For simulations that are to enable human understanding of the simulated system, inspectable models are highly desirable. A model is inspectable to the extent that its observer can access and interpret each of its reasoning steps. Development of an inspectable model requires an architecture that represents explicitly some of the key types of relationships among domain objects. Although there are formalisms that address some of these relationships, none attempts a representation for a dynamic simulation that is both comprehensive and general. This paper defines an architecture that meets these requirements for well-defined, engineered systems. The architecture combines features from two formalisms, namely, discrete event simulation modeling, and functional representation. Besides representing generalization-specialization and multi-level part-whole composition in a dynamic world, we provide an explicit representation for causality and functionality. We set up a framework for developing well-integrated systems, and an architecture for the core components of a `shell.' We use a complex but sparse class structure that allows for composition of elementary units into structures of arbitrary complexity. Our architecture is event-driven, but uses a distributed timing mechanism. The scope of our research includes definition of the problem and the solution method. Implementation of a prototype to validate key aspects of the architecture is in progress. We have named the architecture `IDEA' for inspectable discrete event architecture.