NOMAD was released before these industry events, and thus, like System R, NOMAD drew on earlier academic work by relational database pioneers such as E. F. Codd. Early NOMAD development was in particular inspired by Christopher J. Date's influential "An Introduction to Database Systems", itself first published in 1975. This book had technical ideas about the relational database model, and included a brief mention of SEQUEL (later SQL). Later editions of the book included NOMAD itself, and Date's approval of NOMAD's support of the relational database model.