WHAT IS A MODEL OF THE LAMBDA CALCULUS?

Pages: 20 August 1980 $3.00

Keywords: lambda calculus, mathematics

Abstract: An elementary, purely algebraic definition of model for the pure, untyped lambda calculus is given. This definition is shown to be equivalent to the usual syntactic definition. A simple construction of models for

a-i3(-~)-calculus is reviewed.

TM·172 Paseman, W.G.

SOME NEW METHODS OF MUSIC SYNTHESIS

Pages: 110 S.M. Thesis/August 1980 $3.00

Keywords: artificial intelligence, music synthesis Abstract: The first section discusses music composition, shows why it is a useful domain for Artificial Intelligence research and presents a set of

"Design Rules" that facilitate research in the field of tonal music composition. The second section describes some of the problems and issues encountered while designing the initial hardware for the Music Aided Cognition Project at MIT. All of the developed hardware permits computer control, performance and recording of music in real time. {AD A090·130}

TM·173 Hawkinson, L.B.

XLMS: A LINGUISTIC MEMORY SYSTEM

~~~~1~ ~m

Pages: 49

Keywords: knowledge representation, semantic network, linguistic memory

Abstract: LMS (Linguistic Memory System) is a knowledge representation formalism particularly designed for representing knowledge that can be straightforwardly expressed in natural language. Fundamentally, it is a semantic network formalism, a formalism for managing interconnected objects in a highly·organized, network·like memory. XLMS is a particular L1SP·based implementation of LMS, intended primarily for experimental use. {AD A090·033}

TM·174

Arvind, Kathail, V., Pingali, K.

A DATA FLOW ARCHITECTURE WITH TAGGED TOKENS

Pages: 24 September 1980 $3.00

Keywords: data flow, multiple processor architectures, parallel processing, applicative languages, hlgh·performance computers, functional languages, program decomposition, token labeling

Abstract: A machine comprising of hundreds of processing elements must have a highly distributed and asynchronous control structure. We are designing a system based on data flow principles in which each processing element contains a part of the program, and processors communicate by sending information packets to each other. Our machine is a hardware realization of a novel way of interpreting data flow languages known as the U·interpreter. The design of a processing element (PE) and a communication system for such a machine is presented .We also present arguments as to why our architecture can tolerate long average delays in the communication network without affecting the overall performance.

Schemes for mapping programs onto this machine are also discussed briefly.

TM·175

Meyer, A.R., Weise, D., Loui, M.C.

ON TIME VERSUS SPACE III

Pages: 8 September 1980 $3.00

Keywords: pebble game, time/space tradeoffs, storage modification machines, time complexity, space complexity

Abstract: Paul and Reishuk devised space efficient simulations of logarithmic cost random access machines and multidimensional Turing machines. We simplify their general space reduction technique and extend it to other models of computation, particularly to the class of storage modification machines (SMM), a model of list processing. Every SMM of time complexity tIn) can be simulated by an SMM of space complexity t(n)//og t(n).

TM·176 Seaquist, C.R.

A SEMANTICS OF SYNCHRONIZATION

Pages: 111 S.M. Thesis/September 1980 $3.00

Keywords: synchronization, concurrency

Abstract: This paper presents a rigorous framework in which to discuss the synchronization necessary to coordinate accesses to a resource. The framework, among other things, provides a method for specifying concurrency and forms the semantic basis of a synchronization mechanism which avoids certain unfortunate characteristics of monitors and serializers. Synchronization is viewed as being managed by a resource guardian. A synchronization problem is defined as a predicate on event sequences. The interaction of a guardian and the rest of the system is

formalized in terms of a two person game. This formalization results in precise definitions of guardian and guardian behavior. The notion of a

"good" or optimal solution is defined, and the solutions to certain classes of synchronization problems are characterized. An abstract description of the general actions of a guardian is given. This general description, with some restrictions, forms the basis of a simple synchronization mechanism for actually implementing solutions. The mechanism is given a rigorous semantics based on the definition of guardian. This facilitates the verification of correctness. Many examples of the use of the mechanism are given and its advantages are discussed. {AD A091·015}

