Abstract not found

This thesis defines a set of program restructuring operations (refactorings) that support the design, evolution and reuse of object-oriented application frameworks. The focus of the thesis is on automating the refactorings in a way that preserves the behavior of a program. The refactorings are defined to be behavior preserving, provided that their preconditions are met. Most of the refactorings are simple to implement and it is almost trivial to show that they are behavior preserving. However, for a few refactorings, one or more of their preconditions are in general undecidable. Fortunately, for some cases it can be determined whether these refactorings can be applied safely. Three of the most complex refactorings are defined in detail: generalizing the inheritance hierarchy, specializing the inheritance hierarchy and using aggregations to model the relationships among classes. These operations are decomposed into more primitive parts, and the power of these operations is discussed from the perspectives of automatability and usefulness in supporting design. Two design constraints needed in refactoring are class invariants and exclusive components. These constraints are needed to ensure that behavior is preserved across some refactorings. This thesis gives some conservative algorithms for determining whether a program satisfies these constraints, and describes how to use this design information to refactor a program.

The need to integrate several versions of a program into a common one arises frequently, but it is a tedious and time consuming task to integrate programs by hand. To date, the only available tools for assisting with program integration are variants of text-based differential file comparators; these are of limited utility because one has no guarantees about how the program that is the product of an integration behaves compared to the programs that were integrated. This paper concerns the design of a semantics-based tool for automatically integrating program versions. The main contribution of the paper is an algorithm that takes as input three programs A, B, and Base, where A and 8 are two variants of Base. Whenever the changes made to Base to create A and B do not “interfere ” (in a sense defined in the paper), the algorithm produces a program M that integrates A and B. The algorithm is predicated on the assumption that differences in the behavior of the variant programs from that of Base, rather than differences in the text, are significant and must be preserved in M. Although it is undecidable whether a program modification actually leads to such a difference, it is possible to determine a safe approximation by comparing each of the variants with Base. To determine this information, the integration algorithm employs a program representation that is similar (although not identical) to the dependence graphs that have been used

Abstract. Requirements engineering is concerned with the identification of high-level goals to be achieved by the system envisioned, the refinement of such goals, the operationalization of goals into services and constraints, and the assignment of responsibilities for the resulting requirements to agents such as humans, devices and programs. Goal refinement and operationalization is a complex process which is not well supported by current requirements engineering technology. Ideally some form of formal support should be provided, but formal methods are difficult and costly to apply at this stage. This paper presents an approach to goal refinement and operationalization which is aimed at providing constructive formal support while hiding the underlying mathematics. The principle is to reuse generic refinement patterns from a library structured according to strengthening/weakening relationships among patterns. The patterns are once for all proved correct and complete. They can be used for guiding the refinement process or for pointing out missing elements in a refinement. The cost inherent to the use of a formal method is thus reduced significantly. Tactics are proposed to the requirements engineer for grounding pattern selection on semantic criteria. The approach is discussed in the context of the multi-paradigm language used in the KAOS method; this language has an external semantic net layer for capturing goals, constraints, agents, objects and actions together with their links, and an inner formal assertion layer that includes a real-time temporal logic for the specification of goals and constraints. Some frequent refinement patterns are highlighted and illustrated through a variety of examples. The general principle is somewhat similar in spirit to the increasingly popular idea of design patterns, although it is grounded on a formal framework here. Keywords: Goal-driven requirements engineering, refinement,

This paper describes a language-independent program representation-the program dependence graph—and &mCusses how program dependence graphs, together with operations such as program slicing, can provide the basis for powerfid programming tools that address important software-engineering problems, such as understanding what an existing program does and how it works, understanding the differences between several versions of a program, and creating new programs by combining pieces of old programs. The paper primarily surveys work in this mea that has been czried out at the University of Wisconsin during the past five years.

We show how structured data stored in files can benefit from standard database technology and in particular be queried and updated using database languages. We introduce the notion of structuring schema which consists of a grammar annotated with database programs and of a database schema. We study the translation from structured strings to databases, and the converse. We adapt optimization techniques from relational databases to our context. 1 Introduction Database systems are concerned with structured data. Unfortunately, data is often stored in an unstructured manner (e.g., in files) even when it does have a strong internal structure (e.g., electronic documents or programs) . In this paper, we consider how data stored as strings can benefit from standard database technology and in particular be queried and updated using database languages. In actual systems, data is often stored as string for obvious historical reasons. The problem that we are considering is thus very general. Tools...

We consider the problem of storing and accessing documents (SGML and HTML, in particular) using database technology. To specify the database image of documents, we use structuring schemas that consist in grammars annotated with database programs. To query documents, we introduce an extension of OQL, the ODMG standard query language for object databases. Our extension (named OQL-doc) allows to query documents without a precise knowledge of their structure using in particular generalized path expressions and pattern matching. This allows us to introduce in a declarative language (in the style of SQL or OQL), navigational and information retrieval styles of accessing data. Query processing in the context of documents and path expressions leads to challenging implementation issues. We extend an object algebra with new operators to deal with generalized path expressions. We then consider two essential complementary optimization techniques: 1. we show that almost standard database optim...

Good documentation is important for the production of reusable and maintainable software. For the production of accurate documentation it is necessary that the original program text is not copied manually to obtain a typeset version. Aside of being tedious, this will invariably lead to errors. Tools that support the production of legible and accurate documentation are essential in software engineering. The production of such tools is a software engineering challenge in itself. We present an algebraic approach to the generation of tools that produce typographically effective presentations of computer programs. A specification of a formatter is generated from the context-free grammar of a programming language. These genererated formatters translate abstract syntax trees of programs into box expressions. These box expressions are translated by language independent interpreters of the box language into ascii or T E X. The formatting rules that are generated can easily be fine tuned in orde...

Higher Order Attribute Grammars (HAGs) are an extension of normal attribute grammars in the sense that the distinction between the domain of parse-trees and the domain of attributes has disappeared: parse trees may be computed in attributes and grafted to the parse tree at various places. As a result semantic functions may be described by attribute evaluation.

Since the early 1960’s, researchers have built a number of programming languages and environments with the intention of making programming accessible to a larger number of people. This article presents a taxonomy of languages and environments designed to make programming more accessible to novice programmers of all ages. The systems are organized by their primary goal, either to teach programming or to use programming to empower their users, and then, by each system’s authors ’ approach, to making learning to program easier for novice programmers. The article explains all categories in the taxonomy, provides a brief description of the systems in each category, and suggests some avenues for future work in novice programming environments and languages.