One may define a "time-constrained database" as a database that has strict timing constraints in (a) responding to queries, (b) processing transactions, and in (c) database maintenance. A "time-constrained query" has the form of "get the information x in no more than t time units". This project deals with the problem of processing arbitrary time-constrained queries in centralized and single-user time-constrained databases. Various ways of revising a query into one which has the most "informative" response and can be evaluated within the given time constraint with a controlled risk of overspending are investigated. Techniques for fragment selection and risk analysis are introduced. Semantic query processing techniques to control the query processing times are investigated. The expected outcome of this research is (i) a methodology to process queries with time constraints, (ii) a prototype time- constrained database management system and a performance evaluation using the prototype, and (iii) heuristics about the use of various options under different data characteristics. Potential applications of the research results are in those areas where time-critical database processing is important, e.g., scientific applications and manufacturing environments.
