Enumerations

All of the fields in DIS messages contain binary, numeric fields. However the fields are often not quantitative. Instead a field is often used for identity. For example a field in all Protocol Data Units (PDUs) also contain a field that describes what type of PDU this is.

PDU Type	Field Value
Entity State	1
Fire	2
Detonation	3
Collision	4

But why did a DIS simulation agreed to this? Obviously, they should, because we want to handle decoding the incoming message correctly.

We also want to handle object types correctly as well. Does this message internally refer to a Russian T-72 tank or a US M-114 155mm howitzer? This is done with a set of enumeration values in a record. The US howitzer record looks like this:

Kind	Domain	Country	Category	Subcategory	Specific
1	1	225	1	3

When we encounter these values in a PDU in the field we know we are talking about an M1A2 tank. Likewise, a T-72 tank in the same type of PDU would look like this:

Kind	Domain	Country	Category	Subcategory	Specific
1	1	222	1	2	12

This identifies a Russian T-72 tank with mine plows. There's nothing that makes 222 inherently Russian, nor anything that makes 225 American. The numbers are arbitrary, but everyone should agree on the semantic value in this context and in this record.

What would be terrible is having all participants in a simulation agree to new semantics for every simulation. We want a pre-established set of enumerated values.

SISO has worked on this problem by creating and maintaining the lists of arbitrary numbers. The nature of the world is such that it may, over a short period, add new vehicles or weapons. But the definition of the DIS protocol is approved by IEEE, and it may take years to approve a standard of that nature. SISO defined the "Reference for Enumerations for Simulation Interoperability", a document that can be relatively easily updated.

An example of this document is named SISO-REF-010, and are available at SISO