Identifying and exploiting target entity type information for ad hoc entity retrieval

Abstract

Today, the practice of returning entities from a knowledge base in response to search queries has become widespread. One of the distinctive characteristics of entities is that they are typed, i.e., assigned to some hierarchically organized type system (type taxonomy). The primary objective of this paper is to gain a better understanding of how entity type information can be utilized in entity retrieval. We perform this investigation in two settings: firstly, in an idealized “oracle” setting, assuming that we know the distribution of target types of the relevant entities for a given query; and secondly, in a realistic scenario, where target entity types are identified automatically based on the keyword query. We perform a thorough analysis of three main aspects: (i) the choice of type taxonomy, (ii) the representation of hierarchical type information, and (iii) the combination of type-based and term-based similarity in the retrieval model. Using a standard entity search test collection based on DBpedia, we show that type information can significantly and substantially improve retrieval performance, yielding up to 67% relative improvement in terms of NDCG@10 over a strong text-only baseline in an oracle setting. We further show that using automatic target type detection, we can outperform the text-only baseline by 44% in terms of NDCG@10. This is as good as, and sometimes even better than, what is attainable by using explicit target type information provided by humans. These results indicate that identifying target entity types of queries is challenging even for humans and attests to the effectiveness of our proposed automatic approach.