A methodology for specifying concurrent systems is presented. A model of computation for concurrent systems is presented first. The syntax and semantics of the language CRYSTAL are introduced. The specification of a system is called a space-time algorithm since space and time are explicit parameters in the description. Fixed-point semantics is used for abstracting the behavior of a system from its implementation. The consistency between an implementation and its description can therefore be ensured using this method. Formal semantics for an arbitrary transistor network is given. An "interpreter" for space-time algorithms -- a hierarchical simulator -- for VLSI systems is presented. The framework can be viewed as a concurrent programming notation when describing communicating processes and as a hardware description notation when specifying integrated circuits.
