The head of the National Security Agency appeared before Congress Wednesday to defend the bulk collection of U.S. phone data. General Keith Alexander compared the mass sweep of phone records to the running of a library.

General Keith Alexander: “If you look at all the information that is out there, the billions and billions of books of information that are out there, there is no viable way to go through that information if you don’t use metadata. In this case, metadata is a way of knowing where those books are in the library and a way of focusing our collection, the same that our allies do, to look at where are the bad books. From our perspective, from the National Security Agency’s perspective, what we do is get great insights into the bad actors overseas.”

A proposal from Democratic Sen. Patrick Leahy would end the bulk collection of phone records without a court order. But Alexander told lawmakers that even if approved, the measure would not necessarily end warrantless collection depending on judicial interpretation.