KBQA: Learning Question Answering over QA Corpora and Knowledge Bases
Table 4: valid(k)
['k', '1', '2', '3']
Specifically, we select top 17,000 entities from the RDF knowledge base K ordered by their frequencies. The frequency of an entity e is defined as the number of (s,p,o) triples in K so that e=s. We choose these entities because they have richer facts, and therefore are more trustworthy. Then, for each k, we count the number of these (s,p+,o) that can find its corresponding SPO triples in Wikipedia Infobox. More formally, let E be the sampled entity set, and SPOk be ( s,P+,o)∈K with length k. We define valid(k) to measure the influence of k in finding meaningful relations as follows: valid(k)=∑s∈E|{(s,p+,o)|(s,p+,o)∈SPOk,∃p,(s,p,o)∈Infobox}| (29) Note that for expanded predicates with length ≥2, we only consider those which end with name. This is because we found entities and values connected by other expanded predicates always have some very weak relations and should be discarded. The number of valid expanded predicates significantly drops when k=3. This suggests that most meaningful facts are represented within this length. So we choose k=3 in this paper.