  A code change pattern represents a kind of recurrent modification in
software. For instance, a known code change pattern consists of the change of
the conditional expression of an if statement. Previous work has identified
different change patterns. Complementary to the identification and definition
of change patterns, the automatic extraction of pattern instances is essential
to measure their empirical importance. For example, it enables one to count and
compare the number of conditional expression changes in the history of
different projects. In this paper we present a novel approach for search
patterns instances from software history. Our technique is based on the
analysis of Abstract Syntax Trees (AST) files within a given commit. We
validate our approach by counting instances of 18 change patterns in 6
open-source Java projects.
