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2 Proposed Architecture

 

In this section, we discuss the main components of the object-oriented framework architecture for the proposed system. A framework is a reusable, semi-complete application that can be specialized to produce custom applications [4]. It is characterized by an abstract set of classes and interfaces which, taken together, establish a generic software architecture for a family of related applications [8, ]. An interface defines an object-oriented class where all methods are abstract. Thus it supports a clear distinction between the specification of functionalities and their actual implementations.

 

figure47

Figure 1: Architecture of the application middleware  

Mainly due to the scalability issues (a large and unknown number of clients and BES) we propose a strictly decoupled multi-tier client-server architecture, as illustrated in Figure 1. A sophisticated lightweight, multithreaded application server in the middle tier loosely couples WWW clients and BES in the backend tier. Each tier is encapsulated into an uniform object-oriented interface which guarantees stable interfaces over time even for future BES which might be integrated into the system. Client and application server are connected via a message bus which serves as a standardized point-to-point communication channel within the WWW. Each client request is wrapped in a message and forwarded to the application server, which in turn is responsible for finding the appropriate application object (AO) to handle the incoming request. Each BES is encapsulated within one or a pool of dedicated application objects. Generally, aspects such as communication protocols and distribution of objects are completely hidden behind uniform framework interfaces. Thus, while guaranteeing application services at the framework level, all instances of the framework, namely all BES which are integrated into the framework, benefit from the overall infrastructure in an uniform and predictable way. Therefore, the proposed system can be seen as an application middleware for connecting BES to the WWW. The integrated BES form a loosely coupled information system.

We have adopted an object-oriented model, which is implemented in Java. However, legacy BES components do not have to be written in Java, as long as there are interfaces to glue Java and the programming language in question together, e.g. C/C++ via Java Native Interface.




next up previous
Next: 2.1 The Message Bus Up: A LightweightMessage-Oriented Application Previous: 1 Introduction

Ralf-Dieter Schimkat
Thu Dec 9 14:08:00 GMT+1 1999