A <e1>chain</e1> <e2>saw</e2> is one of those tools that can be described thusly: When you need one, nothing else will really do.
A chain saw is
A chain saw is one of those tools that can be described thusly: When you need one, nothing else will really do.
<triplet> chain <subject> saw <object> Component-Whole(e1,e2)