  Learning representations for semantic relations is important for various
tasks such as analogy detection, relational search, and relation
classification. Although there have been several proposals for learning
representations for individual words, learning word representations that
explicitly capture the semantic relations between words remains under
developed. We propose an unsupervised method for learning vector
representations for words such that the learnt representations are sensitive to
the semantic relations that exist between two words. First, we extract lexical
patterns from the co-occurrence contexts of two words in a corpus to represent
the semantic relations that exist between those two words. Second, we represent
a lexical pattern as the weighted sum of the representations of the words that
co-occur with that lexical pattern. Third, we train a binary classifier to
detect relationally similar vs. non-similar lexical pattern pairs. The proposed
method is unsupervised in the sense that the lexical pattern pairs we use as
train data are automatically sampled from a corpus, without requiring any
manual intervention. Our proposed method statistically significantly
outperforms the current state-of-the-art word representations on three
benchmark datasets for proportional analogy detection, demonstrating its
ability to accurately capture the semantic relations among words.
