  Hashtag annotation for microblog posts has been recently formulated as a
sequence generation problem to handle emerging hashtags that are unseen in the
training set. The state-of-the-art method leverages conversations initiated by
posts to enrich contextual information for the short posts. However, it is
unrealistic to assume the existence of conversations before the hashtag
annotation itself. Therefore, we propose to leverage news articles published
before the microblog post to generate hashtags following a Retriever-Generator
framework. Extensive experiments on English Twitter datasets demonstrate
superior performance and significant advantages of leveraging news articles to
generate hashtags.
