Making Ontologies Work For Resolving Redundancies Across Documents
Producing normalized representations from different ways of expressing the same idea.
Daniel G. Bobrow
Advertisement
Author Archives
CLOS: integrating object-oriented and functional programming
Lisp has a long history as a functional language,* where action is invoked by calling a procedure, and where procedural abstraction and encapsulation provide convenient modularity boundaries. A number of attempts have been made to graft object-oriented programming into this framework without losing the essential character of Lisp—to include the benefits of data abstraction, extensible type classification, incremental operator definition, and code reuse through an inheritance hierarchy.
The Common Lisp Object System (CLOS) [3], a result of the ANSI standardization process for Common Lisp, represents a marriage of these two traditions. This article explores the landscape in which the major object-oriented facilities exist, showing how the CLOS solution is effective within the two contexts.
Beyond the chalkboard: computer support for collaboration and problem solving in meetings
Although individual use of computers is fairly widespread, in meetings we tend to leave them behind. At Xerox PARC, an experimental meeting room called the Colab has been created to study computer support of collaborative problem solving in face-to-face meetings. The long-term goal is to understand how to build computer tools to make meetings more effective.
An efficient, incremental, automatic garbage collector
This paper describes a new way of solving the storage reclamation problem for a system such as Lisp that allocates storage automatically from a heap, and does not require the programmer to give any indication that particular items are no longer useful or accessible. A reference count scheme for reclaiming non-self-referential structures, and a linearizing, compacting, copying scheme to reorganize all storage at the users discretion are proposed. The algorithms are designed to work well in systems which use multiple levels of storage, and large virtual address space. They depend on the fact that most cells are referenced exactly once, and that reference counts need only be accurate when storage is about to be reclaimed. A transaction file stores changes to reference counts, and a multiple reference table stores the count for items which are referenced more than once.
In current machine designs, a machine address gives the user direct access to a single piece of information, namely the contents of that machine word. This note is based on the observation that it is often useful to associate additional information, with some (relatively few) address locations determined at run time, without the necessity of preallocating the storage at all possible such addresses. That is, it can be useful to have an effective extra bit, field, or address in some words without every word having to contain a bit (or bits) to mark this as a special case. The key idea is that this extra associated information can be found by a table search. Although it could be found by any search technique (e.g. linear, binary sorted, etc.), we suggest that an appropriate low overhead mechanism is to use hash search on a table in which the key is the address of the cell to be augmented.
A model and stack implementation of multiple environments
Many control and access environment structures require that storage for a procedure activation exist at times when control is not nested within the procedure activated. This is straightforward to implement by dynamic storage allocation with linked blocks for each activation, but rather expensive in both time and space. This paper presents an implementation technique using a single stack to hold procedure activation storage which allows retention of that storage for durations not necessarily tied to control flow. The technique has the property that, in the simple case, it runs identically to the usual automatic stack allocation and deallocation procedure. Applications of this technique to multitasking, coroutines, backtracking, label-valued variables, and functional arguments are discussed. In the initial model, a single real processor is assumed, and the implementation assumes multiple-processes coordinate by passing control explicitly to one another. A multiprocessor implementation requires only a few changes to the basic technique, as described.
Requirements for advanced programming systems for list processing
List processing systems should be designed to facilitate production of large programs to manipulate large complex symbolic data stores. This paper presents an overview of a number of system features which the author feels are important to improve the productivity of programmers working in such domains. A systems view is taken, rather than focusing just on language features, since algorithms must be not only coded in a language form, but debugged, modified, made efficient, and run on data. Because of this general framework, the requirements specified are applicable to the design of advanced programming systems for a wide range of applications.
Three aspects of programming systems are highlighted: good interactive facilities, programmable control structures, and sophisticated data communication mechanisms. Interactive features are described to facilitate program composition, entry, testing, debugging, editing, optimization, and packaging. Implementation of a generalized environment structure model specified would allow programming of various control regimes including multiprocesses, coroutines and backtracking. Alternative methods of procedure invocation required include invocation by pattern and by monitoring condition. The need for extended data forms, storage management, and extensibility are stressed, as is the duality of data retrieval and function evaluation. Syntax directed input and output of data would facilitate use of complex data stores.
TENEX, a paged time sharing system for the PDP – 10
TENEX is a new time sharing system implemented on a DEC PDP-10 augmented by special paging hardware developed at BBN. This report specifies a set of goals which are important for any time sharing system. It describes how the TENEX design and implementation achieve these goals. These include specifications for a powerful multiprocess large memory virtual machine, intimate terminal interaction, comprehensive uniform file and I/O capabilities, and clean flexible system structure. Although the implementation described here required some compromise to achieve a system operational within six months of hardware checkout, TENEX has met its major goals and provided reliable service at several sites and through the ARPA network.
Theoretical and practical values of error coefficients useful in bounding the error in integrating periodic analytic functions with the trapezoidal rule are tabulated for various ranges of the parameters.
A note on the efficiency of a LISP computation in a paged machine
The problem of the use of two levels of storage for programs is explored in the context of a LISP system which uses core memory as a buffer for a large virtual memory stored on a drum. Details of timing are given for one particular problem.
Shape the Future of Computing
ACM encourages its members to take a direct hand in shaping the future of the association. There are more ways than ever to get involved.
Get Involved