Passing array in GET for a REST call

I think it's a better practice to serialize your REST call parameters, usually by JSON-encoding them:

/appointments?users=[id1,id2]

or even:

/appointments?params={users:[id1,id2]}

Then you un-encode them on the server. This is going to give you more flexibility in the long run.

Just make sure to URLEncode the params as well before you send them!

Collections are a resource so /appointments is fine as the resource.

Collections also typically offer filters via the querystring which is essentially what users=id1,id2... is.

So,

/appointments?users=id1,id2 

is fine as a filtered RESTful resource.