What are overlays? Overlays were new with JAS Release 2.0 SR2.00, and further enhanced with Release 2.0 SR2.30DTRA. More properly called “Method Overlays”, they allow the user to define--in the actual scenario data--Smalltalk code which will be used during a simulation run, in the place of the original code. Since the Smalltalk code is organized into modules called “methods”, these allow users to overlay the original method or create new methods.

Overlays can be used to enhance the functional behavior of the simulation, to update instrumentation, to correct a GUI’s function, etc. While they are not useful for more than minor enhancements, overlays provide the advantages of allowing users to:

• Receive “patches” for critical errors from the JAS office more quickly, without waiting for a new release
• Implement behavioral changes particular to a scenario which may not apply to other scenarios
• Investigate new behavior as a prototype to improve future code design
• Conduct testing on the new behavior (Fix-Test-Fix) before integration
• Share their enhancements as easily as sending an email to each other
• Provide enhancements to the JAS office for consideration for integration
• Implement classified algorithms without affecting classification of baseline code
• Create proprietary behavior or algorithms

The primary disadvantages to overlays are:

• You’ve got to be familiar with Smalltalk, or you’ll have difficulty creating overlays and may cause unintended consequences
  • Most users will rely on the JAS office for overlays
    • Users/sites--not the JAS office--are responsible for issues arising from locally developed overlays
  • Users must maintain awareness of what behaviors have been changed via overlay.
• The onus is on the user to maintain, track and update overlays with new releases (if necessary)

What are “HCI” overlays? HCI overlays permit modifying the actual GUIs the modelers use.

Instead of always applying the HCI overlays when opening a scenario, two measures were put in place to allow users to control when to apply HCI modifications: First, the GUI overlays are applied (i.e. usable) only while the Method Source Overlay tool (the “Dynamic Behavior Method Source Overlays” window) is open. It is opened by selecting Tools » Method Source Overlays from within a scenario. Second, either closing the Method Source Overlay Tool or refreshing the scenario will remove the GUI overlay and reinstate the original GUI. Exceptions: Maritime orders GUI overlays and overlay import/export remain applied until the scenario is refreshed.

Note that there is one issue with the SR2.30DTRA image: The presence of GUI overlays causes the simulation run to break. Instead of requiring users to remove all GUI overlays prior to running (which would be a terrible inconvenience), an overlay is available to permit leaving GUI overlays in the scenario during runs.