subscribing to object class attributes and interactions. Regions are also used when sending attribute updates and interactions. When DDM is used, attribute updates and interactions will only be delivered if there is a region overlap. Key services for Regions are: CreateRegion that is used to create a region with a specified set of Dimensions. DeleteRegion that is used to delete a region. CommitRegionModifications that is used to change the ranges of a dimension for a Region. Key services for exchanging attribute updates with DDM are: RegisterObjectInstanceWithRegions that is used to register an object instance with regions associated with its attributes. AssociateRegionsForUpdates that is used to associate regions with attributes of an object instance. SubscribeObjectClassAttributesWithRegions that is used to subscribing to attributes of objects where the regions used for subscription overlaps with the regions of the attributes. Key services for exchanging interactions with DDM are: SubscribeInteractionClassWithRegions that is used to subscribe to interactions where the regions used for subscription overlaps with the regions of the interactions. SendInteractionsWithRegions that is used to send interactions with associated regions. Support services The HLA Support Services, described in chapter 10 of the HLA Interface Specification, provide a number of supporting services. These include: Getting Handles (references) to be used in the above service calls. Setting various runtime switches, in particular for advisories (notifications). Controlling the delivery of callbacks. Management Object Model The purpose of the Management Object Model, described in chapter 11 of the HLA Interface Specification, is to provide services for managing a federation. This is performed using the MOM object and interaction classes. MOM objects are defined in a special FOM module called the MIM, that is automatically loaded by the RTI. Key MOM features include: List and inspect properties of federates. Inspect properties of the federation. Get the content of the current FOM and FOM modules. Inspect the state of Time management. Inspect and modify publications and subscriptions of federates. Inspect certain performance figures. Inspect which federate that calls which HLA services. Inspect status of synchronization points. Object model template (OMT) The OMT is a template used for describing Federation Object Models (FOMs) and Simulation Object Models (SOMs). FOMs and SOMs can be represented in a tabular format or using XML. The latter format is used when a FOM is loaded into the RTI. In earlier versions of HLA, FOMs were monolithic, but the current version of the standard supports modular FOMs,