Exu is a new approach to automated support for safe, transparent and lightweight interoperability in multilanguage software systems. The approach is safe because it enforces appropriate type compatibility across language boundaries. It is transparent since it shields software developers from the details inherent in low-level language-based interoperability mechanisms. It is lightweight for developers because it eliminates tedious and error-prone coding (e.g., JNI) and lightweight at run-time since it does not unnecessarily incur the performance overhead of distributed, IDL-based approaches. The Exu approach exploits and extends the object-oriented concept of meta-object, encapsulating interoperability implementation in meta-classes so that developers can produce interoperating code by simply using meta-inheritance. An example application of Exu to the development of Java/C++ (i.e., multilanguage) programs illustrates the safety and transparency advantages of the approach. Comparing the performance of the Java/C++ programs produced by Exu to the same set of programs developed using IDL-based approaches provides preliminary evidence of the performance advantages of Exu.

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Interoperability is a fundamental concern in many areas of software engineering, such as software reuse or infrastructures for software development environments. Of particular interest to software engineers are the interoperability problems arising in polylingual software systems. The defining characteristic of polylingual systems is their focus on uniform interaction among a set of components written in two or more different languages.Existing approaches to support for interoperability are inadequate because they lack seamlessness: that is, they generally force software developers to compensate explicitly for the existence of multiple languages or the crossing of language boundaries. In this paper we first discuss some foundations for polylingual interoperability, then review and assess existing approaches. We then outline PolySPIN, an approach in which interoperability can be made transparent and existing systems can be made to interoperate with no visible modifications. We also describe PolySPINner, our prototype implementation of a toolset providing automated support for PolySPIN. We illustrate the advantages of our approach by applying it to an example problem and comparing PolySPIN's ease of use with that of an alternative, CORBA-style approach.

Name management is among the most basic foundations of software engineering, since so many software engineering tools and techniques fundamentally depend upon manipulation of names and the entities that they represent. While many individual tools and techniques have included their own specialized, often elaborate and idiosyncratic, approaches to name management, no unifying models for name management currently exist. As a result, the individual approaches are frequently complex and error-prone, while attempts to integrate collections of software engineering tools or techniques are often impeded by the inconsistency and incompatibility of the name management approaches used in the individual components of the collection. In this paper we consider some examples in which name management problems complicate software engineering activities. In particular, we focus on context control-related problems that often occur during software development. We then outline a unifying model of name manag...

The successful development of complex real-time systems depends on analysis techniques that can accurately assess the timing properties of those systems. This paper describes a technique for deriving upper and lower bounds on the time that can elapse between two given events in an execution of a concurrent software system running on a single processor under arbitrary scheduling. The technique involves generating linear inequalities expressing conditions that must be satisfied by all executions of such a system and using integer programming methods to find appropriate solutions to the inequalities. The technique does not require construction of the state space of the system and its feasibility has been demonstrated by using an extended version of the constrained expression toolset to analyze the timing properties of some concurrent systems with very large state spaces.>

The constrained expression approach to analysis of concurrent software systems can be used with a variety of design and programming languages and does not require a complete enumeration of the set of reachable states of the concurrent system. The construction of a toolset automating the main constrained expression analysis techniques and the results of experiments with that toolset are reported. The toolset is capable of carrying out completely automated analyses of a variety of concurrent systems, starting from source code in an Ada-like design language and producing system traces displaying the properties represented bv the analysts queries. The strengths and weaknesses of the toolset and the approach are assessed on both theoretical and empirical grounds.>

Although prototyping has long been touted as a potentially valuable software engineering activity, it has never achieved widespread use by developers of large-scale, production software. This is probably due in part to an incompatibility between the languages and tools traditionally available for prototyping (e.g., LISP or Smalltalk) and the needs of large-scale-software developers, who must construct and experiment with large prototypes. The recent surge of interest in applying prototyping to the development of large-scale, production software will necessitate improved prototyping languages and tools appropriate for constructing and experimenting with large, complex prototype systems. We explore techniques aimed at one central aspect of prototyping that we feel is especially significant for large prototypes, namely that aspect concerned with the definition of data objects. We characterize and compare various techniques that might be useful in defining data objects in large prototype systems, after first discussing some distinguishing characteristics of large prototype systems and identifying some requirements that they imply. To make the discussion more concrete, we describe our implementations of three techniques that represent different possibilities within the range of object definition techniques for large prototype systems.

