wrong class can result in very subtle errors since a customized class might use optimizations that work only over a restricted domain. In this paper, we show how client-side software contracts and exemplar-based class factories can be used to construct customized server objects. By expressing priorities and requirements in contracts, clients can delegate service class selection to the library and thereby avoid implicit dependencies on the library implementation. We have used this approach in the implementation of a real-time database system.

Architectural support for quality of service for CORBA objects

“…A programmer can extend the behavior of the language by providing his own meta-classes. The MOP approach is now being applied in more general contexts (Kiczales & Lamping 1993Masahura et al 1995Kiczales et al 1991;Kiczales 1994;Anderson 1995a;Anderson 1995b;Lortz et al 1994).…”

Open implementation analysis and design

“…Rather, the concept is that a single module, often created with an existing programming language, cart support multiple clients. For example, Lortz and Shin describe how Open Implementations may be used to create customized server objects in a real-time database system in C++ [LS94]. In their approach, Interfaces to an Open Implementation clients can express the properties and behavior they desired from a server as a string parameter passed to a server factory:2 MdartsArray<int> parts_list ("par ts_list", range checked; sparse; "persistent; _ size=1000") ;…”

“…The designers and builders of an 01 must take the client's perspective and determine: 2 This example is from Lortz and Shin~. 457,LS94]. q the facets of client behavior that are relevant to the 01 module, q means of determining those facets of client behavior, q the strategies to be implemented in the 01 module, and q a means of selecting a strategy for a particular client behavior profile.…”