An empirical assessment of the software design pattern concept

Context: The publication of the milestone textbook on design patterns by the ‘Gang of Four’ (GoF ) in 1995, introduced a set of 23 design patterns that are largely concerned with improving the practices and products of software development. However, there has been no comprehensive assessment of the effectiveness of design patterns, nor is there any evidence about any claims and factors that are made for pattern reuse in software development. Aims: The aims of this thesis are to assess the design patterns systematically in a sequence of studies, and to identify the claims and factors to determine how well they reflect experiences of pattern reuse in practice. Method: This thesis describes four studies: a document survey to identify claims for patterns, a mapping study to identify empirical studies about patterns, an online survey, and a narrative synthesis. The mapping study and the online survey together provide quite comprehensive and thorough evidence for the narrative synthesis. In the narrative synthesis, we check whether there is any consistency or not in the evidence about specific patterns, and also to see how the claims and factors influence pattern reuse. Results: The mapping study found 20 primary studies, and the online survey had 206 usable responses. In the 20 primary study of the mapping study 17 design patterns were examined. In the online survey 175 respondents considered patterns were useful, and 155 respondents reported on patterns that they considered not to be useful. Conclusion: From the synthesis results, the specific patterns Composite and Observer are evaluated as being generally useful, but the Visitor and Singleton patterns, while useful, have possible negative aspects. And also four of the claims and the effect of one factor are demonstrated to be generally true. But the others are either unsupported or have no effect.