Design Patterns:Elements of Rousable Object-Oriented Software Foreword Consider the work of a future software archeologist,tracingthe history of computing.The tossil record will likely show clearstrata:here is a layer formed of assembly language artifacts,there is a layer populated with the skeletons of high orderprogramming languages (with certain calcified legacy partsprobably still showing aome aigns of life).Each auch layer willbe intersected with the imprint of other factors that have shapedthe software landscape:components residue from the greatoperating system and browser wars,methods,processes,toolg Eachline in this strata marks a definitive event:below that line,computing was this way;above that line,the art of computing hadchanged Deaign Patterns draws auch a line of demarcationithis is a work that repr in the practice ofcomputing. Erich,Richard, and John presen a compellingcase for the importance of patterns in crafting complex systems.Additionally,they give us a language of common patterns that canbe used in a variety of domains. The impact of this work cannot be overstated.As I travel aboutthe world working with projects of varying domains andcomplexities,it is uncomon for me to encounter de not at t heard of the e patterns mo In the moresuccessful projects,it is quite common to see many of thesedesign patterns actually used. With this book,the Gang of Four have made a seminalcontribution to software engineering.There is much to learnedfrom them,and much to be actively applied. Grady Booch Chief Scientist,Rational Software CorporationDesign Patterns: Elements of Reusable Object-Oriented Software 9 Foreword Consider the work of a future software archeologist, tracingthe history of computing. The fossil record will likely show clearstrata: here is a layer formed of assembly language artifacts,there is a layer populated with the skeletons of high orderprogramming languages (with certain calcified legacy partsprobably still showing some signs of life). Each such layer willbe intersected with the imprint of other factors that have shapedthe software landscape: components, residue from the greatoperating system and browser wars, methods, processes, tools. Eachline in this strata marks a definitive event: below that line,computing was this way; above that line, the art of computing hadchanged. Design Patterns draws such a line of demarcation;this is a work that represents a change in the practice ofcomputing. Erich, Richard, Ralph, and John present a compellingcase for the importance of patterns in crafting complex systems.Additionally, they give us a language of common patterns that canbe used in a variety of domains. The impact of this work cannot be overstated. As I travel aboutthe world working with projects of varying domains andcomplexities, it is uncommon for me to encounter developers whohave not at least heard of the patterns movement. In the moresuccessful projects, it is quite common to see many of thesedesign patterns actually used. With this book, the Gang of Four have made a seminalcontribution to software engineering. There is much to learnedfrom them, and much to be actively applied. Grady Booch Chief Scientist, Rational Software Corporation