Language understanding has been well studied in the context of question/answering (Harabagiu and Hickl, 2006;Liang et al., 2011), entailment (Sammons et al., 2010), summarization (Hovy et al., 2005;Daumé-III and Marcu, 2006), spoken language understanding (Tur and Mori, 2011;Dinarelli et al., 2009), query understanding (Popescu et al., 2010;Li, 2010;Reisinger and Pasca, 2011), etc.
data sources in VPA systems pose new challenges, such as variability and ambiguities in natural language, or short utterances that rarely contain contextual information, etc.