let's say now you want to use ViewFacilityInventoryByProduct in a some other component e.g assetmaint in hotdeploy folder.
Define new CommonFacilityDecorator in assetmaint and Then add following line to web.xml file of asssetmaint component.
<description>The location of the CommonFacilityDecorator screen to use for this webapp; referred to as a context variable in screen def XML files.</description>
The location of customer decorator is <param-value>component://assetmaint/widget/facility/CommonScreens.xml</param-value> in the above entry.
View entry in controller.xml file of assetmaint component reads
<view-map name="ViewFacilityInventoryByProduct" type="screen" page="component://product/widget/facility/FacilityScreens.xml#ViewFacilityInventoryByProduct"/>
My screen will use decorator from assetmaint component and not from facility component. So now I have a ViewFacilityInventoryByProduct screen without coping it to assetmaint component.
Hope this helps