分布式计算原理与应用(DistributedComputing)第三章课件.ppt

Distributed Computing Paradigms, M. Liu Distributed Computing Paradigms Mei-Ling Liu Paradigms for Distributed Applications Paradigm means “a pattern, example, or model.” In the study of any subject of great complexity, it is useful to identify the basic patterns or models, and classify the detail according to these models. This paper aims to present a classification of the paradigms for distributed applications. Characteristics that distinguish distributed applications from conventional applications which run on a single machine. These characteristics are: Interprocess communication: A distributed application require the participation of two or more independent entities (processes). To do so, the processes must have the ability to exchange data among themselves. Event synchronization: In a distributed application, the sending and receiving of data among the participants of a distributed application must be synchronized. Abstractions Arguably the most fundamental concept in computer science, abstraction is the idea of detail hiding. To quote David J. Barnes1: We often use abstraction when it is not necessary to know the exact details of how something works or is represented, because we can still make use of it in its simplified form. Getting involved with the detail often tends to obscure what we are trying to understand, rather than illuminate it … Abstraction plays a very important role in programming because we often want to model, in software, simplified versions of things that exist in the real world … without having to build the real things. In software engineering, abstraction is realized with the provision of tools or facilities which allow software to be built without the developer having to be cognizant of some of the underlying complexities. Distributed Application Paradigms The Message Passing Paradigm Message passing is the most fundamental paradigm for distributed applications. A process sends a message representing a request.