1. A device implementable in a web site design program, said device comprising: a component based version comparer to compare at least two versions of a website, said at least two versions having components in a set of hierarchies, wherein said components are at least one of a visual component, a container and a non-visual site element, and to generate a difference tree representing the differences in said components between said at least two versions of the same website, wherein said version comparer preprocesses said components in each single version of said at least two versions of said website to determine at least one of internal geometric, semantic, content and attribute relationships before comparing said components and said relationships between said at least two versions of said website using at least one of semantic, geometrical, content and attribute analysis; and wherein said hierarchies and said difference tree are trees and wherein said trees comprise nodes representing said components, said components having attributes; and wherein said component based version comparer comprises: a structural version comparer to compare nodes of said at least two versions of said website through comparison of their geometrical, content and semantic relationships; an order based version comparer to compare said nodes of said at least two versions of said website based on the order of said nodes and to pre-match said nodes according to an internal said website design system identifier; a semantic matching comparer to perform semantic classification on said nodes of said at least two versions of said website and match them according to their semantic classes and geometrical parameters; a comparison selector and coordinator to provide selection and coordination between said structural version comparer, said order based version comparer and said semantic matching comparer based on at least one of the structure and attributes of said components; a difference tree generator to generate said difference tree based on a combination of the results of said structural version comparer, said order based version comparer and said semantic matching comparer; a version merger to create an integrated version of said two versions of said website based on said difference tree; and a processor and a memory unit, said processor to activate said component based version comparer and said version merger.