Valdis Berzins

A prototyping language for real-time software

PSDL is a language for describing prototypes of real-time software systems. It is most useful for requirements analysis, feasibility studies, and the design of large embedded systems. PSDL has facilities for recording and enforcing timing constraints, and for modeling the control aspects of real-time systems using nonprocedural control constraints, operator abstractions, and data abstractions. The language has been designed for use with an associated prototyping methodology. PSDL prototypes are executable if supported by a software base containing reusable software components in an underlying programming language (e.g. Ada). >

Dynamic Occlusion Analysis in Optical Flow Fields

Optical flow can be used to locate dynamic occlusion boundaries in an image sequence. We derive an edge detection algorithm sensitive to changes in flow fields likely to be associated with occlusion. The algorithm is patterned after the Marr-Hildreth zero-crossing detectors currently used to locate boundaries in scalar fields. Zero-crossing detectors are extended to identify changes in direction and/or magnitude in a vector-valued flow field. As a result, the detector works for flow boundaries generated due to the relative motion of two overlapping surfaces, as well as the simpler case of motion parallax due to a sensor moving through an otherwise stationary environment. We then show how the approach can be extended to identify which side of a dynamic occlusion boundary corresponds to the occluding surface. The fundamental principal involved is that at an occlusion boundary, the image of the surface boundary moves with the image of the occluding surface. Such information is important in interpreting dynamic scenes. Results are demonstrated on optical flow fields automatically computed from real image sequences.

Accuracy of Laplacian edge detectors

The sources of error for the edge finding technique proposed by Marr and Hildreth (D. Marr and T. Poggio, Proc. R. Soc. London Ser. B 204 , 1979, 301–328; D. Marr and E. Hildreth, Proc. R. Soc. London Ser. B. 207 , 1980, 187–217) are identified, and the magnitudes of the errors are estimated, based on idealized models of the most common error producing situations. Errors are shown to be small for linear illuminations, as well as for nonlinear illuminations with a second derivative less than a critical value. Nonlinear illuminations are shown to lead to spurious contours under some conditions, and some fast techniques for discarding such contours are suggested.

Rapidly prototyping real-time systems

A prototyping approach that uses modularity and reusable components is described that enables large real-time systems to be prototyped rapidly. It combines a computational model tailored for real-time systems with a high-level prototyping language (the Prototype System Description Language), a systematic design method for rapid prototype construction, and an automated prototyping environment. The method meets the following requirements: the prototype satisfies its requirements and is traceable to them; the prototype is easy to modify; and the prototype code is easy to read and analyze.<<ETX>>

The realizable benefits of a language prototyping language

The uses and advantages of a language tailored specifically for the description and construction of translators are considered. The major features of the Kodiyak language prototyping language are described. The Kodiyak language was designed to be a comprehensive translator development system. The language is intended to support a simple, unambiguous conceptual model of translation, to allow the construction of nontrivial translators, and, to be easy to use. >

Software merge: semantics of combining changes to programs

We present a language-independent semantic model of the process of combining changes to programs. This model extends the domains used in denotational semantics (complete partial orders) to Boolean algebras, and represents incompatible modifications as well as compatible extensions. The model is used to define the intended semantics of change-merging operations on programs and to establish some general properties of software merging. We determine conditions under which changes to subprograms of a software system can be merged independently and illustrate cases where this is not possible.

Analysis and Design in MSG.84: Formalizing Functional Specifications

Model building is identified as the most important part of the analysis and design process for software systems. A set of primitives to support this process is presented, along with a formal language, MSG.84, for recording the results of analysis and design. The semantics of the notation is defined in terms of the actor formalism, which is based on a message passing paradigm. The automatic derivation of a graphical form of the specification for user review is discussed. Potentials for computer-aided design based on MSG.84 are indicated.

Abstraction-based software development

A five-year experience with abstraction-based software-development techniques in the university environment indicates that the investment required to support the paradigm in practice is returned in terms of greater ability to control complexity in large projects—provided there exists a set of software tools sufficient to support the approach.

On merging software extensions

SummaryThe problem of combining independent updates to a program is examined in the context of applicative programs. A partial semantic merge rule is given together with the conditions under which it is guaranteed to be correct, and the conditions under which a string merge corresponds to a semantic merge are examined. The theoretical work reported here contains initial steps towards a solution of the software merging problem and is not sufficient for producing a practical system.

Using transformations in specification-based prototyping

The authors explore the use of software transformations for software evolution. Meaning-preserving program transformations have been widely used for program development from a fixed initial specification. They consider a wider class of transformations to support development in which the specification evolves, rather than being fixed in advance. A new and general classification of transformations based on their effect on system interfaces, externally observable behavior, and abstraction level of a system description is presented. This classification is used to rearrange chronological derivation sequences containing meaning-changing transformations into lattices containing only meaning-preserving transformations. A process model for software evolution that utilizes prototyping techniques is described. Ways in which this class of transformations can be used to support such a process are considered. A set of examples are presented to illustrate the ideas. Software tool support and directions for future research are discussed. >