Findings of a comparison of five filing protocols

Filing protocols are essential for the management and dissemination of shared information within computer systems. This is a survey of the current state of the art in filing protocols. Five popular filing protocols were selected and subjected to a rigorous comparison. FTAM, FTP, UNIX rep, XNS Filing, and NFS are compared in the following areas: exported interface, concurrency control, access control, error recovery, and performance. The coverage of background material includes a taxonomy and a brief history of filing protocols

Office automation

Bibliography: p. 100-104.Office automation systems have become an essential tool for the operation of the modern office. With the emphasis of a modern office being placed on efficiency and ease of communication, office automation systems have become the backbone of successful businesses. COSNET is a prototype office automation system designed and implemented at the Department of the University of Cape Town and runs on Personal Computers that are linked to a NCR UNIX TOWER, which acts as the host. This dissertation investigates the different facilities supported by some of the office automation systems compared in this thesis, and describes the COSNET features. This prototype office automation system supports many of the facilities that are supported by large office automation systems. COSNET allows the user to define any MS-DOS based editor or word processor, and uses a simple editor for the creation of mail. The electronic filing facility allows documents to be created, filed, retrieved and deleted, and thus provides the users with the necessary features for document exchange. A user may set access permissions to each of his documents and may grant other users either read or write access to a specific document. The mail facility lets the user read, file, forward, delete and print a message, and supports classification of mail. A calendar facility is used as an electronic diary and stores all the user's schedules. These schedules may be viewed in either daily, weekly and monthly display modes. Read and write access to the calendar can be set by the user, in order to allow other users to manipulate his schedules. Any MS-DOS based application software can be added to COSNET. This facility allows the COSNET user to configure the office automation system to simulate the office environment. COSNET thus supports most of the necessary features required by an office automation system

Software product description

An overview of the MultiNet system is presented. Services, supported configurations, remote printer services, netstat, netcontrol, DECnet interoperability services, and programming libraries are briefly described

Formalizing a hierarchical file system

An abstract file system is defined here as a partial function from (absolute) paths to data. Such a file system determines the set of valid paths. It allows the file system to be read and written at a valid path, and it allows the system to be modified by the Unix operations for creation, removal, and moving of files and directories. We present abstract definitions (axioms) for these operations. This specification is refined towards a pointer implementation. The challenge is to have a natural abstraction function from the implementation to the specification, to define operations on the concrete store that behave exactly in the same way as the corresponding functions on the abstract store, and to prove these facts. To mitigate the problems attached to partial functions, we do this in two steps: first a refinement towards a pointer implementation with total functions, followed by one that allows partial functions. These two refinements are proved correct by means of a number of invariants. Indeed, the insights gained consist, on the one hand, of the invariants of the pointer implementation that are needed for the refinement functions, and on the other hand of the precise enabling conditions of the operations on the different levels of abstraction. Each of the three specification levels is enriched with a permission system for reading, writing, or executing, and the refinement relations between these permission systems are explored. Files and directories are distinguished from the outset, but this rarely affects our part of the specifications. All results have been verified with the proof assistant PVS, in particular, that the invariants are preserved by the operations, and that, where the invariants hold, the operations commute with the refinement functions

Formalizing a hierarchical file system

An abstract file system is defined here as a partial function from (absolute) paths to data. Such a file system determines the set of valid paths. It allows the file system to be read and written at a valid path, and it allows the system to be modified by the Unix operations for creation, removal, and moving of files and directories. We present abstract definitions (axioms) for these operations. This specification is refined towards a pointer implementation. The challenge is to have a natural abstraction function from the implementation to the specification, to define operations on the concrete store that behave exactly in the same way as the corresponding functions on the abstract store, and to prove these facts. To mitigate the problems attached to partial functions, we do this in two steps: first a refinement towards a pointer implementation with total functions, followed by one that allows partial functions. These two refinements are proved correct by means of a number of invariants. Indeed, the insights gained consist, on the one hand, of the invariants of the pointer implementation that are needed for the refinement functions, and on the other hand of the precise enabling conditions of the operations on the different levels of abstraction. Each of the three specification levels is enriched with a permission system for reading, writing, or executing, and the refinement relations between these permission systems are explored. Files and directories are distinguished from the outset, but this rarely affects our part of the specifications. All results have been verified with the proof assistant PVS, in particular, that the invariants are preserved by the operations, and that, where the invariants hold, the operations commute with the refinement functions

Second CLIPS Conference Proceedings, volume 1

Topics covered at the 2nd CLIPS Conference held at the Johnson Space Center, September 23-25, 1991 are given. Topics include rule groupings, fault detection using expert systems, decision making using expert systems, knowledge representation, computer aided design and debugging expert systems