\documentstyle[twocolumn,icse97]{article} \begin{document} \title{Evolution of Software Via Adaptive Programming} \author{ \parbox{3.5in} {\begin{center} {\authornamefont Karl J. Lieberherr}\\ Northeastern University, College of Computer Science, 161 Cullinane Hall \\ Boston, MA 02115-9959 USA \\ (617) 373 2077 Fax: (617) 373 5121 \\ lieberherr@ccs.neu.edu \\ Demeter home page: http://www.ccs.neu.edu/research/demeter\\ \end{center} } } \maketitle %\copyrightspace \section{ABSTRACT} The objective of this project is to improve the productivity of software developers by an order of magnitude through tools and a theory of adaptive programming. To make our results practically useful, we want to leverage existing commercial technology such as Java and the Unified Modeling Language (UML). Our recent work has focussed on rethinking our Demeter/C++ tools and corresponding theory and to implement the new results in Demeter/Java. Demeter/Java is an implementation of Adaptive Programming (AP) for Java. Demeter/Java programs consist of Java code together with programs in a small language to express traversals, visitor methods, and class diagrams. Demeter/Java programs are typically written in a preventive maintenance style using traversal strategies for expressing traversals. The resulting programs are very robust under changes to the class diagrams and visitors. This preventive maintenance style also leads to simpler programs, making both software development and maintenance easier. \subsection{Keywords} software evolution, aspect-oriented programming \section{INTRODUCTION} %what is AP? Adaptive Programming (AP) has been described in several papers, theses and a book (see Demeter home page and \cite{karl:demeter}). The idea of AP is to consider structure and navigation through structures as separate aspects \cite{sdcr:aop,sdcr:acm}. Adaptive programs are written in terms of traversal strategies, and then customized into detailed traversals using specific class diagrams. The traversal strategies are simpler than the detailed traversals, leading to more flexible and simpler programs. \section{RECENT WORK} In the following we highlight recent developments. \subsection{Demeter/Java} %what is new in Demeter/Java: improving the Visitor Demeter/Java \cite{cse:preventive} is an implementation of AP for Java in the form of an efficiently executable design language. In Demeter/Java we add several innovations to AP including an improved form of the Visitor pattern from \cite{gang-of-4} is provided by the design language. Fig. \ref{p1} summarizes the impact of AP on the coupling between aspects. The grammar aspect includes class diagrams. The table holds for both Java and C++. For example, without AP, traversals and visitors are highly coupled: The visitor must have a method for each class in the traversal scope. With AP, the coupling between traversals and visitors is low: since both traversal strategies and visitors mention only the ``interesting'' classes. \begin{figure}[htb] \begin{verbatim} Aspects | Coupling to other aspects --------------------------------------------- | with AP without AP | -------------------- grammar | visitors low moderate --------------------------------------------- traversals | grammar low high | visitors low high --------------------------------------------- object | grammar low high description| \end{verbatim} \caption{Aspects of AP}\label{p1} \end{figure} Demeter/Java is much closer to Java than Demeter/C++ is to C++. Much of the syntax for propagation and transportation patterns could be eliminated from the core of the system. The most important generalization is probably the use of visitors instead of wrappers. While Demeter/C++ uses a home-grown generic parser, Demeter/Java uses a commercial parser/scanner generator, namely the Java Compiler Compiler (JavaCC). JavaCC is used to create objects from robust object descriptions and an annotated UML class diagram which represents an LL(1) grammar. Demeter uses an improved form of the Interpreter design pattern \cite{gang-of-4}: class definition and grammar definition are integrated. Doug Orleans is the lead designer and implementor of Demeter/Java. While in Demeter/C++ propagation patterns play a central role, in Demeter/Java they are only syntactic sugar to express certain commonly occurring traversals and visitors. The insight we gained was that propagation patterns were too big of an abstraction which is better decomposed into traversals and visitors with an attachment mechanism of visitors to traversals \cite{spl:context-conf}. While in Demeter/C++ traversals are static, in Demeter/Java with the TAO (traversal as objects) extension, traversals may be computed at run-time. (Johan Ovlinger) While in Demeter/C++ generic behavior for copying, printing, etc. was hardcoded for entire objects, in Demeter/Java you can selectively copy, print, etc. partial objects. This is accomplished by providing a CopyVisitor, PrintVisitor, etc. which is attached to a traversal selecting the subobjects of interest. (Geoff Hulten) While in Demeter/C++ conditional traversals were expressed in an unpleasing way, Demeter/Java supports around methods. They provide for easier composition and provide also the foundation for dealing with exceptions in an aspect-oriented way. (Lars Hansen) \subsection{AP Studio} Adaptive programming is a visual programming technique and therefore we add a graphical user interface to Demeter/Java. AP Studio currently allows to visualize class dictionnaries and to create them graphically. AP Studio allows to visually design traversal strategies with immediate visual feedback regarding the selected paths. The plan is to extend AP Studio into a tool for developing adaptive programs. (Kedar Patankar and Binoy Samuel) \subsection{Traversal Strategies} One of the improvements of the Visitor design patterns is the use of traversal strategies. In earlier papers we called traversal strategies propagation directives or traversal specifications. Traversal strategies improve on traversal specifications by a better, more general model and a better compilation algorithm. (Boaz Patt-Shamir) \section{USE AND AVAILABILITY} % sales pitch Several companies see the benefit of both simpler and more maintainable programs as very important and have adopted AP for C++. Some use our tools and others (for example, Hewlett Packard) use the ideas in a conventional C++ environment. Demeter/Java makes AP available to the Java community. Demeter/Java is implemented in Demeter/Java and is freely distributed in Java source form from the Demeter home page where further information on use is available. The software is copyrighted but freely redistributable. %It runs on any platform where Java is available. %It is also a convenient %tool to teach effective object-oriented design techniques. Demeter/Java is a successful teaching tool combined with \cite{karl:demeter}. It is used in software design and development classes using Java. \section{RELATED WORK} Numerous references to related work are in \cite{karl:demeter} and the Demeter home page. Recently, aspect-oriented programming from Xerox PARC has emerged as an area related to AP \cite{sdcr:aop,sdcr:acm}. See also http://www.parc.xerox.com/aop. The Demeter/Java visitors are inspired by the context objects in \cite{spl:context-conf}. \section{ACKNOWLEDGEMENTS} This work is supported by DARPA and Rome Laboratory under agreement F30602-96-0239 and NSF under grant CCR-9402486 and a grant from Xerox PARC. 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