  DEVS is a popular formalism to model system behaviour using a discrete-event
abstraction. The main advantages of DEVS are its rigourous and precise
specification, as well as its support for modular, hierarchical construction of
models. DEVS frequently serves as a simulation "assembly language" to which
models in other formalisms are translated, either giving meaning to new
(domain-specific) languages, or reproducing semantics of existing languages.
Despite this rigourous definition of its syntax and semantics, initialization
of DEVS models is left unspecified in both the Classic and Parallel DEVS
formalism definition. In this paper, we extend the DEVS formalism by including
an initial total state. Extensions to syntax as well as denotational (closure
under coupling) and operational semantics (abstract simulator) are presented.
The extension is applicable to both main variants of the DEVS formalism. Our
extension is such that it adds to, but does not alter the original
specification. All changes are illustrated by means of a traffic light example.
