Existing explanation systems for deductive databases produce proof trees to be shown to users. Although useful; proof trees give a fragmented view of query evaluations; and users face a; most of the time large; forest of proof trees.
We propose a new data structure; called the DDB tree; which merges the information of a proof tree forest into one concise tree. A DDB tree gives a global picture of a query evaluation in a dramatically reduced structure with no loss of information. DDB trees can be shown to users or can be analyzed further by an explanation system.
Keywords: debugging; explanations; deductive databases; logic programming