1. An Introduction to FOM Modules
Björn Möller
Pitch Technologies

2. What Are FOM Modules? The same FOM as before but divided into modules
Support for decoupling the development process for different concerns
Example: RPR platform concerns, sensor concerns, federation management concerns
A way to separate standard FOM concepts from local or temporary adaptations

3. Object & Interaction Roots, Predefined Data Types, etc
The HLAbase FOM Module
Contains
Root classes for Objects and Interactions
Predefined data types (like HLAinteger32BE)
Predefined transportation types, dimensions, etc
MOM
More (Identification, etc)
Automatically loaded by the RTI when Create Federation Execution is called
Guarantees that these concepts are correctly defined
HLAbase
Object & Interaction Roots, Predefined Data Types, etc

4. User Defined FOM Modules
A user defined module can add more classes, interactions, data types, switches, synchronization points, etc
Attributes and parameters can only be added to new object classes and interactions
The first user defined FOM module is known as the primary FOM module (more about this later)
My Object Classes,
Interactions, etc
HLAbase
Object & Interaction Roots, Predefined Data Types, etc

5. Circular Dependencies Not Allowed
Allowed: HLAbase:ObjectRoot - A:Vehicle – B:Aircraft
Disallowed: A:Vehicle – B:Aircraft – A:FreightAirCraft
The ”colon” notation is used here only for clarification

6. Inheritance As Usual
In the FOM HLAbase:ObjectRoot(HLAbase:PrivilegeToDeleteObject) – A:Vehicle (A:Speed, A:Color) – B:Aircraft (B:Altitude)
Available attributes for B:Aircraft
ObjectRoot: PrivilegeToDeleteObject
A:Speed
A:Color
B:Altitude
The ”colon” notation is used here only for clarification

7. Some XML Code (Draft) Extension
<?xml version="1.0" encoding="UTF-8"?>
...
<objects>
<objectClass>
<name>objectRoot</name>
<name>BaseEntity</name>
<name>MyExtensionToRPR</name>
<attribute>
<name>ExtraSpatial</name>
<dataType>SpatialStruct</dataType>
</attribute>
</objectClass>
</objects>
</objectModel>
Extension
XML Namespaces may or may not be used depending on complexity.

8. Impact on OMT Tools
Human
Italian
LifeForm
HLAObjectRoot
Lamborghini
Car
Ferrari
An OMT tool now needs to handle (load, save, visualize, etc) FOMs by module
Example: To be useful an OMT editing tool will need to distinguish between:
A) Is the user adding more items to the currently loaded FOM module, or
B) Is the user adding items to a new FOM module that builds upon some currently loaded FOM module
This is a practical requirement, not a direct requirement by the HLA standard

9. Detailed Semantics for FOM Modules
HLAbase
Primary FOM Module
Additional FOM Module
Identification
Yes
Items starting with HLA
Not allowed
Objects and Attributes
Yes, subclassing
Interactions and Parameters
Data types
Yes, adds
User Supplied Tags
Transportation Types
Dimensions
Time representations
Yes (not used)
Yes, decides
Yes, not used
Synch Points
Switches
Notes

10. How to Use FOM Modules
Local RPR
Extension
Real Time
Reference Platform
(Standard) FOM
My Federation Management
Data Logger Control
HLAbase
Object & Interaction Roots, Predefined Data Types, etc
A Module can add new object and interaction classes,

11. How NOT to Use FOM Modules
My Idea About Aircrafts
Your Idea About Aircrafts
His Idea About Aircrafts
HLAbase
Object & Interaction Roots, Predefined Data Types, etc
Federates still need to agree on how to model the same concept.

12. Interface Specification
CreateFederationExecution(Name, FDDlist)
Takes FDD file list
HLAbase is provided by the RTI
JoinFederationExecution(FedEx, Type, Name, FDD list)
Causes these FOM modules to be loaded unless they already are
DestroyFederationExecution()
Unloads all FOM modules
GetSomeHandle
Can get a handle for any loaded FOM concept
It is recommended to load all FOM modules that your federate refers to. Otherwise a GetHandle may fail.
Handles will never become unavailable since a FOM is never unloaded

13. About FOM Module Loading
HLAbase is loaded implicitly by the RTI
This functionality is required in the RTI and no extra user action is required
The HLAbase file is part of the HLA standard
It is useful to have this file available when developing new FOM modules
One or more FOM modules shall be loaded when the federation execution is created
FOM modules shall always loaded in the specified order to guarentee that dependencies can be resolved
The first module to be (explicitly) loaded is known as the primary FOM module. It provides global settings.
It is a recommended practice to keep track of which your primary FOM module is, for example by providing it first in Create Federation Execution
Additional modules may be loaded later by each joiing federate
Duplicate load of the same module is allowed and void
Modules are never unloaded within a federation execution

14. Backwards Compatibility
If you have exactly one FOM module and load it during create then conceptual backwards compatibility is achieved.
This is useful for example for older federations
Some calls will still need to be modified.
Newer federates can still add new FOM modules later.

15. Life Span of FOM Modules
Once loaded a FOM module will remain available until the federation execution is destroyed
time
My FlightSim
Create Federation
Execution
Local RPR Extension
My Federation Management FOM
RPR FOM
My Fed Mgmt
My Federation Management FOM
Standard RPR Viewer
RPR FOM
HLAbase

16. Required MOM Extensions
The FDD Attribute on ”Federation” will become a list of FDDs
New MOM Interaction per federation HLAreportFOMmoduleLoaded
Provides the name of the loaded module
Will only be sent on load, i.e. the first time a federate joins with that module

17. Impact on RTIs
Main impact is for the ”Join” with additional FOM modules
Likely to require substantial processing on CRCs and every LRC
This may happen during the main execution
Synchronized startup can be used to avoid this
Late joiners means problems anyway...
Load of several FOM modules may be difficult to do in parallell
But will be quick if the module is already loaded
Use a few, large FOMs, not many small ones
Loading FOM modules requires consistency checking