Well one is necessary for the other. I don’t know if I would talk about them in terms of pros and cons. One document is necessary for the other. Let’s stick with the door knob example. You need a basic understanding of what is wanted. That’s what the DID document is for. An understanding of what is needed is formulated in this document. If you get down to the details, like in the DSD, you may constrain yourself too much too quickly. Knowing the generic needs allow for easy change later. You can work off the DID. If you start with the DSD, and then you need to make a change, you don’t know what aspect of the DSD was required. Then you have to go back and waste time checking what would be in the DID.