Abstract: A semantic relational database has a phrase registry data store of definitions and data handlers that syntactically traverse sentences and report word phrases of relationships defined by the sentences. In some aspects, the database has a sentence data structure in which a sentence refers to another sentence by containing a sentence phrase definition for the other sentence. In other aspects, the database has a sub-sentence data structure that stores sentences as sub-sentences having syntax types specified by a syntax type data structure. A modified relationship is obtained by one sub-sentence being designated to modify another sub-sentence of the same sentence.