IFIP Congress 

About: IFIP Congress is an academic conference. The conference publishes majorly in the area(s): Software development & Fifth-generation programming language. Over the lifetime, 1474 publications have been published by the conference receiving 36175 citations.

The Semantics of a Simple Language for Parallel Programming.

Abstract: In this paper, we describe a simple language for parallel programming. Its semantics is studied thoroughly. The desirable properties of this language and its deficiencies are exhibited by this theoretical study. Basic results on parallel program schemata are given. We hope in this way to make a case for more formal (i.e. mathematical) approach to the design of languages for systems programming and the design of operating systems. There is a wide disagreement among systems designers as to what are the best primitives for writing systems programs. In this paper, we describe a simple language for parallel programming and study its mathematical properties. 1. A SIMPLE LANGUAGE FOR PARALLEL PROGRAMMING The features of our mini-language are exhibited on the sample program S on Figure 1. The conventions are close to Algol1 and we only insist upon the new features. The program S consists of a set of declarations and a body. Variables of type integer channel are declared at line (1), and for any simple type σ (boolean, real, etc. . . ) we could have declared a σ channel. Then processes f , g and h are declared, much like procedures. Aside from usual parameters (passed by value in this example, like INIT at line (3)), we can declare in the heading of the process how it is linked to other processes : at line (2) f is stated to communicate via two input lines that can carry integers, and one similar output line. The body of a process is an usual Algol program except for invocation of wait until something on an input line (e.g. at (4)) or send a variable on a line of compatible type (e.g. at (5)). The process stays blocked on a wait until something is being sent on this line by another process, but nothing can prevent a process from performing a send on a line. In others words, processes communicate via first-in first-out (fifo) queues. Calling instances of the processes is done in the body of the main program at line (6) where the actual names of he channels are bound to the formal parameters of the processes. The infix operator par initiates the concurrent activation of the processes. Such a style of programming is close to may systems using EVENT mechanisms ([1, 2, 3, 4]). A pictorial representation of the program is the schema P on Figure 2, where the nodes represent processes and the arcs communication channels between these processes. What sort of things would we like to prove on a program like S? Firstly, that all processes in S run forever. Secondly, Begin (1) In t eg e r channel X, Y, Z , T1 , T2 ; (2 ) Process f ( i n t e r g e r in U,V; i n t e r g e r out W) ; Begin i n t e g e r I ; l o g i c a l B; B := true ; Repeat Begin (4 ) I := i f B then wait (U) e l s e wait (V) ; (7 ) p r in t ( I ) ; (5 ) send I on W; B := not B; End ; End ; Process g ( i n t e g e r in U ; i n t e g e r out V, W) ; Begin i n t e g e r I ; l o g i c a l B; B := true ; Repeat Begin I := wait (U) ; i f B then send I on V e l s e send I on W : B := not B; End ; End ; (3 ) Process h( i n t e g e r in U; i n t e g e r out V; i n t e g e r INIT ) ; Begin i n t e g e r I ; send INIT on V; Repeat Begin I := wait (U) ; send I on V; End ; End ; Comment : body o f mainprogram ; (6 ) f (X,Y,Z) par g (X,T1 ,T2) par h(T1 ,Y, 0 ) par h(T2 , Z , 1 ) ; End ; Figure 1: Sample parallel program S. more precisely, that S prints out (at line (7)) an alternating sequence of 0’s and 1’s forever. Third, that if one of the processes were to stop at some time for an extraneous reason, the whole systems would stop. The ability to state formally this kind of property of a parallel program and to prove them within a formal logical framework is the central motivation for the theoretical study of the next sections. 2. PARALLEL COMPUTATION Informally speaking, a parallel computation is organized in the following way: some autonomous computing stations are connected to each other in a network by communication lines. Computing stations exchange information through these lines. A given station computes on data coming along

The Ultimate Display

Abstract: We live in a physical world whose properties we have come to know well through long familiarity. We sense an involvement with this physical world which gives us the ability to predict its properties well. For example, we can predict where objects will fall, how well-known shapes look from other angles, and how much force is required to push objects against friction. We lack corresponding familiarity with the forces on charged particles, forces in non-uniform fields, the effects of nonprojective geometric transformations, and high-inertia, low friction motion. A display connected to a digital computer gives us a chance to gain familiarity with concepts not realizable in the physical world. It is a looking glass into a mathematical wonderland. Computer displays today cover a variety of capabilities. Some have only the fundamental ability to plot dots. Displays being sold now generally have built in line-drawing capability. An ability to draw simple curves would be useful. Some available displays are able to plot very short line segments in arbitrary directions, to form characters or more complex curves. Each of these abilities has a history and a known utility.

Types, Abstraction and Parametric Polymorphism.

Abstract: In this report we discuss the findings of a Web-based questionnaire aimed at discovering both patterns of use of videoconferencing systems within HP and the reasons people give for either not using, or for using such systems. The primary motivation was to understand these issues for the purpose of designing new kinds of technology to support remote work rather than as an investigation into HP’s internal processes. The questionnaire, filled out via the Web by 4532 people across HP, showed that most participants (68%) had not taken part in a videoconference within the last 3 years, and only 3% of the sample were frequent users. Of those who had used videoconference systems, the main benefits were perceived to be the ability to: see people they had never met before, see facial expressions and gestures, and follow conversations with multiple participants more easily. The main problems that users of videoconference technology perceived were: the high overhead of setting up and planning videoconferencing meetings, a lack of a widespread base of users, the perception that videoconference technology did not add value over existing communication tools, and quality and reliability issues. Non-users indicated that the main barriers were lack of access to videoconference facilities and tools and a perception that they did not need to use this tool because other tools were satisfactory. The findings from this study in a real work setting are related to findings in the research literature, and implications for system design and research are identified.

Shape Grammars and the Generative Specification of Painting and Sculpture

Abstract: A method of shape generation using shape grammars which take shape as primitive and have shape-specific rules is presented. A formalism for the complete, generative specification of a class of non-representational, geometric paintings or sculptures is defined which has shape grammars as its structural component. Paintings are material representations of two-dimensional shapes gen~rated by shape grammars, sculptures of three-dimensional shapes. Implications for aesthetics and design theory in the visual arts are discussed. Aesthetics is considered in terms of specificational simplicity and visual complexity. In design based on generative specifications, the artist chooses structural and material relationships and then determines algorithmically the resulting works of art. SHAPE GRAMMARS AND THE GENERATIVE SPECIFICATION OF PAINTING AND SCULPTURE In this paper we present (1) a definition of shape grammars, (2) a formalism, based on these grammars, for the complete, generative specification of a class of paintings or sculptures, and (3) a discussion of the implications of these specifications for aesthetics and design theory. Generative specifications can be used in the analysis and aesthetic evaluation of the paintings or sculptures they define. In design based on generative specifications, the artist chooses structural and material relationships and then produces algorithmically the res'ulting works of art, Our underlying aim is to use formal, generative techniques to produce good works of art and to develop understanding of what makes good works of art. The class of paintings shown in Figure 1 is used as an explanatory example. Additional paintings and sculptures defined by generative specifications are shown in the I ppendix.