Showing papers by "IBM published in 1976"

Symbolic execution and program testing

Abstract: This paper describes the symbolic execution of programs. Instead of supplying the normal inputs to a program (e.g. numbers) one supplies symbols representing arbitrary values. The execution proceeds as in a normal execution except that values may be symbolic formulas over the input symbols. The difficult, yet interesting issues arise during the symbolic execution of conditional branch type statements. A particular system called EFFIGY which provides symbolic execution for program testing and debugging is also described. It interpretively executes programs written in a simple PL/I style programming language. It includes many standard debugging features, the ability to manage and to prove things about symbolic expressions, a simple program testing manager, and a program verifier. A brief discussion of the relationship between symbolic execution and program proving is also included.

The notions of consistency and predicate locks in a database system

Abstract: In database systems, users access shared data under the assumption that the data satisfies certain consistency constraints. This paper defines the concepts of transaction, consistency and schedule and shows that consistency requires that a transaction cannot request new locks after releasing a lock. Then it is argued that a transaction needs to lock a logical rather than a physical subset of the database. These subsets may be specified by predicates. An implementation of predicate locks which satisfies the consistency condition is suggested.

What is "liquid"? Understanding the states of matter

Abstract: Liquids exist in a relatively small part of the enormous range of temperatures and pressures existing in the universe. Nevertheless, they are of vital importance for physics and chemistry, for technology, and for life itself. A century of effort since the pioneering work of van der Waals has led to a fairly complete basic understanding of the static and dynamic physicochemical properties of liquids. Advances in statistical mechanics (the fundamental formulations of Gibbs and Boltzmann, integral equations and perturbation theories, computer simulations), in knowledge of intermolecular forces, and in experimental techniques; have all contributed to this. Thirty years ago the very existence of liquids seemed a little mysterious; today one can make fairly precise predictions of the solid-liquid-gas phase diagram and of the microscopic and macroscopic static and dynamic properties of liquids. This paper is a survey, with particular emphasis on equilibrium properties, of the theory which underlies that basic understanding, which is now at least comparable with our understanding of the physics of solids.

System R: relational approach to database management

Abstract: System R is a database management system which provides a high level relational data interface. The systems provides a high level of data independence by isolating the end user as much as possible from underlying storage structures. The system permits definition of a variety of relational views on common underlying data. Data control features are provided, including authorization, integrity assertions, triggered transactions, a logging and recovery subsystem, and facilities for maintaining data consistency in a shared-update environment.This paper contains a description of the overall architecture and design of the system. At the present time the system is being implemented and the design evaluated. We emphasize that System R is a vehicle for research in database architecture, and is not planned as a product.

Continuous speech recognition by statistical methods

Abstract: Statistical methods useful in automatic recognition of continuous speech are described. They concern modeling of a speaker and of an acoustic processor, extraction of the models' statistical parameters and hypothesis search procedures and likelihood computations of linguistic decoding. Experimental results are presented that indicate the power of the methods.

Recoverability of Communication Protocols--Implications of a Theoretical Study

Abstract: A study is presented which permits the formal analysis and synthesis of recoverable computer communication protocols. This study is based on a formal representation of processes by a model of computation, the Petri nets (PN's). The PN model is generalized to include a representation of the possible failures, and then, the concept of "recoverability" is formally defined. A set of necessary and sufficient conditions which a process must satisfy in order to be recoverable is derived. In the PN model, the processes that satisfy these conditions are shown to have some practical limitations. A new model, the time-Petri net (TPN), is introduced to remove these limitations. This new model allows the introduction of constraints in the execution times of its part. As shown in this paper, the TPN appears to be a suitable model for the study of practical recoverable processes. Several practical communication protocols are formally designed and analyzed using this new model, and some interesting properties of these protocols are formally derived.

Generalized kraft inequality and arithmetic coding

Abstract: Algorithms for encoding and decoding finite strings over a finite alphabet are described. The coding operations are arithmetic involving rational numbers li as parameters such that Σi2-l i≤2-∈. This coding technique requires no blocking, and the per-symbol length of the encoded string approaches the associated entropy within ∈. The coding speed is comparable to that of conventional coding methods.

SEQUEL 2: a unified approach to data definition, manipulation, and control

Abstract: SEQUEL 2 is a relational data language that provides a consistent, English keyword-oriented set of facilities for query, data definition, data manipulation, and datac ontrol. SEQUEL 2 may be used either as a stand-alone interface for nonspecialists in data processing or as a data sublanguage embedded in a host programming language for use by application programmers and data base administrators. This paper describes SEQUEL 2 and the means by which it is coupled to a host language.

Provability interpretations of modal logic

Abstract: We consider interpretations of modal logic in Peano arithmetic (P) determined by an assignment of a sentencev * ofP to each propositional variablev. We put (⊥)*=“0 = 1”, (χ → ψ)* = “χ* → ψ*” and let (□ψ)* be a formalization of “ψ)* is a theorem ofP”. We say that a modal formula, χ, isvalid if ψ* is a theorem ofP in each such interpretation. We provide an axiomitization of the class of valid formulae and prove that this class is recursive.

