The object model is the central product of object-oriented analysis and design.
All information discovered and documented from other models must be represented in the object model. Object modeling begins in the problem analysis phase.
This might sound like a contradiction. If the object model is so important, shouldn't it be the first model built? No. First you have to find out what you are supposed to be modeling. That is why the problem statement, data dictionary, and use case model are so valuable. Without an accurate statement of purpose, there is no objective target for the modeling process.