ppxscal/embedding_network huggingface dataset:
Modal nonmonotonic logics: ranges, characterization, computation
Authors: V. Wiktor Marek, Grigori F. Schwarz, Mirosław Truszczyński
Venue: Journal of the ACM (JACM) (1993)

Many nonmonotonic formalism, including default logic, logic programming with stable models, and autoepistemic logic, can be represented faithfully by means of modal nonmonotonic logics in the family proposed by McDermott and Doyle. In this paper properties of logics in this family are thoroughly investigated. We present several results on characterization of expansions. These results are applicable to a wide class of nonmonotonic modal logics. Using these characterization results, algorithms for computing expansions for finite theories are developed. Perhaps the most important finding of this paper is that the structure of the family of modal nonmonotonic logics is much simpler than that of the family of underlying modal (monotonic) logics. Namely, it is often the case that different monotonic modal logics collapse to the same nonmonotonic system. We exhibit four families of logics whose nonmonotonic variants coincide: 5-KD45, TW5-SW5, N-WK, and W5-D4WB. These nonmonotonic logics naturally represent logics related to commonsense reasoning and knowledge representation such as autoepistemic logic, reflexive autoepistemic logic, default logic, and truth maintenance with negation.
The object-oriented paradigm in the undergraduate curriculum: a survey of implementations and issues
Authors: Dorothy Mazaitis
Venue: ACM SIGCSE Bulletin (1993)

Many undergraduate computer science programs have not yet incorporated the object-oriented paradigm into their curriculum or have done so only minimally. Furthermore, programs which do teach object-oriented design and programming do so in a variety of ways. This paper presents a survey of different approaches to incorporating the object-oriented paradigm into the undergraduate curriculum. Data were complied from experiences related in the current literature and from a survey of undergraduate programs in Connecticut. To round out the discussion, feedback from local industry with regard to its use of this methodology is included: specifically, is there a need for proficiency in object-oriented design and programming?
Improved parallel I/O via a two-phase run-time access strategy
Authors: Juan Miguel del Rosario, Rajesh Bordawekar, Alok Choudhary
Venue: ACM SIGARCH Computer Architecture News (1993)

As scientists expand their models to describe physical phenomena of increasingly large extent, I/O becomes crucial and a system with limited I/O capacity can severely constrain the performance of the entire program.We provide experimental results, performed on an lntel Touchtone Delta and nCUBE 2 I/O system, to show that the performance of existing parallel I/O systems can vary by several orders of magnitude as a function of the data access pattern of the parallel program. We then propose a two-phase access strategy, to be implemented in a runtime system, in which the data distribution on computational nodes is decoupled from storage distribution. Our experimental results show that performance improvements of several orders of magnitude over direct access based data distribution methods can be obtained, and that performance for most data access patterns can be improved to within a factor of 2 of the best performance. Further, the cost of redistribution is a very small fraction of the overall access cost.
A tour advisory system using a logic programming approach
Authors: Panagiotis Stamatopoulos, Isambo Karali, Constantin Halatsis
Venue: ACM SIGAPP Applied Computing Review (1993)

A PErsonalized Tourist INformation Advisor is presented, called PETINA, which is a system aiming at constructing tours that satisfy constraints specified by tourists. The system consults a database which contains information about activities, events and sites that refer to Greece. PETINA takes as input user wishes about tour generation expressed as constraints over visits' properties and its output is tours satisfying these constraints. The user wishes may be stated using either a formal language or a graphical interface. The method of computation applies to any problem domain, in case the problem involves combinatorial searching under some kinds of constraints that can be classified into some well defined categories. Although a logic programming approach is suitable and valuable for the formulation of combinatorial search problems, conventional Prolog systems fail to cope with them efficiently. PETINA has been implemented in the ElipSys language, which is a parallel logic programming system extended with various porwerful mechanisms to allow efficient execution. Most of the ElipSys' features were proved to be indispensable for handling the complexity of the encountered problems.
Efficient decision procedures for graph properties on context-free graph languages
Authors: Thomas Lengauer, Egon Wanke
Venue: Journal of the ACM (JACM) (1993)

Efficient ways of analyzing families of graphs that are generated by a certain type of context-free graph grammars are considered. These graph grammars are called cellular graph grammars. They generate the same graph families as hyperedge replacement systems, but are defined in a way that supports complexity analysis. A characteristic called &ldquo;finiteness&rdquo; of graph properties are defined, and combinatorial algorithms are presented for deciding whether a graph language generated by a given cellular graph grammar contains a graph with a given finite graph property. Structural parameters are introduced that bound the complexity of the decision procedure and special cases for which the decision can be made in polynomial time are discussed. Extensions to graph grammars that are not context-free are also given. Our results provide explicit and efficient combinatorial algorithms where, so far, only the existence of algorithms has been shown, or the best known algorithms are highly inefficient.
Using icons to find documents: simplicity is critical
Authors: Michael D. Byrne
Venue: Proceedings of the INTERACT '93 and CHI '93 conference on Human factors in computing systems (1993)

