================================================================================ P9422 R.N. Bol, J.W.C. Koorn, L.H. Oei & S.F.M. van Vlijmen "Syntax and static semantics of the interlocking design and application language" An interlocking is a system used at railway yards for guaranteeing safety of train movements. This report opens a series of studies on tightly related specification languages for interlockings. These languages together are called ISL: Interlocking Specification Language. ISL is designed by P. Middelraad of the Dutch railway company, NS, de Nederlandse Spoorwegen. NS have developed a symbolic intermediate tool interface language, IDEAL, for ISL. IDEAL is the Interlingua for all men and machines using ISL. This report introduces interlockings, the long-term goals of the ISL project, and, as a first step, we present the syntax and static semantics of IDEAL in ASF+SDF, an algebraic specification formalism. Several improvements of IDEAL are suggested.