Loosely Coupled Components

Abstract

Collections are widely used as a basic programming abstraction to store, retrieve and manipulate objects. There are different known types of collections (e.g., sets, bags, queues), offering various semantics for different application purposes. A collection can offer a distributed flavor, that is, it can be accessible from various nodes of a network. The elements of such a collection are thus shared between the different nodes, and a distributed collection can be viewed as a means of exchanging information between components, in a way similar to a shared memory. This chapter presents Distributed Asynchronous Collections (DACs). Roughly spoken, a DAC is capable of calling back an interested party in order to notify for instance the insertion or removal of elements. By viewing the elements of our Distributed Asynchronous Collections (DACs) as events, these collections can be seen as programming abstractions for asynchronous distributed interaction, enabling the loose coupling of components. In that sense, the DACs we present in this chapter marry the two worlds of object-orientation and event-based, so-called “message-oriented”, middleware. DACs are general enough to capture the commonalities of various message-oriented interaction styles, like message queuing and publish/subscribe interaction, and flexible enough to allow the exploitation of the differences between these styles.