TM·177 Sinha, M.K.

TIMEPAD • A PERFORMANCE IMPROVING SYNCHRONIZATION MECHANISM FOR DISTRIBUTED SYSTEMS

Pages: 55 Keywords:

performance, timestamps

September 1980 $3.00

distributed data base, synchronization, atomicity, Abstract: A new mechanism for the synchronization of accesses to distributed data objects is developed. This mechanism, called timepad, is an extension to the timestamp synchronization scheme and it encaches the concurrency transparency requirement of the user reducing the chance of eventual rejection of a transaction. The timepad scheme will improve the performance of those distributed data base systems where the probability of transactions clashing is high.

The timepad scheme is very nicely integrated with the object history concept developed by David Reed and the improved power of the integrated scheme is shown to solve the meeting fixing problem. We also discuss how the timepad mechanism can be used as an approximation pad to solve problems which need approximate solution.

TM·178

Arvind, Thomas, R.E.

I·STRUCTURES: AN EFFICIENT DATA TYPE FOR FUNCTIONAL LANGUAGES

Pages: 19 October 1981 $3.00

Keywords: applicative languages, asynchronous systems, data flow, data structures, data types, functional semantics, multiple processor systems, parallelism, storage management

Abstract· Data structure operations in purely functional languages often consume relatively large amounts of memory and processing time. In many circumstances, however, the full generality of these data structure operations is not needed and hence significant gains should be possible by substituting restricted data structure operations. An I·structure is a new array·like data structure which can substantially reduce data structure overhead in functional programs when data structures are generated or consumed "monotonically". I·structures retain functional semantics thereby aiding the detection and exploitation of parallelism and are especially useful in systems based on data flow principles to reduce data dependencies from an entire data structure to individual elements of the structure. In many cases the reduction of such data dependencies can result in significant gains in parallelism. Unlike other proposals for reducing data dependencies, I·structures are convenient for expressing numerical algorithms since they allow random access to individual elements without additional overhead.

TM·179

Halpern, J.Y., Meyer, A.R.

AXIOMATIC DEFINITIONS OF PROGRAMMING LANGUAGES, II

Pages: 18 October 1980 $3.00

Keywords: semantics, programming languages, partial correctness, axiomatic definitions of programming languages, expressiveness, termination

Abstract: Sufficient conditions are given for partial correctness assertions to determine the input·output semantics of quite general classes of programming languages. This determination cannot be unique unless states which are indistinguishable by predicates in the assertions are identified. Even when indistinguishable states are identified, partial correctness assertions may not suffice to determine program semantics.

TM·180

Papadimitriou, C.H.

A THEOREM IN DATA BASE CONCURRENCY CONTROL

Pages: 6 October 1980 $3.00

Keywords: concurrency, concurrency control, data base transactions, locking, semaphores

Abstract: Consider two straight-line problems A and B, and let H be a set of sequences of steps of A and B, possibly interleaved, but each containing all steps of A and B in the right order. We give a necessary and sufficient condition for H to be realizable as the set of all sequences of steps of A and B. This condition captures the intuitive limitations of locking primitives owing to their limited memory capacity.

TM·181

lipski, W., Papadimltriou, C.H.

A FAST ALGORITHM FOR TESTING FOR SAFETY AND DETECTING DEADLOCKS IN LOCKED TRANSACTION SYSTEMS

Pages 14 October 1980 $3.00

Keywords. data base concurrency control, geometry of locking, computational geometry

Abstract. We represent an O(nlognlognloglogn) time algorithm which, given a set of n rectangles on the plane with horizontal and vertical sides, and two POints sand t, determines whether there exists a monotonically increasing curve form s to t which separates two of the rectangles while avoiding all other rectangles. This solves several problems related to data base concurrency control

TM-182

Itai, A, Papadimitriou, C.H., Szwarefiter, J.L.

HAMILTON PATHS IN GRID GRAPHS

Pages: 14 October 1980 $3.00

Keywords: Hamilton circuit, grid graphs, rectangular grid graphs, NP-complete, traveling salesman problem

