- Enumerations for Simulation Interoperability. The Reference document is updated regularly. It specifies numerical values and associated definitions for fields that are identified as enumerations in SISO Standards Products and SISO-sponsored standards published by IEEE for High Level Architecture (HLA) and Distributed Interactive Simulation (DIS). Defines a consistent schema and repository for enumerations for distributed simulation. Enumerations for simulations may be applied in other architectures to HLA and DIS such as the Test and Training Enabling Architecture (TENA).