Is Kingdom Hearts 358 2 just the first and second put thogether

Well, sort of like that, except it only shows Sora few times. Originally, this is supposed to be Roxas's story of being in organization 13. It is what we call a "sidetrack game" to fill in the missing spots of kingdom hearts 2. People are usually saying who is this Roxas guy and why do I play as him in the first part of kingdom hearts 2?" Well, that's where the creator put a little mystery, so a sidetrack game would seem useful. So Kingdom Hearts 358/2 Days is only after Kingdom Hearts, and before Kingdom Hearts 2, Where you play as Sora's nobody, Roxas (Or even the members from organization 13).