Three important goals of next generation software development environments (SDEs) are extensibility, integration and broad scope. Our work on OROS is predicated on the hypothesis that a type model, incorporated into an environment's object manager, can contribute to achieving those goals. This paper reports on an attempt at applying object-oriented typing concepts in the domain of software development environments. We believe that the result is a type model that has properties of interest both to software environment builders and also to builders and users of object-oriented systems in general.

The AdaPIC tool set, an important component of an Ada software development environment, is discussed. The AdaPIC tool set is one particular instantiation, specifically adapted for use with Ada, of the more general collection of language features and analysis capabilities that constitute the PIC approach to describing and analyzing relationships among software system components. This tool set is being tailored to support an incremental approach to the interface control aspects of the software development process. Following a discussion of the PIC interface control and incremental development concepts, the AdaPIC tool set is described, concentrating on its analysis tools and support for incremental development and demonstrating how it contributes to the technology for developing large Ada software systems.>

A constrained expression approach to analyzing large-scale software is presented. Its advantages include broad applicability and reasonable efficiency relative to other proposed approaches. An overview is given of the current status of work on tools supporting analysis of distributed software systems. The constrained expression approach is outlined, and it is shown how it can be used to analyze distributed software. This is illustrated by a description of a recent experiment. An improved prototype toolset currently being built is described. Plans for enhanced tools and further experimentation are summarized.>

It is extremely difficult to characterize the possible behaviors of a distributed software system through informal reasoning. Developers of distributed systems require tools that support formal reasoning about properties of the behaviors of their systems. These tools should be applicable to designs and other preimplementation descriptions of a system, as well as to completed programs. Furthermore, they should not limit a developer's choice of development languages. In this paper we present a basis for broadly applicable analysis methods for distributed software systems. The constrained expression formalism can be used with a wide variety of distributed system development notations to give a uniform closed-form representation of a system's behavior. A collection of formal analysis techniques can then be applied with this representation to establish properties of the system. Examples of these formal analysis techniques appear elsewhere. Here we illustrate the broad applicability of the constrained expression formalism by showing how constrained expression representations are obtained from descriptions of systems in three different notations: SDYMOL, CSP, and Petri nets. Features of these three notations span most of the significant alternatives for describing distributed software systems. Our examples thus offer persuasive evidence for the broad applicability of the constrained expression approach.

A formal model for describing and evaluating visibility control mechanisms is introduced. The model reflects a general view of visibility in which the concepts of requisition of access and provision of access are distinguished. This model provides a means for characterizing and reasoning about the various properties of visibility control mechanisms. Specifically, the notion of preciseness is defined. The utility of the model is illustrated by using it to evaluate and compare the relative strengths and weaknesses, with respect to preciseness, of the visibility control mechanisms found in Algol 60, Ada, Gypsy, and an approach called PIC, which specifically addresses the concerns of visibility control in large software systems.>

An approach to the design of concurrent software systems based on the constrained expression formalism is described. This formalism provides a rigorous conceptual model for the semantics of concurrent computations, thereby supporting analysis of important system properties as part of the design process. This approach allows designers to use standard specification and design languages, rather than forcing them to deal with the formal model explicitly or directly. As a result, the approach attains the benefits of formal rigor without the associated pain of unnatural concepts or notations for its users. The conceptual model of concurrency underlying the constrained expression formalism treats the collection of possible behaviors of a concurrent system as a set of sequences of events. The constrained expression formalism provides a useful closed-form description of these sequences. Algorithms were developed for translating designs expressed in a wide variety of notations into these constrained expression descriptions. A number of powerful analysis techniques that can be applied to these descriptions have also been developed.

In this paper we outline an approach to describing and analyzing designs for distributed software systems. A descriptive notation is introduced, and analysis techniques applicable to designs expressed in that notation are presented. The usefulness of the approach is illustrated by applying it to a realistic distributed software-system design problem involving mutual exclusion in a computer network.

A modeling scheme is presented which provides a medium for the rigorous, formal, and abstract specification of large-scale software system components. The scheme allows the description of component behavior without revealing or requiring the description of a component's internal operation. Both collections of sequential processes and the data objects which they share may be described. The scheme is of particular value during the early stages of software system design, when the system's modules are being delineated and their interactions designed, and when rigorous, well-defined specification of undesigned components allows formal and informal arguments concerning the design's correctness to be formulated.