As far as I know, there is no simple relationship between a filed against and a build/stream.

To retrieve all repository workspaces associated with a specific stream in IBM's Rational Team Concert (RTC), you can utilize the REST/OSLC APIs, although there isn't a direct API call for this purpose. Start by listing all repository workspaces using the REST API endpoint that retrieves workspaces without stream associations. This gives you a comprehensive list of workspaces to work with. Once you have the list of all repository workspaces, you will need to identify the specific stream ID you are interested in. Since there is no built-in method to query workspaces by stream, you will have to iterate through each workspace and check its properties to determine if it flows into the specified stream. This process can be somewhat cumbersome, especially if there are many workspaces involved. For those comfortable with Java, using the Java API may provide a more efficient approach, allowing for easier access to workspace properties and filtering capabilities. Alternatively, if you prefer a graphical interface, the Eclipse client offers tools like the flow diagram and pending changes view to visually inspect and manage repository workspaces associated with a stream.