torbjorn@chalmers.UUCP (Torbj|rn Andreasson) (06/29/87)
A while ago there was a discution of the problem of defining the term Distributed System. Unfortunately, almost every definition differed in one way or another. I think the key to the problem is to discuss principles, features and mechanisms on different abstraction levels. Why not use the existing "ISO seven layer reference model" and split the application layer in more sublayers. Why not add at least two more layers on top of the traditional ISO model, the organisation layer and the user layer. These two layers is usful when discussing principles, features and mechanisms in companies, society, etc. The following table is an approach towards some definitions, formalized in some kind of production set: -------------------------------------------------------------------------------- | Information System Architecture <-- Organisation Operational Principle, | | User Operational Principle, | | Application Operational Principle, | | Presentation Operational Principle, | | Session Operational Principle, | | Transport Operational Principle, | | Network Operational Principle, | | Link Operational Principle, | | Physical Operational Principle. | | | | Organisation Operational Principle<-- Object. | | User Operational Principle <-- Object. | | Application Operational Principle <-- Object. | | Presentation Operational Principle<-- Object. | | Session Operational Principle <-- Object. | | Transport Operational Principle <-- Object. | | Network Operational Principle <-- Object. | | Link Operational Principle <-- Object. | | Physical Operational Principle <-- Object. | | | | Object <-- <Name Scheme>, | | <Data Manipulation Primitives>, | | <Attribute Manipulation Primitives>, | | <Information Structure>, | | <Cooperation Rules>. | -------------------------------------------------------------------------------- Definition: A distributed system consists of two or more objects which have the ability to cooperate with each other. This means that from the user layer point of view, Locus is not a distributed operating system niether is NFS a distributed file system. But from the session layer level point of view, Locus and NFS are distributed systems. By using the same technique several other principles, features and mechanisms could be defined: Definition: A name transparent system is a system where all objects are accessed in the same way. Definition: A location transparent system is a system where the location of an object is not reflected in the name scheme. Definition: A ....... Definition: A ....... ........ ........ Is it someone out there who's got idea's of how to split the application layer in more usefull sublayers? ----------------------------------------------------------------------- Torbjorn Andreasson | Tel: +46 31 810100 Dept. of Computer Sciences | Telex: 2369 2369 CHALBIB S Chalmers | S-412 96 Goteborg | Sweden | UUCP: ..!mcvax!enea!chalmers!torbjorn -----------------------------------------------------------------------