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342
Algebraic laws for nondeterminism and concurrency
 Journal of the ACM
, 1985
"... Abstract. Since a nondeterministic and concurrent program may, in general, communicate repeatedly with its environment, its meaning cannot be presented naturally as an input/output function (as is often done in the denotational approach to semantics). In this paper, an alternative is put forth. Firs ..."
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Cited by 495 (12 self)
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Abstract. Since a nondeterministic and concurrent program may, in general, communicate repeatedly with its environment, its meaning cannot be presented naturally as an input/output function (as is often done in the denotational approach to semantics). In this paper, an alternative is put forth. First, a definition is given of what it is for two programs or program parts to be equivalent for all observers; then two program parts are said to be observation congruent iff they are, in all program contexts, equivalent. The behavior of a program part, that is, its meaning, is defined to be its observation congruence class. The paper demonstrates, for a sequence of simple languages expressing finite (terminating) behaviors, that in each case observation congruence can be axiomatized algebraically. Moreover, with the addition of recursion and another simple extension, the algebraic language described here becomes a calculus for writing and specifying concurrent programs and for proving their properties.
Programming with bananas, lenses, envelopes and barbed wire
 In FPCA
, 1991
"... We develop a calculus for lazy functional programming based on recursion operators associated with data type definitions. For these operators we derive various algebraic laws that are useful in deriving and manipulating programs. We shall show that all example Functions in Bird and Wadler's "Introdu ..."
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Cited by 299 (11 self)
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We develop a calculus for lazy functional programming based on recursion operators associated with data type definitions. For these operators we derive various algebraic laws that are useful in deriving and manipulating programs. We shall show that all example Functions in Bird and Wadler's "Introduction to Functional Programming " can be expressed using these operators. 1
A Framework for Comparing Models of Computation
 IEEE Transactions on ComputerAided Design of Integrated Circuits and Systems
, 1998
"... Abstract—We give a denotational framework (a “meta model”) within which certain properties of models of computation can be compared. It describes concurrent processes in general terms as sets of possible behaviors. A process is determinate if, given the constraints imposed by the inputs, there are e ..."
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Cited by 245 (54 self)
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Abstract—We give a denotational framework (a “meta model”) within which certain properties of models of computation can be compared. It describes concurrent processes in general terms as sets of possible behaviors. A process is determinate if, given the constraints imposed by the inputs, there are exactly one or exactly zero behaviors. Compositions of processes are processes with behaviors in the intersection of the behaviors of the component processes. The interaction between processes is through signals, which are collections of events. Each event is a valuetag pair, where the tags can come from a partially ordered or totally ordered set. Timed models are where the set of tags is totally ordered. Synchronous events share the same tag, and synchronous signals contain events with the same set of tags. Synchronous processes have only synchronous signals as behaviors. Strict causality (in timed tag systems) and continuity (in untimed tag systems) ensure determinacy under certain technical conditions. The framework is used to compare certain essential features of various models of computation, including Kahn process networks, dataflow, sequential processes, concurrent sequential processes with rendezvous, Petri nets, and discreteevent systems. I.
Monad Transformers and Modular Interpreters
 In Proceedings of the 22nd ACM Symposium on Principles of Programming Languages. ACMPress
, 1995
"... We show how a set of building blocks can be used to construct programming language interpreters, and present implementations of such building blocks capable of supporting many commonly known features, including simple expressions, three different function call mechanisms (callbyname, callby value ..."
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Cited by 233 (11 self)
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We show how a set of building blocks can be used to construct programming language interpreters, and present implementations of such building blocks capable of supporting many commonly known features, including simple expressions, three different function call mechanisms (callbyname, callby value and lazy evaluation), references and assignment, nondeterminism, firstclass continuations, and program tracing. The underlying mechanism of our system is monad transformers, a simple form of abstraction for introducing a wide range of computational behaviors, such as state, I/O, continuations, and exceptions. Our work is significant in the following respects. First, we have succeeded in designing a fully modular interpreter based on monad transformers that includes features missing from Steele's, Espinosa's, and Wadler's earlier efforts. Second, we have found new ways to lift monad operations through monad transformers, in particular difficult cases not achieved in Moggi's original work. ...
Logic and the Challenge of Computer Science
, 1988
"... Nowadays computer science is surpassing mathematics as the primary field of logic applications, but logic is not tuned properly to the new role. In particular, classical logic is preoccupied mostly with infinite static structures whereas many objects of interest in computer science are dynamic objec ..."
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Cited by 153 (16 self)
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Nowadays computer science is surpassing mathematics as the primary field of logic applications, but logic is not tuned properly to the new role. In particular, classical logic is preoccupied mostly with infinite static structures whereas many objects of interest in computer science are dynamic objects with bounded resources. This chapter consists of two independent parts. The first part is devoted to finite model theory; it is mostly a survey of logics tailored for computational complexity. The second part is devoted to dynamic structures with bounded resources. In particular, we use dynamic structures with bounded resources to model Pascal.
