Gister-CL can be used to help automate the above process. In practice, it may not be possible to know and assess characteristics of even friendly, much less enemy, forces. For example, assessing characteristics like morale, readiness, and tradition is a highly subjective process. Thus, it may be difficult to give a precise FM value, so a range is given instead. Furthermore, one may be uncertain about any assessment of a FM they might wish to express. Consequently, evidential reasoning is important for selecting an appropriate unit.
Unit selection involves first comparing the perceived strength of friendly and potential enemy forces, then selecting a unit based on the degree to which a unit meets or exceeds prespecified strength-ratio requirements. Accomplishing this within an ER framework requires constructing frames of discernment and relationships between them for both friendly and enemy unit forces. A frame is constructed that represents the nominal ``base'' strength for each unit, and other constructed frames represent the FM assessments of other force characteristics. Within Gister-CL, these frames are constructed in a gallery as shown in Figure 2. Frames corresponding to a friendly force begin with ``F", and frames corresponding to an enemy force begin with an ``E".
Figure 2: Gister gallery for Army unit selection
Relationships between the frames are represented by connecting arcs called compatibility relations (CRs), which compute the result of combining frames. In our example, CRs are often multiplicative. However, some are not. For example, the relative firepower of a unit depends on the relative values of its constituent TROOPS and ARMAMENT FM values. The RELATIVE FIREPOWER FM value is, in our implementation, the maximum as opposed to the product of the FM values in the TROOPS and ARMAMENT frames. The reason for this dependence is that even if a unit does not have its full complement of troops, the remaining troops may have sufficient armament to balance deficiencies in troops. Conversely, a unit may have sufficient troops to balance deficiencies in armament.
Figure 3: Result of degree to which unit meets force ratio requirements.
Given a set of FMs for a subset of friendly and enemy characteristics, a Gister-CL analysis is used to reason about the characteristics and come to a conclusion about each unit. For example, an analysis of the characteristics of a particular unit for a deterrent mission against a particular enemy force results in the distribution shown in Figure 3.