DEVS and HLA: Complementary paradigms for modeling and simulation?

The HLA represents a major advance in M&S methodology as a standard mandated by the U.S. Department of Defense (DoD) to promote simulation interoperability and reuse. However, as currently formulated for acceptance as an IEEE standard, it standardizes certain aspects of the M&S process while leaving others unspecified. On the other hand, the Discrete Event System Specification (DEVS) methodology has been under development since the '70s and formalizes certain aspects of the M&S process while not addressing others. In this paper, we critically examine the current state of both the HLA and DEVS specifications. We point out the strengths and limits/omissions of each. We pose the question to each: Are the limits and omissions appropriate at this stage of development or do they represent more fundamental limitations that constitute a barrier to future development? Particularly, since it has the power of mandate, any fundamental limitations on HLA might lead to de facto non-acceptance of the standard with negative consequences on the course of M&S methodology. We argue that the limits of each are indeed critical limitations but that a combination of HLA and DEVS can better overcome these barriers to widespread adoption than can either alone. Finally, we suggest a roadmap for such a combination and point out the possibilities for employing it in such expanding initiatives as Simulation-Based Acquisition.