A stateoftheart survey on software merging
 IEEE Transactions on Software Engineering
, 2002
"... AbstractÐSoftware merging is an essential aspect of the maintenance and evolution of largescale software systems. This paper provides a comprehensive survey and analysis of available merge approaches. Over the years, a wide variety of different merge techniques has been proposed. While initial tech ..."
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Cited by 126 (5 self)
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AbstractÐSoftware merging is an essential aspect of the maintenance and evolution of largescale software systems. This paper provides a comprehensive survey and analysis of available merge approaches. Over the years, a wide variety of different merge techniques has been proposed. While initial techniques were purely based on textual merging, more powerful approaches also take the syntax and semantics of the software into account. There is a tendency towards operationbased merging because of its increased expressiveness. Another tendency is to try to define merge techniques that are as general, accurate, scalable, and customizable as possible, so that they can be used in any phase in the software lifecycle and detect as many conflicts as possible. After comparing the possible merge techniques, we suggest a number of important open problems and future research directions. Index TermsÐSoftware merging, largescale software development, merge conflicts, conflict detection, conflict resolution. æ 1
Querying Semistructured Heterogeneous Information
, 1995
"... . Semistructured data has no absolute schema fixed in advance and its structure may be irregular or incomplete. Such data commonly arises in sources that do not impose a rigid structure (such as the WorldWide Web) and when data is combined from several heterogeneous sources. Data models and query l ..."
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Cited by 113 (13 self)
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. Semistructured data has no absolute schema fixed in advance and its structure may be irregular or incomplete. Such data commonly arises in sources that do not impose a rigid structure (such as the WorldWide Web) and when data is combined from several heterogeneous sources. Data models and query languages designed for well structured data are inappropriate in such environments. Starting with a "lightweight" object model adopted for the TSIMMIS project at Stanford, in this paper we describe a query language and object repository designed specifically for semistructured data. Our language provides meaningful query results in cases where conventional models and languages do not: when some data is absent, when data does not have regular structure, when similar concepts are represented using different types, when heterogeneous sets are present, and when object structure is not fully known. This paper motivates the key concepts behind our approach, describes the language through a series o...
Design of Embedded Systems: Formal Models, Validation, and Synthesis
 PROCEEDINGS OF THE IEEE
, 1999
"... This paper addresses the design of reactive realtime embedded systems. Such systems are often heterogeneous in implementation technologies and design styles, for example by combining hardware ASICs with embedded software. The concurrent design process for such embedded systems involves solving the ..."
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Cited by 106 (9 self)
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This paper addresses the design of reactive realtime embedded systems. Such systems are often heterogeneous in implementation technologies and design styles, for example by combining hardware ASICs with embedded software. The concurrent design process for such embedded systems involves solving the specification, validation, and synthesis problems. We review the variety of approaches to these problems that have been taken.
Formal Verification by Symbolic Evaluation of PartiallyOrdered Trajectories
 Formal Methods in System Design
, 1993
"... Symbolic trajectory evaluation provides a means to formally verify properties of a sequential system by a modified form of symbolic simulation. The desired system properties are expressed in a notation combining Boolean expressions and the temporal logic "nexttime" operator. In its simplest form ..."
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Cited by 99 (25 self)
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Symbolic trajectory evaluation provides a means to formally verify properties of a sequential system by a modified form of symbolic simulation. The desired system properties are expressed in a notation combining Boolean expressions and the temporal logic "nexttime" operator. In its simplest form, each property is expressed as an assertion [A =) C], where the antecedent A expresses some assumed conditions on the system state over a bounded time period, and the consequent C expresses conditions that should result. A generalization allows simple invariants to be established and proven automatically. The verifier operates on system models in which the state space is ordered by "information content". By suitable restrictions to the specification notation, we guarantee that for every trajectory formula, there is a unique weakest state trajectory that satisfies it. Therefore, we can verify an assertion [A =) C] by simulating the system over the weakest trajectory for A and testing...
Projections for Strictness Analysis
, 1987
"... Contexts have been proposed as a means of performing strictness analysis on nonflat domains. Roughly speaking, a context describes how much a subexpression will be evaluated by the surrounding program. This paper shows how contexts can be represented using the notion of projection from domain theo ..."
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Cited by 98 (4 self)
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Contexts have been proposed as a means of performing strictness analysis on nonflat domains. Roughly speaking, a context describes how much a subexpression will be evaluated by the surrounding program. This paper shows how contexts can be represented using the notion of projection from domain theory. This is clearer than the previous explanation of contexts in terms of continuations. In addition, this paper describes finite domains of contexts over the nonflat list domain. This means that recursive context equations can be solved using standard fixpoint techniques, instead of the algebraic manipulation previously used. Praises of lazy functional languages have been widely sung, and so have some curses. One reason for praise is that laziness supports programming styles that are inconvenient or impossible otherwise [Joh87, Hug84, Wad85a]. One reason for cursing is that laziness hinders efficient implementation. Still, acceptable efficiency for lazy languages is at last being achieved...