Abstract: A grid path is a node-induced finite subgraph of the infinite grid. It is rectangular if Its set of nodes IS the product of two intervals. Given a rectangular grid graph and two of ItS nodes, we give necessary and sufficient conditions for the graph to have a Hamilton path between these two nodes. In contrast, the Hamilton path (and circuit) problem for general grid graphs is shown to be NP-complete. This provides a new, relatively simple, proof of the result that the Euclidean traveling salesman problem is NP-complete.

TM-183 Meyer, A.R.

A NOTE ON THE LENGTH OF CRAIG'S INTERPOLANTS

Pages: 4 October 1980 $3.00

Keywords Craigs interpolants

Abstract: There is no recursive bound on the length of the smallest interpolant.

TM·184

Lieberman, H., Hewitt, C

A REAL TIME GARBAGE COLLECTOR THAT CAN RECOVER TEMPORARY STORAGE QUICKLY

Pages: 22 October 1980 $3.00

Keywords: garbage collection, storage, recovery

Abstract: In previous heap storage systems, the cost of creating objects and garbage collection is independent of the lifetime of the object. Since temporary objects account for a large portion of storage use, it's worth optimizing a garbage collector to reclaim temporary storage faster. We present a garbage collection algorithm which:

(1) Makes short term storage cheaper than long term storage.

(2) Operates in real time-object creation and access times are bounded.

(3) Works well with multiple processors and a large address space.

TM-185

Kung, H -T., Papadimitriou, C.H.

AN OPTIMALITY THEORY OF CONCURRENCY CONTROL FOR DATABASES

Pages: 13 November 1980 $3.00

Keywords: data base concurrency control, scheduling, optimal scheduler Abstract: A concurrency control mechanism (or a scheduler) is the component of a data base system that feguards the consistency of the data base in the presence of interleaved accesses and update requests. We formally show that the performance of a scheduler, i.e., the amount of parallelism that it supports, depends explicitly upon the amount of Information that is available to the scheduler. We point out that most previous work on concurrency control is simply concerned with specific points of thiS basic trade-off between performance and information. In fact, several of these approaches are shown to be optimal for the amount of information that they use. {AD A092-625}

TM-186

Szolovits, P., Martin, W.A.

BRAND X MANUAL

Pages: 21 November 1980 $3.00

Keywords: LISP, artificial intelligence, knowledge representation, semantic network, programming languages

Abstract: BRAND X is a representation language implemented as a pure extension of LISP. BRAND X provides the following additional facilities over LISP: Unique and canonical structures, property lIsts for all objects, labels for all objects, and a syntax to express each of these, supported by a reader and printer. BRAND X is intended as an "assembly language" for representation languages, attempting to provide facilities generally found useful in the simplest manner, without any strong commitment to specific representational conventions. {AD A093-041/2}

TM-187

Fischer, M.J., Meyer, A.R., Paterson, M.S.

Q (n log n) LOWER BOUNDS ON LENGTH OF BOOLEAN FORMULAS

Pages 18 November 1980 $3.00

Keywords: mathematics, Boolean functions

Abstract: A property of Boolean functions of n variables is described and shown to imply lower bounds as large as Q(n log n) on the number of literals

In any Boolean formula for any function with the property. Formulas over the full basis of binary operations (A, <ll, etc) are conSidered The lower bounds apply to all but a vanishing fraction of symmetric functions, In

particular to all threshold functions with sufficiently large threshold and to the "congruent to zero modulo k" function for k>2. In the case k = 4 the bound is optimal.

TM·188 Mayr, E.w.

AN EFFECTIVE REPRESENTATION OF THE REACHABILITY SET OF PERSISTENT PETRI NETS

Pages: 17 January 1981 $3.00

Keywords: vector replacement system, Petri nets, persistence, representation of reachability set

Abstract: In a persistent net, an enabled transition can become disabled only by firing itself. Here, an algorithm is presented which constructs a semilinear representation of the set of states reachable in an arbitrary persistent Petri net

TM-189 Mayr, E.w.

PERSISTENCE OF VECTOR REPLACEMENT SYSTEMS IS DECIDABLE

Pages: 18 January 1981 $3.00

Keywords: vector replacement system, Petri nets, persistence, representation of reachability set

