Future data and knowledge base systems will require new and improved functions such as richer data modeling capabilities, more powerful query languages, and new conceptions of query answers. Future query languages will need to include hypothetical, abductive, meta-, and modal reasoning, involving both knowledge and belief. And intentional answers will ultimately lead to cooperative query answering which takes into consideration a user's expectations. This book explores the formalization of new queries and answers, and emphasizes the important role of non-classical logic. It shows how logic...