I'm, a bit confused about fortifications.

This is how I understand it:

If an army encounter a fortified province, it can not pass though that province unless it neutralize the fortification. To do this the army must set fortification level number of units to lay a siege to the fortification. As soon as the siege is started the rest of the army can freely move though the province (unless there is a defending army there).

If the attacking army choses to storm the fortification, the defender get a free attack on all units storming the fortification, even if there is no defending army units. After this there is a opsed warcraft check between the attaking and the defending general with a sum of their melee score as bonus, and +4 for attacking if they have artillery, and +2xfortification level for the defending. If the attacker win there will be a battle on open ground.

If the attacker do not chose to storm the fortification it is reduced by 1 for each season of siege.

Before you can make the province yours you have to either storm the fortification or reduce it to zero by means of siege.

Is this correct?