Approximate Query Answering in Locally Closed Databases
نویسندگان
چکیده
The Closed-World Assumption (CWA) on databases expresses that an atom not in the database is false. A more appropriate assumption for databases that are sound but partially incomplete, is the Local ClosedWorld Assumption (LCWA), which is a local form of the CWA, expressing that the database is complete in a certain area, called the ‘window of expertise’. Databases consisting of a standard database instance augmented with a collection of LCWA’s are called locally closed databases. In this paper, we investigate the complexity of certain and possible query answering in such databases. As it turns out that these problems are intractable, we develop efficient approximate methods to underestimate certain answers and overestimate possible answers. We prove that under certain conditions, our methods produce complete answers.
منابع مشابه
Accuracy and Efficiency of Fixpoint Methods for Approximate Query Answering in Locally Complete Databases
Standard databases convey Reiter’s closed-world assumption that an atom not in the database is false. This assumption is relaxed in locally closed databases that are sound but only partially complete about their domain. One of the consequences of the weakening of the closed-world assumption is that query answering in locally closed databases is undecidable. In this paper, we develop efficient a...
متن کاملTowards a Logical Reconstruction of a Theory for Locally Complete Databases
A relational database stores information about the world. In order to describe how reliable the content of a database is with respect to a certain domain, two cardinal concepts are generally used: correctness and completeness. Correctness refers to whether the database stores only true facts about its intended domain or if it possibly contains false data. Completeness refers to whether the data...
متن کاملAPPROXIMATE IDENTITY IN CLOSED CODIMENSION ONE IDEALS OF SEMIGROUP ALGEBRAS
Let S be a locally compact topological foundation semigroup with identity and Ma(S) be its semigroup algebra. In this paper, we give necessary and sufficient conditions to have abounded approximate identity in closed codimension one ideals of the semigroup algebra $M_a(S)$ of a locally compact topological foundationsemigroup with identity.
متن کاملCooperative Query Answering for Approximate Answers with Nearness Measure in Hierarchical Structure Information Systems
COOPERATIVE QUERY ANSWERING FOR APPROXIMATE ANSWERS WITH NEARNESS MEASURE IN HIERARCHICAL STRUCTURE INFORMATION SYSTEMS Thanit Puthpongsiriporn, Ph.D. University of Pittsburgh Cooperative query answering for approximate answers has been utilized in various problem domains. Many challenges in manufacturing information retrieval, such as: classifying parts into families in group technology implem...
متن کاملProviding Approximate Answers Using a Knowledge Abstraction Database
As database users adopt a query language to obtain information from a database, a more intelligent query answering system is increasingly needed. Relational databases are exact in nature, but effectiveness of decision support would improve significantly if the query answering system returns approximate answers rather than a null information response when there is no matching data available. Thi...
متن کامل