's or not

This "double possessive" is quite common so I would use the first in the Alison example.

For the second set, if you are going to the PERSON, use Bob. If you're going to his place (home, office, etc.), the use "Bob's." I can think of a few situations in which you might say "I'm going to Bob," but it doesn't sound particularly natural.

Anonymous

She is a friend of Alison's

She is a friend of Alison

Both are generally considered correct. In Finnish grammar books of English the term "double genitive" is used. The first example is logical if you think of she is a friend of mine. Mine is possessive like Alison's.  However, it would be very inconvenient to insist on a possessive form in cases like she is a friend of Mr. Smith and Mrs. Stevenson's. Or perhaps even she is a friend of Mr. Smith's and Mrs. Stevenson's.

CB