progid

ProgID, short for Programmatic Identifier, is a human-readable string used in Component Object Model (COM) to identify a class object. It provides an abstraction over the underlying CLSID (a GUID), allowing client applications to instantiate COM components without needing to know the exact GUID. ProgIDs are registered in the Windows registry and are resolved by the COM runtime to the corresponding CLSID.

Registry representation and structure: In the registry, a ProgID is registered under HKEY_CLASSES_ROOT (HKCR) with a key named after the ProgID. The ProgID key typically contains a mapping to the CLSID of the class, commonly via a CLSID value or a nested CLSID subkey. The CLSID key, found under HKCR\CLSID\{GUID}, stores details about the server, such as InprocServer32 or LocalServer32, which indicate how the component is loaded. Some ProgIDs also participate in versioning, using a VersionIndependentProgID or CurVer mappings to point to the appropriate versioned ProgID.

Resolution and usage: Clients create objects by referencing the ProgID, for example through languages that interoperate with COM (such as VBScript, VBA, or .NET via Type.GetTypeFromProgID). The runtime translates the ProgID to the corresponding CLSID and then calls CoCreateInstance to instantiate the object. If the ProgID is not registered or the underlying server is unavailable, object creation fails.

Versioning and examples: COM often uses versioned ProgIDs to distinguish major revisions, with a VersionIndependentProgID providing a stable alias that maps to the current version. Common examples include "Excel.Application" and "Scripting.FileSystemObject." The reliability of ProgIDs depends on correct registration and maintenance of the registry and COM servers.

See also: CLSID, COM, Windows Registry.