Scene Graph, Concept, Design and Implementation?

[MasterGod]

Scene Graph, Concept, Design and Implementation:
====================================
1. What is a Scene Graph?
2. Relation between Scene Graph and Irrlicht?
3. Example implementation of a Scene Graph?

- I have a clue about those questions but to be sure I'm not completely wrong I still ask.

- I've also found a lot of information using Google but I want to hear what you guys, who are real living people whom I can ask what you mean, have to say.

I'm interesting in learning that because I think this is what I need for my following requirement (yes rogerborg, I do have such list )
Every scene, a bedroom, a football yard, a slaughter house etc, should be a separate "thing" I mean every scene should have its own sub objects.
To have such scenes I need a data structure that will be able to know which objects belong to which scenes. This way I can know exactly what needs to be loaded/unloaded in each scene dynamically etc..
I thought of making as much irrSceneManagers as scenes but that sounded just wrong although my main idea was using irrlicht's scene graph and so I realized I need my own scene graph for my engine which is independent of irrlicht.
Ico introduced me to a first design thought:

Warning - ASCIIart inc!

Code: Select all

+-RootSceneNode (in SceneManager)
  +-MainMenu (visible in addition when menu is opened)
    +-Logo
    +-MenuEntry
    +-MenuEntry
    +-MenuEntry
  +-House (only visible when inside your house)
    +-Chair
    +-TV
    +-Toilet
  +-Yard (only visible when inside the yard)
    +-Tree
    +-Tree
    +-Football
  +-Street (only visible when on the street)
    +-Car
    +-Car
    +-TrafficSign
    +-People
    +-People
  +-Shopping Mall (only visible when in the mall)
    +-Cart
    +-Cart
    +-Products
    +-Products
    +-Customer
...

Think you'll get it. However it all depends on how complex your gameworld is. If you have many objects, physics engine, big textures, etc. It might be better to include a simple loading screens and drop everything when changing area/level/chapter (except the SceneManager etc. of course).

Now on this part of my engine I'm willing to invest a lot of time considering and designing because it's a very important part I must think and design carefully.
I want my scene graph to be designed efficiently and still keep a simple aspect to it.
What I'm basically asking is how to design it? After I'll have a pretty solid design the implementation shouldn't be that hard and I'm willing to learn new things to make it good.
Also, I need something realistic because it needs to be implemented in no more then 1 month and that's even too far away, don't forget my project has a deadline.

I guess because irrlicht has a scene graph it would be the best implementation example for me so pointing me to where it is would be very helpful indeed.

P.S
For anyone who didn't understand, I'm not asking you to do any homework for me, just to guide me through the process of designing a scene graph which I'll describe here as the progress advances for feedback.

Thanks !

EDIT:
I've been adventuring inside CSceneManager and ISceneNode and I learned a LOT of new things, design-wise. After going through forests and rivers, ups and downs I reached a point a question was undeniable, what IS the Root scene node. That was the peak of my adventure when I discovered the scene manager itSelf was a scene node, the amazing root scene node. Well, I was listening to opera while going through the sources of irrlicht so it might have influenced me a bit
I like classic music and there's nothing I can do about it