1. A method of searching for documents using different sources, comprising: receiving a search statement containing information for the documents; determining a search strategy based on the search statement, the search strategy comprising first and second search activities for searching first and second sources, respectively, the first and second search activities being weighted; and searching the first and second sources using the first and second search activities, respectively, wherein an order in which the first and second search activities are performed is dictated by weightings of the first and second search activities.