Table 1 Terminals used by our GP-based image retrieval framework

tf

Raw term frequency (number of times a term occurs in a document)

idf

Inverse document frequency given by \(\log (1 + \frac{N}{df}), N\) is number of documents in the corpus and \(df\) is number of documents where the term \(t\) appears

\({\text{ tf}}*{\text{ idf}}\)

tf-idf weighting scheme

avgdl

Average document length

\(bm25\)

Okapi BM25 ranking formula (see Eq. 5)

norm

Document length