"Design Patterns", by Erich Gamma, Richard Helm, Ralph Johnson, and John
Vlissides, was released in October, 1994. It has continued to sell for 20
years and has had a big impact. Twenty years after it came out, some of
the patterns continue to be important, some less important. New patterns
have arisen that have displaced some of the older patterns. There are
common ways that the patterns are misused. Ralph Johnson will talk about
what he has learned about the patterns since the book was published.

*Bio:* Ralph Johnson is one of four coauthors of "Design Patterns" and the
leader of the group that built the first refactoring tool, the Smalltalk
Refactoring Browser. He is still working on patterns and program
transformation, though the spotlight has shifted off of basic
object-oriented design to topics like parallel programming and innovative
ways of making business software.

He joined the Department of Computer Science at the University of Illinois
at Urbana-Champaign in 1985, and retired recently to work on a system for
automating business transactions.