explicitly provide this capability. It is worth noting that this capability was a major driving force in the development of OMAR and the MIDAS redesign.

Most of the architectures have been implemented on one or only a few computer platforms. COGNET and OMAR are more flexible, and Micro Saint and Soar are available for almost any platform a user could require.

For those users needing to modify the architectures to fit the needs of their applications, the language in which the architectures are written is of some concern. To many military simulation modelers who have done most of their work in FORTRAN and C, architectures such as ACT-R, EPIC, and OMAR (written in Lisp) may pose some (small) problems.

The software provided to assist the modeler in creating models in the various architectures ranges widely. At one extreme is EPIC, for which there exists very little such software; at the other extreme is OMAR, whose toolkit appears well thought out and tailored to the user not intimately familiar with OMAR's inner workings. To their credit, though, ACT-R and Soar both have a very large base of users, many of whom have developed additional tools to facilitate the use of the two systems.

Some of the architectures are too new for any substantive validation to have been done. In other cases (e.g., HOS), certain submodels have been extensively validated. Some of the architectures have been validated in their entirety ("full model" validation in Table 3.1), some of these extensively. At least one (Micro Saint) has instances that have received military accreditation. Unfortunately, most of the validation of "full models" has been based on subjective assessments of subject matter experts, not real human performance data. This last consideration dictates considerable caution on the part of users.

As discussed above, the various architectures have different strengths and