DIS-XML: Moving DIS to Open Data Exchange Standards

The Distributed Interactive Simulation (DIS) IEEE-1278.1 standard is used in many military simulations. The binary data format for DIS does not lend itself to use in emerging web services standards or data analysis and storage tools because the data format is not recognized by most general purpose data manipulation tools. We examine an alternate XML-based representation of DIS information. An XML representation unlocks legacy data by placing it in a standard data format, and thereby integrates with the many XML data transformation, storage, and analysis tools. An XML-based approach also allows easy generation of programming language Application Program Interfaces (APIs). The information contained in DIS PDUs can shift between any of several representations, including the binary IEEE1278.1 standard, XML, or programming language objects. The XML representation can be used in web services applications or passed over instant messaging channels. Initial tests demonstrate satisfactory performance. 1. Overview and Motivation Distributed Interactive Simulation (DIS) [1] is a communications protocol standard used in many military simulations, including large-scale High Level Architecture (HLA) federations through network bridges commonly called DIS gateways. The protocol defines, among other things, a set of Protocol Data Units (PDUs). The PDUs are specified in a binary format to promote efficiency. A single host may process thousands of PDUs per second, and binary formats are a more efficient format from which to extract information. The greater efficiency comes at a cost. Because the data is in a binary format it cannot be easily processed by tools that are unaware of the DIS standard. For example, it might be useful to search an archive of all PDUs exchanged in an exercise in order to find entities that passed through a particular area or that meet some other criteria. If the archived PDUs are in the binary DIS format this task is more difficult than it needs to be; the tools that search the PDU archive need to understand the IEEE standard format. It would be more useful to reuse powerful, industry standard tools to process the information, but these tools typically do not understand the binary DIS format. Many DIS implementations read DIS PDUs from the network and transform them into programming language objects [2] [3]. Within the context of the simulation programming logic the PDUs are more easily handled as objects, typically with accessor methods to retrieve individual PDU fields. Users may modify the field values and then write the PDU back to the network in IEEE1278.1 format. The process of changing between object and binary PDU format and back again is called marshalling and unmarshalling, or sometimes serialization and deserialization. The information contained in the two representations of the PDU is essentially identical, and differ only in format. This presents one possible avenue for tool-based processing of DIS information: the programming language objects. But this approach is ultimately unsatisfactory, for the same reason that the binary DIS format is problematic: the tools need to understand the programming Application Program Interface (API), and in general this is unlikely to be the case for third-party tools. What is needed is a format that can both represent the information in a PDU and be used by other tools, all without giving up the performance and backwards compatibility advantages of the IEEE-1278.1 binary format or the programming convenience of an object-based API. The Extensible Markup Language (XML) [4] is a natural choice to meet these requirements.