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.

This article explores memory sharing and protection support in Opal, a single-address-space operating system designed for wide-address (64-bit) architectures. Opal threads execute within protection domains in a single shared virtual address space. Sharing is simplified, because addresses are context independent. There is no loss of protection, because addressability and access are independent; the right to access a segment is determined by the protection domain in which a thread executes. This model enables beneficial code- and data-sharing patterns that are currently prohibitive, due in part to the inherent restrictions of multiple address spaces, and in part to Unix programming style. We have designed and implemented an Opal prototype using the Mach 3.0 microkernel as a base. Our implementation demonstrates how a single-address-space structure can be supported alongside of other environments on a modern microkernel operating system, using modern wide-address architectures. This article justifies the opal model and its goals for sharing and protection, presents the system and its abstractions, describes the prototype implementation,

Grammarware comprises grammars and all grammar-dependent software, i.e., software artifacts that directly involve grammar knowledge. The term grammar is meant here in the widest sense to include XML schemas, syntax definitions, interface descriptions, APIs, and interaction protocols. The most obvious examples of grammar-dependent software are document processors, parsers, import/export functionality, and generative programming tools. Even though grammarware is so omnipresent, it is somewhat neglected --- from an engineering point of view. We lay out an agenda that is meant to promote research on improving the quality of grammarware and on increasing the productivity of grammarware development.

Abstract. Refactoring is the process of improving the design of existing programs without changing their functionality. These notes cover refactoring in functional languages, using Haskell as the medium, and introducing the HaRe tool for refactoring in Haskell. 1

Abstract 1 Refactorings are behavior-preserving program transformations that automate design level changes in object-oriented applications. Our previous research established that many schema transformations, design patterns, and hotspot meta-patterns are automatable. This research evaluates whether refactoring technology can be transferred to the mainstream by restructuring non-trivial C++ applications. The applications that we examine were evolved manually by software engineers. We show that an equivalent evolution could be reproduced significantly faster and cheaper by applying a handful of general-purpose refactorings. In one application, over 14K lines of code were transformed automatically that otherwise would have been coded by hand. Our experiments identify benefits, limitations, and topics of further research related to the transfer of refactoring technology to a production environment. 1.

The appearance of 64-bit address space architectures, such as the DEC Alpha, HP PA-RISC, and MIPS R4000, signals a radical shift in the amount of address space available to operating systems and applications. This shift provides the opportunity to reexamine fundamental operating system structure specifically, to change the way that operating systems use address space. This paper

Software engineering research has focused mainly on software construction and has neglected software maintenance and evolution. Proposed is a shift in research from synthesis to analysis. Reverse engineering is introduced as a possible solution to program understanding and software analysis. Presented is reverse engineering technology developed as part of the Rigi project. The Rigi approach involves the identification of software artifacts in the subject system and the aggregation of these artifacts to form more abstract architectural models. Reported are some analyses on the source code of SQL/DS, performed by the authors while visiting the Program Understanding project at the IBM Centre for Advanced Studies in Toronto.

Program refactoring --- transforming a program to improve readability, structure, performance, abstraction, maintainability, or other characteristics --- is not applied in practice as much as might be desired. One deterrent is the cost of detecting candidates for refactoring and of choosing the appropriate refactoring transformation. This paper demonstrates the feasibility of automatically finding places in the program that are candidates for specific refactorings. The approach uses program invariants: when particular invariants hold at a program point, a specific refactoring is applicable. Since most programs lack explicit invariants, an invariant detection tool called Daikon is used to infer the required invariants. We developed an invariant pattern matcher for several common refactorings and applied it to an existing Java code base. Numerous refactorings were detected, and one of the developers of the code base assessed their efficacy.

Software developers spend most of their time modifying and maintaining existing products. This is because systems, and consequently their design, are in perpetual evolution before they die. Nevertheless, dealing with this evolution is a complex task. Before evolving a system, structural modifications are often required. The goal of this kind of modification is to make certain elements more extensible, permitting the addition of new features. However, designers are seldom able to evaluate the impact, on the whole model, of a single modification. That is, they cannot precisely verify if a change modifies the behavior of the modeled system. A possible solution for this problem is to provide designers with a set of basic transformations, which can ensure behavior preservation. These

People benefit from tightly integrated systems that can be designed, realized and evolved affordably. Unfortunately, common software design methods do not easily accommodate requirements for tightly integrated systems. Indeed, when used to meet such requirements, common methods tend to yield unnecessarily complex structures that complicate design and realization and that inhibit subsequent evolution. After substantiating this claim, I present the mediator method as a solution. This method combines behavioral entity-relationship (ER) modeling for design with a mediator approach to implementation. The mediator method is better than common methods for designing, realizing, and evolving many integrated systems. I support this claim both by rational argument from simplifying models and by careful...