A common task at almost any computer interface is that of searching for documents, which GUIs typically represent with icons. Oddly, little research has been done on the processes underlying icon search. This paper outlines the factors involved in icon search and proposes a model of the process. An experiment was conducted which suggests that the proposed model is sound, and that the most important factor in searching for files is the type of icons used. In general, simple icons (those discriminable based on a few features) seem to help users, while complex icons are no better than simple rectangles.
Discrete-event simulation and the event horizon
Authors: Jeff S. Steinman
Venue: ACM SIGSIM Simulation Digest (1994)

The event horizon is a very important concept that is useful for both parallel and sequential discrete-event simulations. By exploiting the event horizon, parallel simulations can process events in a manner that is risk-free (i.e., no antimessages) in adaptable &ldquo;breathing&rdquo; time cycles with variable time widths. Additionally, exploiting the event horizon can greatly reduce the event list management overhead that is common to virtually all discrete-event simulations. This paper develops an analytic model describing the event horizon from first principles using equilibrium considerations and the hold model (where each event, when consumed, generates a single new event with future-time statistics described by a known probability function). Exponential and Beta-density functions are used to verify the mathematics presented in this paper.
Library for architecture-independent development of structured grid applications
Authors: Max Lemke, Daniel Quinlan
Venue: ACM SIGPLAN Notices (1993)

P++ is an innovative user environment that simplifies the development of efficient, parallel programs for large scale scientific applications. It permits portability across the widest variety of computer architectures. The target machines are distributed memory computers with different types of node architectures (scalar, vector, or superscalar), but the requirements of shared memory computers are also addressed. Unfortunately, robust, architecture-independent and efficient software environments have been notable to date primarily by their absence. Such a simplifying environment for the development of software is sorely needed to take advantage of the current and future developments in advanced computational hardware. The P++ environment does this using a standard language, C++, with absolutely no modification of the compiler. For parallel communication it employs existing widely portable communications libraries. Such an environment allows existing C++ language compilers to be used to develop software in the preferred serial environment, and such software to be efficiently run, unchanged, in all target environments.The explicit goal of P++ is the support of advanced computational methods for the solution of large-scale computational problems. For efficiency reasons and also for simplification, the use of P++ is restricted to the large class of structured grid methods for partial differential equations. Applications using P++ can selectively exploit the added degree of freedom presented by parallel processing by use of an optimization module within the array language interface. A collection of defaults ensures deterministic behavior. In this way, complicated optimization issues of parallel execution may be easily introduced by the setting of switches within the user interface, which are then interpreted at runtime. Through the use of Virtual Shared Memory, restricted to array variables (Virtual Shared Grids), issues such as partitioning become matters of optimization, and not criteria for correct execution. Due to the restriction and optimization for structured grids, we expect the same parallel performance as for codes based on the traditionally used explicit Message Passing model. To speed the development of the P++ environment, we use an efficient, commercially available array language library, M++, developed in C++; the M++ array interface is also used as the P++ array interface.Recognizing that the acceptance of advanced parallel computers depends on their use by scientists, and not parallel researchers, it is hoped that P++ will simplify access to these parallel machines. While significantly simplifying our own research on parallel self adaptive local refinement methods, it is hoped that P++ will more generally simplify the introduction of structured grid methods for large scale scientific computing onto advanced parallel machines.
Content awareness in a file system interface: implementing the &ldquo;pile&rdquo; metaphor for organizing information
Authors: Daniel E. Rose, Richard Mander, Tim Oren, Dulce B. Poncéleon, Gitt Salomon, Yin Yin Wong
Venue: Proceedings of the 16th annual international ACM SIGIR conference on Research and development in information retrieval (1993)

The pile is a new element of the desktop user interface metaphor, designed to support the casual organization of documents. An interface design based on the pile concept suggested uses of content awareness for describing, organizing, and filing textual documents. We describe a prototype implementation of these capabilities, and give a detailed example of how they might appear to the user. We believe the system demonstrates how content awareness can be not only used in a computer filing system, but made an integral part of the user's experience.
Dependence-based program analysis
Authors: Richard Johnson, Keshav Pingali
Venue: Proceedings of the ACM SIGPLAN 1993 conference on Programming language design and implementation (1993)