Probabilities on Finite Models

Abstract: Let be a finite set of (nonlogical) predicate symbols. By an -structure, we mean a relational structure appropriate for . Let be the set of all -structures with universe {1, …, n}. For each first-order -sentence σ (with equality), let μn(σ) be the fraction of members of for which σ is true. We show that μn(σ) always converges to 0 or 1 as n → ∞, and that the rate of convergence is geometrically fast. In fact, if T is a certain complete, consistent set of first-order -sentences introduced by H. Gaifman [6], then we show that, for each first-order -sentence σ, μn(σ) →n 1 iff T ⊩ ω. A surprising corollary is that each finite subset of T has a finite model. Following H. Scholz [8], we define the spectrum of a sentence σ to be the set of cardinalities of finite models of σ. Another corollary is that for each first-order -sentence a, either σ or ˜σ has a cofinite spectrum (in fact, either σ or ˜σ is “nearly always“ true).Let be a subset of which contains for each in exactly one structure isomorphic to . For each first-order -sentence σ, let νn(σ) be the fraction of members of which a is true. By making use of an asymptotic estimate [3] of the cardinality of and by our previously mentioned results, we show that vn(σ) converges as n → ∞, and that limn νn(σ) = limn μn(σ).If contains at least one predicate symbol which is not unary, then the rate of convergence is geometrically fast.

A program data flow analysis procedure

Abstract: The global data relationships in a program can be exposed and codified by the static analysis methods described in this paper. A procedure is given which determines all the definitions which can possibly “reach” each node of the control flow graph of the program and all the definitions that are “live” on each edge of the graph. The procedure uses an “interval” ordered edge listing data structure and handles reducible and irreducible graphs indistinguishably.

An authorization mechanism for a relational database system

Abstract: A multiuser database system must selectively permit users to share data, while retaining the ability to restrict data access. There must be a mechanism to provide protection and security, permitting information to be accessed only by properly authorized users. Further, when tables or restricted views of tables are created and destroyed dynamically, the granting, authentication, and revocation of authorization to use them must also be dynamic. Each of these issues and their solutions in the context of the relational database management system System R are discussed.When a database user creates a table, he is fully and solely authorized to perform upon it actions such as read, insert, update, and delete. He may explicitly grant to any other user any or all of his privileges on the table. In addition he may specify that that user is authorized to further grant these privileges to still other users. The result is a directed graph of granted privileges originating from the table creator.At some later time a user A may revoke some or all of the privileges which he previously granted to another user B. This action usually revokes the entire subgraph of the grants originating from A's grant to B. It may be, however, that B will still possess the revoked privileges by means of a grant from another user C, and therefore some or all of B's grants should not be revoked. This problem is discussed in detail, and an algorithm for detecting exactly which of B's grants should be revoked is presented.

Finding the nearest point in A polytope

Abstract: A terminating algorithm is developed for the problem of finding the point of smallest Euclidean norm in the convex hull of a given finite point set in Euclideann-space, or equivalently for finding an “optimal” hyperplane separating a given point from a given finite point set. Its efficiency and accuracy are investigated, and its extension to the separation of two sets and other convex programming problems described.

Fractional Tap-Spacing Equalizer and Consequences for Clock Recovery in Data Modems

Abstract: Adaptive equalizers are usually realized in the form of a transversal filter with variable tap gains and tap spacing equal to the symbol spacing T . The performance of these equalizers depends critically on the symbol-clock phase derived in the receiver, due to the clock-phase dependent aliasing of the spectral roll-off components, upon which the conventional equalizer has no influence. In this paper we study the possibility of overcoming this difficulty by making the tap spacing of the equalizer somewhat smaller than T (fractional tap spacing). It is shown that this leads to satisfactory performance of the equalizer for a broad continuous range of clock phases, without penalizing the speed of convergence. Furthermore, it allows the application of a simple clock recovery scheme which derives a phase control signal from the equalizer tap-gain values.

Calculated spectral dependence of gain in excited GaAs

Abstract: The calculated dependence of the gain coefficient on photon energy and excitation level in GaAs is given for 297 and 77 K. The curves of gain versus excitation rate generally have downward curvature for photon energies near the gain peak, while the envelope of these curves generally has upward curvature except at high excitation rates. Results are also given for the calculated dependence of the radiative recombination rate coefficient and of the photon energy at the gain peak on excitation rate. The qualitative behavior of the results is in agreement with experiment.

Electronic structure, spectra, and properties of 4:2-coordinated materials. I. Crystalline and amorphous SiO 2 and GeO 2

Abstract: A two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed. The parameters, a covalent and a polar energy, are fitted to the optical absorption spectra. The valence energy bands and density of states are calculated. In terms of these a consistent interpretation of all the observed photoemission and x-ray-emission spectra of ${\mathrm{SiO}}_{2}$ is obtained. The x-ray-absorption spectra are also analyzed. A bond-orbital approximation allows a simple calculation of the refractive index (or dielectric constant) of the various allotropic forms of silica and germania. Finally, the variation in total energy and charge distribution with local distortion is analyzed in order to study structural stability, elastic rigidity, and the effective charges (including dynamic contributions) which determine the piezoelectric constants and infrared absorption intensities.

