2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Extended FOM Module Merging Capabilities Bjo ̈ rn Mo ̈ ller Andy Bowers Mikael Karlsson Björn Löfstrand

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Outline FOM (actually OMT) background Current FOM merging principles Proposed new capability: Adding attributes to existing classes Proposed new capabiliby: Adding DDM dimensions to existing classes Use case for above: JLVC Discussion: Extending enumerations Conclusions

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 An interesting observation HLA enables us to gradually extend interoperability in a federation without necessarily requiring an update of all federates Adding new object & interaction classes does not require us to update existing systems that have no interest in them. They don’t subscribe. The same applies to adding new attributes The old FOM becomes a subset of the new FOM This is a key HLA feature since federates are often provided by different organizations with different acquisition and update cycles Also facilitates the use of COTS/GOTS tools

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Evolution of the HLA Object Model Template HLA 1.3 HLA HLA BNF Format Monolithic OMT and FED file XML Based (DTD) Monolithic Single file XML Based (Schema) Modular or Monolithic Extendable

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 FOM Module Merging Principles SpeedInteger ColorEnum FuelFloat ColorEnum Module M1Module M2 FuelFloat ColorEnum RESULT SpeedInteger In most cases the Union operation is used Example from merging data type tables:

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Merging Sibling Classes Module M1 Module M2 RESULT

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Merging Subclasses Module M1 Module M2 RESULT S caffolding definition

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 HLA Attribute Merge A new module cannot add attributes to an already defined class Need to add new attributes in a subclass Module M1 Module M2 S caffolding definition

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 When is this a problem? An older federate already registers object instances using the initial class (without extra attributes) Example: PhysicalEntity.Platform.Aircraft We want to add more attributes to the Aircraft class or even to a superclass like PhysicalEntity Cannot add attributes using a new FOM Module Need to modify the original FOM, that is a Reference FOM Problem: We end up with a non-standard version of the FOM module FORK!

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Proposed New Attribute Merge Module M1 Module M2 RESULT New! FOM Modules can add more attributes to existing classes!

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Impact of the proposal Does not affect current federations, federates, FOM and federation agreement The FOM merge (siblings and subclasses) is a subset of the new proposed merge. Impacts the RTI Some design discussions remain for the HLA interface specification. What happens to already registered instances of a class when a new FOM module is merged and new attributes are added? At least three solutions are possible

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Short-term workaround Perform this merge at development time using a special, non- standard mode of an OMT tool Provide the already merged modules as a monolithic FOM at Create Federation Execution Module M1 Module M2 RESULT

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Attribute and DDM recap

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Merging DDM Dimensions As federation size grows, there is an increased need to filter updates and interactions using HLA DDM Example: Using the dimensions “Lat”, “Long” and “Side” enables us to subscribe only to updates from opposing platforms in a certain geographical area Same problem again: Cannot add new dimensions to an attribute in one FOM module using another FOM module Need to modify original FOM module, which is undesirable if this is a reference FOM

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Proposed New Dimension Merge Allow new FOM Modules to add new Dimensions to existing Attributes and Interaction classes Does not affect current federations, federates, FOM and federation agreement The FOM merge is a subset of the new proposed merge No major challenges for the RTI

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 A Bolder Proposal for DDM Remove the Dimensions property of attributes and interactions. Allow any dimension in the FOM to be used when subscribing to and sending interactions. Allow any dimension in the FOM to be used when subscribing to and updating attributes.

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Use Case: JLVC The United States Joint Staff Deputy Director J7 (JS DD J7), formerly the Joint Forces Command (JFCOM) J7, sponsors the development and use of the Joint Live, Virtual, Constructive (JLVC) Federation JLVC is a RPR FOMv2d17-based federation JLVC FOM has diverged significantly from the RPR FOM Long-term goal is to use standard RPR FOM plus modular extensions When studying migration from HLA 1.3 to a “mixed-mode” federation was developed and the FOM was migrated to the modular format

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 JLVC Experiences Tried to maintain unmodified RPR FOM and put extensions in a subclass in a new module Platform.Aircraft.JLVC_Aircraft Issue 1: Still needed to add DDM dimensions to attributes in the original superclasses in the RPR FOM Issue 2: Existing HLA 1.3 federates did not use/recognize the new subclasses Also some RTI specific issues with respect to attribute ordering

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Related discussion: Enumerations How to maintain large and growing enumerations? Two proposed solutions Put enumerated data type(s) in a separate module Start supporting “Xinclude” statement in the OMT XML format. Store enumerators separately. The first solution is already supported by HLA Evolved and is now introduced in the RPR FOM Another question: Should a new FOM module be able to extend an already defined enumeration? This may break older federates Nothing proposed for now

2013 Spring Simulation Interoperability Workshop 13S-SIW-004 Conclusions Two extensions to the FOM merging of HLA are proposed: Allow the addition of new attributes to an existing object class using a new FOM module. Allow the addition of new dimensions to an existing attribute or interaction class using a new FOM module. One of the main drivers for these extensions is the use of reference FOMs. A practical use case is presented to support this Enumerations have also been discussed. A useful approach for extending them already exists