Date: 31 May 2006

An overview of cooperative answering in databases

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The field of cooperative answering goes back to work started by Joshi and Webber [12] in natural language processing in the early 1980s at the University of Pennsylvania. The work was applied to databases and information systems at the University of Pennsylvania by Kaplan [14, 15] and Mays [17]. Other early work at the University of Pennsylvania and at other universities is discussed in [25, 13, 26, 16, 18, 24]. Databases and knowledge base systems are often difficult to use because they do not attempt to cooperate with their users. A database or a knowledge base query system provides literal answers to queries posed to them. Such answers to queries may not always be the best answers. Instead, an answer with extra or alternative information may be more useful and less misleading to a user.

This lecture surveys foundational work that has been done toward developing database and knowledge base systems with the ability to exhibit cooperative behavior. In the 1970s, Grice [11] proposed maxims of cooperative conversation. These maxims provide the starting point for the field of cooperative answering.

To develop a general system for data and knowledge bases, it is important to specify both the sources of information needed to provide cooperative behaviors, and what constitutes cooperative behavior. Several sources of knowledge apply: the basic knowledge in a system is given by explicit data, referred to as data in a relational database, or facts (extensional data) in a deductive database; by general rules that permit new relations (or new predicates) to be developed from existing data, referred to as views in relational databases and as intensional data in deductive databases; and by integrity constraints that must be consistent with the extensional and intensional data. Integrity constraints may be obtained either through the user or the database administrator, or by a data mining capability. Whereas integrity constraints must be consistent with every instance of the database schema, another source of knowledge is state constraints, which may apply to the current state, and need not apply to a subsequent state upon update. Two additional sources of knowledge arise from information about the users. One describes the class of the user, for example, an engineer or a child, each of whom expect different kinds of answers to queries, and user constraints that must be satisfied. User constraints need not be consistent with the database, but reflect the interests, preferences and desires of the user.

Alternative cooperative behaviors are explained and illustrated by examples. The cooperative behaviors discussed are:

  1. Misconceptions. A misconception is a query for which it is not possible, in any state of the database to have an answer.

  2. State Misconceptions. A state misconception is a query for which it is not possible to have an answer, given the current state of the database.

  3. False Presuppositions. A query has a false presupposition when it fails to have an answer, but is neither a misconception nor a state misconception.

  4. Intensional Answer. An intensional answer is a generalization of a query which provides a rule that satisfies the query, but does not necessarily provide data that satisfies the query.

  5. Relaxed Answer. A relaxed answer to a query is an answer that may or may not satisfy the original query, but provides an alternative answer that may meet the needs of the user.

  6. Scalar Implicature. A scalar implicature is a range that may meet the query.

  7. User Goals, Inferences and Preferences. User goals, interests and preferences should be adhered to when answering a query.

A brief description is provided of three systems that have been implemented, which exhibit cooperative behavior for relational and deductive databases. The systems and their features are:

  1. Cooperative AnsweRing Meta Interpreter (CARMIN), developed at the University of Maryland by Minker and his students [9, 8, 10].

  2. Misconceptions.

  3. State Misconceptions

  4. False Presuppositions

  5. Intensional Answers

  6. Relaxed Answers

  7. User Goals, Interests and Limited Preferences

  8. CoBase, developed at UCLA by Chu and his students [3,2,1,4,5]. A language, CoSQL has been implemented and interfaced with an existing database (Oracle) and SQL.

  9. Intensional Answers

  10. Relaxed Answers

  11. User Goals, Inferences and Preferences

  12. FLEX, developed at George Mason University by Motro [23, 19–22].

  13. Well Formedness Test of Queries and Automatic Modification

  14. Relaxed Queries

  15. False Presuppositions

For a discussion of the state-of-the-art of cooperative answering systems, see

A functional description is provided of a cooperative database system. It is currently possible to develop a cooperative capability that interfaces with any of the existing database systems. Since proposed and future versions of relational databases will include capabilities to handle recursion and semantic query optimization, the ability to include cooperative capabilities will, in the not too distant future, be incorporated into such systems.

Invited Paper, Flexible Question Answering Systems, May 13–15, 1998, Roskilde, Denmark