Metadata is data that describes other data. It is important in applications that need the ability to identify and possibly adjust to changes in the backend data store.
In ADO.NET, metadata is exposed through the DbConnection object's GetSchema method, which you can call with no parameters to get a metadata collection list.
The GetSchema method contains an overload that accepts a collection name, such as Tables or Databases.
You can use a GetSchema overload that accepts a collection name and an array of restriction filter strings to narrow the scope of the returned data.
The metadata can be changed to get the behavior that you desire, or extended to add more metadata options.
The unique identifier parts are the restrictions you are required to pass to the GetSchema method to retrieve a single unique value.