Chain-complete posets and directed sets with applications

Abstract: Let a poset P be called chain-complete when every chain, including the empty chain, has a sup in P. Many authors have investigated properties of posets satisfying some sort of chain-completeness condition (see [,11, [-31, [6], I-71, [17], [,181, ['191, [,211, [,221), and used them in a variety of applications. In this paper we study the notion of chain-completeness and demonstrate its usefulness for various applications. Chain-complete posets behave in many respects like complete lattices; in fact, a chaincomplete lattice is a complete lattice. But in many cases it is the existence of sup's of chains, and not the existence of arbitrary sup's, that is crucial. More generally, let P be called chain s-complete when every chain of cardinality not greater than ~ has a sup. We first show that if a poset P is chain s-complete, then every directed subset of P with cardinality not exceeding ct has a sup in P. This sharpens the known result ([,8], [,181) that in any chain-complete poset, every directed set has a sup. Often a property holds for every directed set i f and only if it holds for every chain. We show that direct (inverse) limits exist in a category if and only if 'chain colimits' ('chain limits') exist. Since every chain has a well-ordered cofinal subset [11, p. 681, one need only work with well-ordered collections of objects in a category to establish or disprove the existence of direct and inverse limits. Similarly, a topological space is compact if and only if every 'chain of points' has a cluster point. A 'chain of points' is a generalization of a sequence. Chain-complete posers, like complete lattices, arise from closure operators in a fairly direct manner. Using closure operators we show how to form the chaincompletion P of any poset P. The chain-completion/~ of a poset P is a chain-complete poset with the property that any chain-continuous map from a poser P into a chain-complete poset Q extends uniquely to a chain-continuous map from the completion/~ into Q, where by a chaincontinuous map we mean one that preserves sup's of chains. If P is already chaincomplete, then/~ is naturally isomorphic to P. This completion is not the MacNeille

Calculation of energy straggling for protons and helium ions

Abstract: Energy straggling has been calculated for protons and helium ions in each of the elements, by using the Hartree-Fock-Slater charge distribution for the target atom with Bonderup and Hvelplund's formulation. The results reveal a ${Z}_{2}$ structure in energy straggling, and afford a ready explanation of some earlier measurements.

Entropy of ionization and temperature variation of ionization levels of defects in semiconductors

Abstract: We make simple estimates of the entropy of ionization of Coulombic, isoelectronic, and vacancy-type defects in semiconductors by considering the effect of localized and free-carrier charge distributions upon the lattice modes. The empirical values of these entropies are observed as the temperature variation of the corresponding ionization levels. We predict a crossing of vacancy donor and acceptor levels in Si and Ge, which is supported by quenching and diffusion experiments. We also conclude that some of the deep Coulombic defects, such as the Au acceptor in Si, are most likely a complex of the Coulombic center with some isoelectronic or vacancy defect, such as Au interstitial with Si vacancy, rather than a simple substitutional impurity as previously assumed.

Surface Oxidation of Silicon Nitride Films

Abstract: ESCA is used to characterize silicon nitride surface oxidation. Si 2p, N 1s, and O 1s binding energies and photoelectron line intensities of oxidized nitride films are compared with the corresponding lines from thick reference films of silicon, silicon nitride, silcon dioxide, and a series of oxynitrides. Rapid initial oxidation of silicon nitride surfaces occurs at room temperature on exposure of nitride films to air. A graded oxidized nitride film forms between the film surface and the nitride. Similarly, oxynitride films with gradations in composition are obtained upon oxidation of nitride films at high temperatures.

The measurement of magnetostriction in ferromagnetic thin films

Abstract: The application of a magnetic field parallel to a ferromagnetic film deposited on one side of a cantilevered substrate causes a small deflection of the free end. This deflection can be measured and the magnetostriction determined since the magnetostriction is proportional to the deflection. An instrument has been devised which can measure the deflection as a function of the applied field. This is accomplished as follows: the cantilevered substrate with the film on the upper side forms one plate of a capacitor which is part of the tuning capacitance of an oscillator operating at l0 MHz. The deflection of the free end causes a change in frequency of about 10 to 100 Hz. which is easily measured. The sign of the magnetostriction is immediately discernible from the increase or decrease in oscillator frequency. The instrument is calibrated by hanging a known weight from the free end of the substrate. Magnetostriction constants as small as 3 \times 10^{-7} and as large as 40 \times 10^{-6} have been measured.

Digital image processing of earth observation sensor data

Abstract: This paper describes digital image processing techniques that were developed to precisely correct Landsat multispectral Earth observation data and gives illustrations of the results achieved, e.g., geometric corrections with an error of less than one picture element, a relative error of one-fourth picture element, and no radiometric error effect. Techniques for enhancing the sensor data, digitally mosaicking multiple scenes, and extracting information are also illustrated.