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A developer attempting to evolve a system in which design patterns have been applied can benefit from knowing which code implements which design pattern. For instance, the developer may be able to understand the purpose, or to assess the flexibility of the code, more quickly. The degree to which the developer benefits depends upon their understanding of the pattern. Achieving an in-depth understanding of even a simple pattern can be difficult as pattern descriptions span several pages of text, and discuss interrelated design concepts and choices. To enable a developer to effectively trace the design goals associated with a pattern to and from source, we have developed the Design Pattern Rationale Graph (DPRG) approach and associated tool. A DPRG makes explicit the relationships between design concepts in a design pattern, provides a graphical representation of the design pattern text, and supports the linking of those concepts to implementing code. In this paper, we introduce the DPRG approach and tool, and present case studies to show that a DPRG can, at low-cost, help a developer identify design goals in a pattern, and can improve a developer's confidence about how those goals are realized in a code base.