Klein (1998) breaks the development of simulation into two basic types.  In the Monolithic design technique, all relevant information about the model is kept in the model itself.  These systems are usually built from scratch and do not share the components that comprise them.  The decline of this model occurred in the mid 1990’s when the Administration lowered Defense Department budgets.  There became a need for greater efficiency in the creation of the simulation software.
	The distributed model breaks the total model into a set of sub-models.  These sub-models can be interchanged between systems to lower total development costs.  High Level Architecture was developed by the US Department of Defense and is an upcoming IEE simulation interoperability standard.
	Under this standard, HLA defines the behavior of the overall distributed model, called a Federation, and the component pieces, called Federates.  The infrastructure specification details how the Federates communicate through the Runtime Interface (RTI).  Finally, the Object Model Template (OMT) defines the documentation process for Federations and Federates.