The first conference on Pattern Languages of Program Design (PLoP)was a watershed event that gave a public voice to the software designpattern movement. Seventy software professionals from around theworld worked together to capture and refine software experience thatexemplifies the elusive quality called "good design." This volume isthe result of that work--a broad compendium of this new genre ofsoftware literature.
Patterns are a literary form that take inspiration from literateprogramming, from a design movement of the same name in contemporaryarchitecture, and from the practices common to the ageless literatureof any culture. The goal of pattern literature is to help programmersresolve the common difficult problems encountered in design andprogramming. Spanning disciplines as broad as client/serverprogramming, distributed processing, organizational design, softwarereuse, and human interface design, this volume encodes designexpertise that too often remains locked in the minds of expertarchitects. By capturing these expert practices as problem-solutionpairs supported with a discussion of the forces that shape alternativesolution choices, and rationales that clarify the architects' intents,these patterns convey the essence of great software designs.
I. FRAMEWORKS & COMPONENTS.1. Functionality Ala Carte (Sam Adams).
II. SYSTEMS & DISTRIBUTED PROCESSING.5. A Generative Pattern Language for Distributed Processing (Dennis DeBruler).
III. BUSINESS OBJECTS.10. The CHECKS Pattern Language of Information Integrity (Ward Cunningham).
IV. PROCESS AND ORGANIZATION.13. A Generative Development-Process Pattern Language (James Coplien).
V. DESIGN PATTERNS AND CATALOGS.17. A System of Patterns (Frank Buschmann, Regine Meunier).
VI. ARCHITECTURE & COMMUNICATION.21. Streams: A Pattern for “Pull-Driven” Processing (Stephen Edwards).
VII. OBJECT USAGE AND STYLE.25. Understanding and Using the ValueModel Framework in VisualWorks Smalltalk (Bobby Woolf).
VIII. EVENTS & EVENT HANDLERS.28. A Pattern for Separating Assembly and Processing (Steve Berczuk).
This book is the culmination of an intensive effort to capture and refine a broad range of software development expertise in a systematic and highly accessible manner. The chapters are based on papers presented at the First Annual Conference of Pattern Languages of Programming (PLoP) held near Monticello, Illinois, in August 1994. This book is more than just a compendium of conference papers, however. It represents a broad offering from a new body of literature focusing on object-oriented design patterns. It is the first in a series of similar edited works on an ever-broadening spectrum of software patterns and pattern languages.
Design patterns capture the static and dynamic structures of solutions that occur repeatedly when producing applications in a particular context. Because they address fundamental challenges in software system development, design patterns are an important technique for improving the quality of software. Key challenges addressed by design patterns include communication of architectural knowledge among developers, accommodating a new design paradigm or architectural style, and avoiding development traps and pitfalls that are usually learned only by (painful) experience.
A large body of pattern literature already exists--not for software, but for constructing buildings. Christopher Alexander refined his architectural pattern form over 15 years ago, and isolated references to architectural patterns go back hundreds of years. Patterns have taken root in software only recently. Peter Coad noted the link between Alexandrian patterns and software architecture in a CACM article in 1992 Coad 1992. It wasn't until 1993 that patterns began to enter the vernacular as the result of seminars, conference sessions, and journal publications. Drafts of Erich Gamma et al.'s Design Patterns 1995 were widely circulated in 1993 and 1994. This landmark work offered the first comprehensive set of software patterns between two covers, and set new standards for the pattern form. Peter Coad's more recent work has culminated in Object Models: Strategies, Patterns, and Applications Coad 1995. A fledgling body of diverse literature precedes the patterns collected in this volume.
As you examine the contents of the book carefully, you will observe a rich diversity of pattern forms. Some patterns draw on Alexander's style; others draw on the work of Erich Gamma and his colleagues; still others draw on the patterns of Peter Coad; and several are altogether original. We made every effort to preserve the authors' original forms. We avoided tampering with individual expression as much as possible: we made no attempt to enforce a uniform writing style. Although the book lacks the voice of a single author, we wouldn't have it any other way. We hope you join us in celebrating this diversity in the formative stage of a new body of literature.
The chapters in this book are certainly among the most intensely edited works in contemporary software literature. Editing was an ongoing, iterative effort. Before the conference, authors worked with "shepherds" from the patterns community. The goal was for each pattern to contain bare essentials: a clear problem statement, a solution addressing the problem, and a clear statement of forces that motivate the solution. Then, each chapter underwent intensive editing in writers' workshops at the PLoP '94 conference. Authors, reviewers, and other workshop participants discussed the strengths and weaknesses of each paper. Reviewers were encouraged to accentuate the positive and to suggest improvements in content, style, and presentation.
Production editing was also a team effort. Discussions with our colleagues in The Hillside Group steered early editorial decisions. While we focused on the logical organization of the material, our friends at Addison-Wesley created a unified design, swept out passive verbs and dangling prepositions, and richly supported us with logistics, copyright negotiation, and a host of details. Despite our scholarly inclinations to the contrary, page design and formatting contribute greatly to the readability of any written material. Thus, although we received manuscripts in a wide variety of formats, we have tried to integrate them in a single design while preserving the spirit of individual formats.
We simply couldn't have done this without Deborah Lafferty, Penny Stratton, and Tom Stone, who treated this book with the same care and attention as if it were their own. We were proud and pleased--but most of all desparately grateful--to have them on our team.
Finally, we want to emphasize that this book would not have been possible without the talents, hard work, and dedication of the authors. All the copy editing in the world doesn't take the place of high-quality material. We are honored to work in the company of outstanding authors.
Coad92 Coad, Peter. Object-oriented patterns. CACM 35, 9 (Sept. 1992), 152-159.
Coad95 Coad, Peter, with David North and Mark Mayfield. Object Models: Strategies, Patterns, and Applications. Prentice-Hall: c1995.
Gamma95 Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides. Design patterns: Elements of Reusable Object-Oriented Software. Reading, MA: Addison-Wesley, c1995.