'Big data" is one name for the insight that collecting all the information in a massive database will uncover facts that collecting only some of the information cannot. This is not news to Gen. Keith Alexander, director of the National Security Agency. Gen. Alexander is a zealous advocate of getting it all whenever practically and legally possible. He sees increased agility in uncovering terrorist connections by acquiring vast databases of telephone records, including those of American citizens.

Now the intelligence community's...