Abstract: In a persistent vector replacement system (VRS) or Petri net, an enabled transition can become disabled only by firing itself. Here, an algorithm is presented which allows to decide whether an arbitrary VRS is persistent or not, and if so, to construct a semi linear representation of the set of states reachable in the system.

TM·190

Ben-Ari, M., Halpern, J.Y., Pnueli, A.

DETERMINISTIC PROPOSITIONAL DYNAMIC LOGIC: FINITE MODELS, COMPLEXITY, AND COMPLETENESS

Pages: 20 January 1981 $3.00

Keywords: deterministic propositional dynamic logic, propositional dynamic logic, tableau method, completeness

Abstract: Let p be a formula in deterministic propositional dynamic logic. A decision procedure for the satisfiability of p is given along with a construction of finite model for every satisfiable p. The decision procedure runs in deterministic time 2cn and the size of the model is bounded by n2*4n, where n is the length of p. Finally, a complete axiomatization for deterministic propositional dynamic logic IS given, based on the Segerberg axioms for propositional dynamic logic.

TM·191 Parikh, R.

PROPOSITIONAL DYNAMIC LOGICS OF PROGRAMS: A SURVEY

Pages: 37 January 1981 $3.00

Keywords: propositional dynamic logic

Abstract: The use of logic in program verification is an old idea, as such ideas go. Early work by Engeler, Floyd, Hoare and Salwicki has already developed into a rich field with many workers. However the propositIOnal

versions of these logics are relatively new; work in this field goes back only to Fischer and Ladner's 1977 paper where they showed that the propositional version of Pratt's dynamic logic is decidable. Since then the field has developed rapidly, a very large number of preliminary questions have already been settled, and interesting side areas are developing. In what follows, we shall try to give an overview, stating some of the main results and referring the reader to the original sources for the more difficult or elaborate proofs.

TM·192

Meyer, A.R., Streett, R.S., Mirkowska, G.

THE DEDUCIBILITY PROBLEM IN PROPOSITIONAL DYNAMIC LOGIC

Pages: 16 February 1981 $3.00

Keywords: propositional dynamic logic, dynamic logic Abstract: The problem of whether an arbitrary formula of Propositional Dynamic Logic (PDL) is deducible from a fixed axiom scheme of POL is TI11.complete. This contrasts with the decidability of the problem when the axiom scheme is replaced by any single PDL formula.

TM·193

Yannakakis, M, Papadimitriou, C.H.

ALGEBRAIC DEPENDENCIES

Pages: 32 February 1981 $3.00

Keywords' relational data base, data dependencies, template and algebraic dependencies, embedded implicational dependencies, tableaux, extended relations, complete axiomatization, project-join expressions Abstract: We propose a new kind of data dependencies called algebraic dependencies, which generalize all previously known kinds. We give a complete axiomatization of algebraic dependencies in terms of simple algebraic rewriting rules. In the process we characterize exactly the expressive power of tableaux, thus solving an open problem of Aho, Sagiv and Ullman; we show that it is NP-complete to tell whether a tableau is realizable by an expression; and we give an interesting dual interpretation of the chase procedure. We also show that algebraic dependencies over a language augmented to contain union and set difference can express arbitrary domain·independent predicates of finite index over finite relations.

The class of embedded implicational dependencies recently-and independently·introduced by Fagin is shown to coincide with our algebraic dependencies. Based on this, we give a simple proof of Fagin's Armstrong relation theorem.

TM-194

Barendregt, H., Longo, G.

RECURSION THEORETIC OPERATORS AND MORPHISMS ON NUMBERED SETS

Pages: 16 February 1981 $3.00

Keywords: operators, morphlsms, numbered sets, recursion Abstract: An operator is a map <J>:Pw'T'Pw. By embedding Pw in two natural ways into the A·calculus model Pw2 (and rw) the computable maps on this latter structure induce several classes of recursion theoretic operators.

TM·195 Barber, G.

RECORD OF THE WORKSHOP ON RESEARCH IN OFFICE SEMANTICS

Pages: 15 February 1981 $3.00

Keywords: office automation, knowledge-based systems Abstract: This paper is a compendium of the ideas and issues presented at the Chatham Bars Workshop on Office Semantics. The intent of the workshop was to examine the state of the art in office systems and to elucidate the issues system designers were concerned with in developing next generation office systems. The workshop involved a cross-section of people from government, industry and academia. Presentations in the form of talks and video tapes were made of prototypical systems.

