During the COM era, identification and mapping of interfaces was driven by unique identification numbers, known as globally unique identifiers (GUIDs). Although this is just one of the many uses of GUIDs, COM definitely is the one that jumps immediately to mind.
For COM interoperability as well as other uses, the .NET Framework has a struct to represent such identifiers:
System.Guid. A GUID is basically nothing more than a “very random” 128-bit integer that has a global uniqueness property. Global in this context means that there’s a very low likelihood of two generated GUIDs (no matter where and when that happens) being the same. For that reason, it’s safe to generate a GUID for some use (for example, to identify a COM interface) ...