Each data entry in the metabase is assigned a unique identifier, a DWORD containing a number that uniquely identifies the entry. Identifiers used by IIS are assigned from a pool of reserved numbers. If you create identifiers in the metabase, use identifier numbers greater than 65535 (0x0000ffff) to avoid conflicts with current or future system data.
Each identifier is also assigned a user type, which is a DWORD that specifies how the data is used. Current IIS user types include:
User types enable you to classify your identifiers by application. You must assign a user type to each identifier you create in the metabase, although each identifier is not required to have a unique user type. The numbers from 0 to 2,000 are reserved for current and future system user types, so be sure to use a number greater than 2,000.
You can use the user type to filter data requested from a key. For example, the GetAllData method has a parameter, dwUserType, you can use to specify that only data of a certain user type is to be returned. For example, if this parameter is set to IIS_MD_UT_SERVER during the method call, only data related to the server will be returned.
Note Metabase identifiers must be unique, but multiple identifiers can have the same user type and data type. The first 32K of the DWORD is reserved by the system for IIS data; the remainder is reserved for Microsoft® FrontPage® data.