Does Facebook use-case have one or more actors?

Question

As a class project I must make 5 use-case diagrams after analyzing Facebook web page. My doubts arise when whether to include FACEBOOK as an actor or simply use the user as a single actor system.

Overall, I've made my diagrams like this.

1. Use-case create an account:

http://i59.tinypic.com/2s63oe1.jpg

Here the actor has the role of being a "visitor" and it creates an account through a use-use named "create account". When checking for registered users should Facebook, as an actor, take part in that use-case?

2. Use-case login:

https://i.stack.imgur.com/XxcqD.png

Here an already registered user login into the page and gets both his email and password check by Facebook. I tried using Facebook as an actor, but I'm not entirely sure if that is correct.

3. Change profile image:

i60.tinypic.com/95onr4.png

Again, tried to use Facebook as an actor.

4. Manage friends:

i61.tinypic.com/2n67xp1.png

I gave options using the "extends" and made the use-case "manage friends" to include "check friends" through Facebook as an actor. Here, as in my previous cases, I'm not sure whether Facebook should be considered as the system or it can interact as an actor.

5. Publish to wall:

i61.tinypic.com/28mlo5h.png

As my last diagram I tried to represent the action of publishing to wall. Should adding a message be mandatory? and should it interact with Facebook as an actor?

Also, if someone could point out if my use-cases are done correctly.

Answer 1

An Actor by definition is external to the system under consideration.

Therefore if you are writing use cases for the system Facebook then Facebook itself cannot be an Actor.