In order for ABL to identify any .NET class or other .NET type you reference, it has to locate the .NET assembly that contains the type definition. In .NET, an assembly is a kind of Windows dynamic link library (DLL) that is specially formatted to uniquely identify the .NET types that it defines. For some supported .NET types, ABL internally knows how to locate the assemblies that define them. For any additional .NET types you want to reference, you must identify the assemblies that define them to ABL using an assembly references file. This is an XML file that you can edit using an OpenEdge tool to record the name and identification information for each additional assembly that you require for your application. For more information on assembly references files and how to use them, see Identify .NET assemblies to ABL.