Cédrick,
The basic difference between SAX and DOM is that SAX is like a stream that as it is read provides information to you to build the objects you need, while DOM is more like a tree or object model that can be traversed like regular objects. They both have their advantages. The big advantage for SAX is in parsing large files. Since it acts like a stream you can build objects on the fly and not have to parse the entire file before getting a single object. DOM is much easier to use since it builds a tree for you that can be traversed.
For DOM to create an object you need to build your own object form the data that each node of the tree provides to you. The tree is a collection of collections with each item an XMLElement that can respond with queries like elementAt: #... you can iterate over the collection creating objects as you go.
For Sax you wait for a tag that indicates starting a new object then you create the object and for each element that comes after you add data to your object until you hit the end object tag.
If you are going to XML then you should learn both (which it seems you are doing). Good luck with it and feel free to let us know how you are doing with it. If you need more help let us know.
Ron Teitelbaum President / Principal Software Engineer US Medical Record Specialists Ron@USMedRec.com