Program analysis and optimization can be speeded up through the use of the dependence flow graph (DFG), a representation of program dependences which generalizes def-use chains and static single assignment (SSA) form. In this paper, we give a simple graph-theoretic description of the DFG and show how the DFG for a program can be constructed in O(EV) time. We then show how forward and backward dataflow analyses can be performed efficiently on the DFG, using constant propagation and elimination of partial redundancies as examples. These analyses can be framed as solutions of dataflow equations in the DFG. Our construction algorithm is of independent interest because it can be used to construct a program's control dependence graph in O(E) time and its SSA representation in O(EV) time, which are improvements over existing algorithms.
The development of the C language
Authors: Dennis M. Ritchie
Venue: ACM SIGPLAN Notices (1993)

The C programming language was devised in the early 1970s as a system implementation language for the nascent Unix operating system. Derived from the typeless language BCPL, it evolved a type structure; created on a tiny machine as a tool to improve a meager programming environment, it has become one of the dominant languages of today. This paper studies its evolution.
Denial of service
Authors: Roger M. Needham
Venue: Proceedings of the 1st ACM conference on Computer and communications security (1993)

The contractor uses the client, the network, and the server to give a service to the customer. We put it this way to emphasise that the denial of service against which we seek to protect is the denial of service to the customer, not to the client. The attack may indeed consist of disabling or destroying the client, just as it may consist of interfering with the network or with the server. This paper does not consider issues of responsibility.
Menu stacking&mdash;help or hindrance?
Authors: John S. Gray
Venue: ACM SIGCHI Bulletin (1993)

Successful interaction with a computer to solve a specific problem requires the user to accomplish three basic tasks. First, the user must identify the goal to be accomplished. Second, a series of steps needed to accomplish the goal should be generated. Third, the user must carry out the specified steps. It is this third task that requires the user to interact with the computer. Most frequently this interaction is facilitated by the use of a software package that acts as an interface medium. The software permits the formulated steps to be implemented by the underlying system.
Conversation for organizational activity (abstract)
Authors: Chisato Numaoka
Venue: ACM SIGOIS Bulletin (1992)

In this paper I address the issues of how an organization, such as a group or a hierarchical society, can be formed and how organizational knowledge (e.g. a contract) can be acquired through conversation among situated agents. A special interest group (SIG) has the most fundamental style of these organizations. Through conversation, situated agents can join any SIG and act as a member in order to individually profit from group activity. On the basis of SIGs, we can formulate markets and hierarchies, which are organizations of different styles. Conversation is key to the organizational activity of situated agents in these organizations.
Computer science laboratories
Authors: R. Ross
Venue: ACM SIGACT News (1993)

In the second issue of the News (volume 24, number 2) this year I described the new breadth-first introductory curriculum in place at Montana State University, focusing on the role that theory plays in the four lecture courses constituting the curriculum. In the third issue (volume 24, number 3) an abbreviated syllabus was given for the four course sequence. During the interim, I have received numerous e-mail requests for more complete information, which indicates a growing interest in breadth-first, integrated approaches to the computer science curriculum as proposed in the Denning Report and Computing Curricula 1991 (cited in the last two issues). In this installment of the Forum some of the interesting aspects of the laboratory component of the curriculum are described.
Arrival theorems for product-form stochastic Petri nets
Authors: G. Balbo, S. C. Bruell, M. Sereno
Venue: ACM SIGMETRICS Performance Evaluation Review (1994)

We consider a particular class of Stochastic Petri Nets whose stationary probabilities at arbitrary instants exhibit a product form. We study these nets at specific instants in the steady state that occur directly after the firing of a transition. We focus our attention on the instant after tokens are removed from the places specified by a transition's input bag and just before tokens are entered into the places specified by the same transition's output bag. We show that the stationary probabilities at &ldquo;arrival instants&rdquo; are related to corresponding stationary probabilities at arbitrary instants in net(s) with lower load. We then show how one of the &ldquo;arrival&rdquo; theorems can be applied to the derivation of a formula for the mean sojourn time of a token in a place at steady state. This is the basis for the development of a Mean Value Analysis algorithm for the computation of performance indices for Product-Form Stochastic Petri Nets.
Garbage collection for strongly-typed languages using run-time type reconstruction
Authors: Shail Aditya, Christine H. Flood, James E. Hicks
Venue: Proceedings of the 1994 ACM conference on LISP and functional programming (1994)

