1. A method of searching a database retained in a data repository, comprising: receiving a mixed query that comprises a regular expression and a semantic constraint, wherein the regular expression is a pattern of elements, and wherein the elements in the regular expression comprise: a first wildcard, wherein the semantic constraint restricts a meaning of the first wildcard in the regular expression; and at least one of an explicit lexical constraint or a second wildcard; and utilizing at least one processor on at least one computing device, executing the mixed query to retrieve results that match the pattern of the elements in the regular expression and satisfy the semantic constraint, wherein the results are retrieved from the database retained in the data repository.