The Development Of Digital Library Using AO

Using modern software development methodology, developers first decompose system into small units, which hide the internal implementation and provide only external interfaces, then implement these units, at last compose these units to get a full system and realize required functions .But there are some non-functional concerns which crosscut whole system and can't be well encapsulated into a single module. These aspects are scattered and tangled in whole system, decreasing software traceability, reusability, adaptability. So these non-functional concerns should be separated and modularized.The Aspect-Oriented paradigm builds on the existing Object Oriented paradigm by introducing the notion of an aspect as opposed to a core class. The AOP separates and modularizes crosscutting concerns at implementation stage. Using this technique, aspects are placed in separate modules that are then woven together with base classes to form an application. The AOP makes the implementation of the crosscutting concerns of the system more modularized ,and more easy to implement the evolvement of the system.It is unnecessary to consider the crosscutting concerns of the system when we design the function component of the system. Consequently it increases the traceability, reusability and adaptability of software .Aspect-Oriented Modeling (AOM) specifies, visualizes, constructs and documents aspect related artifacts in a consistent way at other stage of software development. Thus whole software development process can use aspect-oriented technique.The digital library is a so complex system with many non-functional concerns , such as logging, performance analysis, security, contextrelated error handling, QoS monitoring, etc(always scatter in the whole system) . So the it is very difficulty to guarantee the efficiency and quality of the software with traditionary methods of systems analysis and design . In order to design more logical system, accelerate development process, improve quality of software, we adopt the Aspect-Oriented software development .It also makes it more convenient to integrate resource of these existing digital library, and alleviates the complication of digital library's development . Otherwise with AOP to build system is favourable to satisfy the increasing extending requirement of the digital library.This article presents the theory of AOP, and particularly analyze the AspectJ;summarizes the researches in AOM domain;analyses the primary crosscutting concerns in the digital library. This article proposes a new technique to modeling aspect-oriented constructs and mechanisms by extending UML, which can represent constructs and weaving mechanism of AspectJ with appropriate semantics. In this method, aspect is subclass of class;pointcut and joinpoint is association relationship, advice is denoted by operation;introduction derived from feature. The article also examines how this technique can be practiced in digital library systems development.