One woman who was not married to a President but who is still considered an official First Lady: Harriet Lane, niece of bachelor James Buchanan. The other non-spousal relatives who served as White House hostesses are not recognized by the First Ladies' Library.
Any distance between two things is called a span. These end points can be physical, like the span of a rope between two trees, or they can be more abstract, such as the span of time between five and six o'clock. Span comes from the Old English spann, the width of the stretched-out hand, measured from thumb to little finger.
Spanner is a scalable, globally-distributed database de-. signed, built, and deployed at Google. At the high-. est level of abstraction, it is a database that shards data. across many sets of Paxos [21] state machines in data-. centers spread all over the world.