TM·196 Bhatt, S.N.

ON CONCENTRATION AND CONNECTION NETWORKS

Pages: 69 S.M. Thesis/March 1981 $3.00

Keywords' switching networks, rearrangeable concentrators, expanders, superconcentrators, probabilistic constructions, incrementally non-blocking connectors

Abstract. This thesis deals with the structural complexity of switching networks which realize concentration and connection requests when operated in a rearrangeable or incremental manner. Some of the important results and constructions are briefly reviewed. On the basis of non-constructive proof techniques used to obtain linear upper bounds on the

complexity of rearrangeable concentrators, it is shown that not only are certain random graphs likely to be rearrangeably non-blocking concentrators, but that if a randomly constructed graph is not non·blocking, then, on the average, only a constant number of edges need be added to the graph to make it blocking. Although the problem of recognizing non-blocking networks appears to be a computationally hard problem, the extra edges may be added to the graph efficiently, during operation of the network. Finally, we obtain a constructive as well as an improved non·

constructive upper bound on the complexity of incrementally non-blocking connection networks.

TM·197

Fredkin, E., Toffoli, T.

CONSERVATIVE LOGIC

Pages: 28 May 1981 $3.00

Keywords: conservative logic, reversible computing, computation universality, automata, networks, physical computing, information mechanics, discrete mechanics

Abstract: Conservative logic is a comprehensive model of computation which explicitly reflects a number of fundamental principles of physics, such as the reversibility of the dynamical laws and the conservation of certain additive quantities. Because of its closer adherence to physics than found in traditional models of computation, conservative logic is in a better position to provide indications concerning the realizations of high performance computing systems, i.e., of systems that make very efficient use of the "computing resources" actually offered by nature. In particular, conservative logic shows that it is ideally possible to build sequential circuits with zero internal power dissipation.

TM·198

Halpern, J.Y., Reif, J.H.

THE PROPOSITIONAL DYNAMIC LOGIC OF DETERMINISTIC, WELL·

STRUCTURED PROGRAMS

Pages: 39 March 1981 $3.00

Keywords. propositional dynamic logie, decision procedure, polynomial space complete, expressiveness, well·structured programs Abstract: We consider a restricted propositional dynamic logic, Strict Deterministic Propositional Dynamic Logic (SDPDL), which is appropriate for reasoning about deterministic well-structured programs. In contrast to PDL, for which the validity problem is known to be complete in deterministic exponential time, the validity problem for SDPDL is shown to be polynomial space complete. We also show that SDPDL is less expensive than PDL. The results rely on structure theorems for models of satisfiable SDPDL formulas, and the proofs give insight into the effects of nondeterminism on intractability and expressiveness In program logics.

TM·199

Mayr, E.W., Meyer, A.R.

THE COMPLEXITY OF THE WORD PROBLEMS FOR COMMUTATIVE SEMIGROUPS AND POLYNOMIAL IDEALS

Pages: 32 June 1981 $3.00

Keywords: word problem, commutative semi group, computational complexity, polynomial ideal, exponential space, vector replacement system, Petri nets

Abstract: Any decision procedure for the word problems for commutative semigroups and polynomial ideals inherently requires computational storage space growing exponentially with the size of the problem instance to which the procedure is applied. This bound is achieved by a simple procedure for the semigroup problem.

TM·200 Burke, G.

LSB MANUAL

Pages: 92 June 1981 $3.00

Keywords: layered system building, LISP, NIL, LSB, MACLISP Abstract: LSB (for Layered System Building) is an integrated set of facilities for aiding in the construction of highly-modular, multi·layered, implementation-independent LISP systems. It provides for conditional inclusion of source text, documentation production, automated declarations, and "high-level" definitions. LISP code compiled with LSB in

Keywords: layered system building, LISP, NIL, LSB, MACLISP Abstract: LSB (for Layered System Building) is an integrated set of facilities for aiding in the construction of highly-modular, multi·layered, implementation-independent LISP systems. It provides for conditional inclusion of source text, documentation production, automated declarations, and "high-level" definitions. LISP code compiled with LSB in

Im Dokument liSP CREDITS (Seite 75-85)