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Many would argue that future breakthroughs in software productivity will depend on our ability to combine existing pieces of software to produce new applications. An important step towards this goal is the development of new techniques to detect and cope with mismatches in the assembled parts. Some problems of composition are due to low-level issues of interoperability, such as mismatches in programming languages or database schemas. However, in this paper we highlight a different, and in manywaysmore pervasive, class of problem: architectural mismatch. Specifically, we use our experience in building a family of software design environments from existing parts to illustrate a variety of types of mismatch that center around the assumptions a reusable part makes about the structure of the application in which is to appear. Based on this experience we show how an architectural view of the mismatch problem exposes some fundamental, thorny problems for software composition and suggests poss...

Step-wise refinement is a powerful paradigm for developing a complex program from a simple program by adding features incrementally. We present the AHEAD (Algebraic Hierarchical Equations for Application Design) model that shows how step-wise refinement scales to synthesize multiple programs and multiple noncode representations. AHEAD shows that software can have an elegant, hierarchical mathematical structure that is expressible as nested sets of equations. We review a tool set that supports AHEAD. As a demonstration of its viability, we have bootstrapped AHEAD tools from equational specifications, refining Java and non-Java artifacts automatically; a task that was accomplished only by ad hoc means previously.

Abstract. Mixin layers are a technique for implementing layered object-oriented subclasses (mixin classes) but scaled to a multiple-class granularity. We describe mixin layers from a programming language viewpoint, discuss checking the consistency of a mixin layer composition, and analyze the language support issues involved. 1

While a large fraction of application code is devoted to graphical user interface (GUI) functions, support for reuse in this domain has largely been confined to the creation of GUI toolkits ("widgets"). We present a novel architectural style directed at supporting larger grain reuse and flexible system composition. Moreover, the style supports design of distributed, concurrent applications. Asynchronous notification messages and asynchronous request messages are the sole basis for inter-component communication. A key aspect of the style is that components are not built with any dependencies on what typically would be considered lower-level components, such as user interface toolkits. Indeed, all components are oblivious to the existence of any components to which notification messages are sent. While our focus has been on applications involving graphical user interfaces, the style has the potential for broader applicability. Several trial applications using the style are described.

Abstract. Feature models are used to specify members of a product-line. Despite years of progress, contemporary tools provide limited support for feature constraints and offer little or no support for debugging feature models. We integrate prior results to connect feature models, grammars, and propositional formulas. This connection allows arbitrary propositional constraints to be defined among features and enables off-the-shelf satisfiability solvers to debug feature models. We also show how our ideas can generalize recent results on the staged configuration of feature models.

A "refinement" is a functionality addition to a software project that can affect multiple dispersed implementation entities (functions, classes, etc.). In this paper, we examine large-scale refinements in terms of a fundamental object-oriented technique called collaboration-based design. We explain how collaborations can be expressed in existing programming languages or be supported with new language constructs (which we have implemented as extensions to the Java language). We present a specific expression of large-scale refinements called mixin layers, and demonstrate how it overcomes the scalability difficulties that plagued prior work. We also show how we used mixin layers as the primary implementation technique for building an extensible Java compiler, JTS.

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GenVoca generators synthesize software systems by composing components from reuse libraries. GenVoca components are designed to export and import standardized interfaces, and thus be plugcompatible, interchangeable, and interoperable with other components. In this paper, we examine two different but important issues in software system synthesis. First, not all syntactically correct compositions of components are semantically correct. We present simple, efficient, and domainindependent algorithms for validating compositions of GenVoca components. Second, components that export and import immutable interfaces are too restrictive for software system synthesis. We show that the interfaces and bodies of GenVoca components are subjective, i.e., they mutate and enlarge upon instantiation. This mutability enables software systems with customized interfaces to be composed from components with “standardized ” interfaces. 1

Abstract. This paper is about a paradigm shift from the current practice of manually searching for and adapting components and their manual assembly to Generative Programming, which is the automatic selection and assembly of components on demand. First, we argue that the current OO technology does not support reuse and configurability in an effective way. Then we show how a system family approach can aid in defining reusable components. Finally, we describe how to automate the assembly of components based on configuration knowledge. We compare this paradigm shift to the introduction of interchangeable parts and automated assembly lines in the automobile industry. We also illustrate the steps necessary to develop a product line using a simple example of a car product line. We present the feature model of the product line, develop a layered architecture for it, and automate the assembly of the components using a generator. We also discuss some design issues, applicability of the approach, and future development. 1 From Handcrafting to an Automated Assembly Line This paper is about a paradigm shift from the current practice of manually searching for and adapting components and their manual assembly to Generative Programming,