A computer generates semantic structure information from a document. The semantic structure information includes a plurality of semantic structures in a plurality of sentences in the document and a plurality of morphemes included in each of the plurality of sentences belong to a corresponding semantic structure. The computer generates a plurality of codes by encoding the plurality of morphemes for each of the plurality of sentences. The computer specifies a specific code that corresponds to a specific morpheme from among the plurality of morphemes included in each of the plurality of sentences, wherein at least one morpheme is potentially missing in a semantic structure that the specific morpheme belongs to. A missing-portion information indicates the missing morpheme is included in a prior sentence in the document. The computer adds missing-portion information to the specific code for each of the plurality of sentences.