  Idiomatic expressions like `out of the woods' and `up the ante' present a
range of difficulties for natural language processing applications. We present
work on the annotation and extraction of what we term potentially idiomatic
expressions (PIEs), a subclass of multiword expressions covering both literal
and non-literal uses of idiomatic expressions. Existing corpora of PIEs are
small and have limited coverage of different PIE types, which hampers research.
To further progress on the extraction and disambiguation of potentially
idiomatic expressions, larger corpora of PIEs are required. In addition, larger
corpora are a potential source for valuable linguistic insights into idiomatic
expressions and their variability. We propose automatic tools to facilitate the
building of larger PIE corpora, by investigating the feasibility of using
dictionary-based extraction of PIEs as a pre-extraction tool for English. We do
this by assessing the reliability and coverage of idiom dictionaries, the
annotation of a PIE corpus, and the automatic extraction of PIEs from a large
corpus. Results show that combinations of dictionaries are a reliable source of
idiomatic expressions, that PIEs can be annotated with a high reliability
(0.74-0.91 Fleiss' Kappa), and that parse-based PIE extraction yields highly
accurate performance (88% F1-score). Combining complementary PIE extraction
methods increases reliability further, to over 92% F1-score. Moreover, the
extraction method presented here could be extended to other types of multiword
expressions and to other languages, given that sufficient NLP tools are
available.