Garbage collectors perform two functions: live-object detection and dead-object reclamation. In this paper, we present a new technique for live-object detection based on run-time type reconstruction for a strongly typed, polymorphic language. This scheme uses compile-time type information together with the run-time tree of activation frames to determine the exact type of every object participating in the computation. These reconstructed types are then used to identify and traverse the live heap objects during garbage collection.We describe an implementation of our scheme for the Id parallel programming language compiled for the *T multiprocessor architecture. We present simulation studies that compare the performance of type-reconstructing garbage collection with conservative garbage collection and compiler-directed storage reclamation.
Alternative perspectives of user participation: practical implications
Authors: Naveed Saleem
Venue: ACM SIGCPR Computer Personnel (1994)

A number of theories have been advanced in the information systems literature to rationalize the merits of user participation as a strategy for successful introduction of information systems in organizations. Importantly, while these theories contain some common elements, they also comprise significant differences. Understanding these commonalities and differences can facilitate effective implementation of user participation and thereby can make a difference in the ultimate failure or success of a system. This paper analyzes the major user participation theories; derives, as well as integrates, their implications for system users, user managers, and system designers; and infers respective applicability of these theories to specific system introduction contexts.
Interoperability using APPC
Authors: Debajyoti Mukhopadhyay
Venue: Proceedings of the 1993 ACM SIGMOD international conference on Management of data (1993)

The complex and competitive business world of today needs to access data for various operations from different systems placed at different geographical locations. In order to fulfil this need, one should have a reliable distributed computing environment. Various components of that environment may be supplied by different vendors. This means that the computing environment not only needs to be distributed but also requires interoperability. Today, Interoperability is no more just an idea but a reality. There is also a growing need to support interactions among various systems in a dialog mode. Integrating distributed systems can only help to achieve the goal of developing a reliable distributed computing environment. In this paper, a conceptual framework for an architecture is described in conjunction with Advanced Program-to-Program Communications LU 6.2 protocol to handle that challenge. This architecture discusses the required contracting services for integrating distributed systems. This contracting service has three major components: the contract interaction services, the contract support services, and the communications infrastructure services.
Distributed and Collaborative Visualization
Authors: Vinod Anupam, Chandrajit Bajaj, Daniel Schikore, Matthew Schikore
Venue: Computer (1994)

Visualization typically involves large computational tasks, often performed on supercomputers. The results of these tasks are usually analyzed by a design team consisting of several members. Our goal is to depart from traditional single-user systems and build a low-cost scientific visualization environment that enables computer-supported cooperative work in the distributed setting. A synchronously conferenced collaborative visualization environment would let multiple users on a network of workstations and supercomputers share large data sets, simultaneously view visualizations of the data, and interact with multiple views while varying parameters. Such an environment would support collaboration in both the problem-solving phase and the review phase of design tasks. In this article we describe two distributed visualization algorithms and the facilities that enable collaborative visualization. These are all implemented on top of the distribution and collaboration mechanisms of an environment called Shastra, executing on a set of low-cost networked workstations.
Angular resolution of straight-line drawings (abstract)
Authors: Michael Kaufmann
Venue: ACM SIGACT News (1993)

An orthogonal drawing of a graph is such that the edges are represented by polygonal chains consisting of horizontal and vertical segments. The intermediate vertices of the chain (which are not vertices of the graph) are called bends. In this talk we survey algorithms for constructing planar orthogonal drawings. The main quality measures considered are the minimization of the number of bends and of the area of the drawing. The construction of planar orthogonal drawings has many important applications, including graph visualization, VLSI layout, facilities floorplanning, and communication by light or microwave. Given an embedded planar graph G with n vertices, a planar orthogonal drawing of G with the minimum number of bends can be computed in O(n2 log n) time using network-flow techniques. Drawings with O (n) bends can be constructed in O(n) time using visibility representations. Also, there are families of graphs that require Omega;(n) bends. Open problems include minimizing bends over all possible embeddings, and finding an efficient parallel algorithm for bend minimization.
Metascheduling for continuous media
Authors: David P. Anderson
Venue: ACM Transactions on Computer Systems (TOCS) (1993)

Next-generation distributed systems will support continuous media (digital audio and video) in the same framework as other data. Many applications that use continuous media need guaranteed end-to-end performance (bounds on throughput and delay). To reliably support these requirements, system components such as CPU schedulers, networks, and file systems must offer performance guarantees. A metascheduler coordinates these components, negotiating end-to-end guarantees on behalf of clients. The CM-resource model, described in this paper, provides a basis for such a metascheduler. It defines a workload parameterization, an abstract interface to resources, and an algorithm for reserving multiple resources. The model uses an economic approach to dividing end-to-end delay, and it allows system components to &ldquo;work ahead,&rdquo; improving the performance of nonreal-time workload.