Sensor is a type of Device. Mechanism is a type of Device. 
Supplier is derived from Supply. Gate is a type of Supply. Gate is related to Bridge. you are likely to find Steel in/at/on Bridge. 
Sensor --IsA--> Device <--IsA-- Mechanism 
Supplier --DerivedFrom--> Supply <--IsA-- Gate <--RelatedTo--> Bridge <--AtLocation-- Steel 