Art can be unintentional it all depends on how it is depicted by the person viewing it. For example I once made a coin display case with the intention of it holding coins. I did not intend on it being art. However as it developed some of my friends saw it and told me I was an artist with the way I had constructed it. It was completely unintentional but now I have a display case that many consider a work of art.
As for art being representational that is defiantly in the mind and thoughts of the person who sees it. For example I may see a painting of George Washington and to me it would represent a hero of the ages. It would depict a man that fought hard and left a legacy that can be looked up to by all Americans. However if you were to go back over 200 years and show this same painting to a solider from great Britain this painting would represent a trader and someone they hate. They would look at the painting similar to the way we look at videos of Osama bin laden. This would be one piece of art representing two totally different meanings. It is almost impossible for one person to try to define what a piece of art should represent. Even today as archeologists try to interpret what some of the art they dig up means they could be way off. I mean what if they are getting it all wrong who is there to say what that artist meant when they created that work. You really can’t so that leaves an open door for people to interpret art however they want.