AT&T;
2600 Camino Ramon
San Ramon, CA 94583

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Data Management Association
San Francisco Bay Area Chapter

CHRIS DATE


January 10, 2007
8:30am - Noon

AT&T;
2600 Camino Ramon
San Ramon, CA 94583

Abstract: The Closed World Assumption
The Closed World Assumption (CWA) is an important concept in the database world, despite the fact that it isnít usually spelled out explicitly. Basically what it says is this: Everything stated by the database, either explicitly or implicitly, is true; everything else is false. This presentation explains the CWA in detail and shows why itís preferred over its rival, the Open World Assumption (OWA). In particular, it examines the claims that are sometimes heard to the effect that the database community operates under the CWA while the semantic web community operates under the OWA. It also explains how "missing information" can be handled under the CWA without any need for nulls or three-valued logic.

Topic Outline

  • Background review
  • Relvar predicates and constraints
  • The CWA and OWA defined
  • Relvar predicates revisited
  • Unknown and uncertain information
  • Negation and disjunction

Chris Date - Biographical Information
C. J. Date is an independent author, lecturer, researcher, and consultant, specializing in relational database technology (a field he helped pioneer). Before leaving IBM in 1983, he was involved in technical planning and design for the IBM products SQL/DS and DB2. His book An Introduction to Database Systems (2004), currently in its 8th edition, is the standard text on the subject; it has sold well over 700,000 copies not counting translations and is used by several hundred colleges and universities worldwide.

He is also the author of many other books on database management, including in particular Database, Types, and the Relational Model: The Third Manifesto (Addison-Wesley, 3rd edition, with Hugh Darwen), Temporal Data and the Relational Model (2003, with Hugh Darwen and Nikos A. Lorentzos), The Relational Database Dictionary (OíReilly, 2006), and Date on Database: Writings 2000-2006 (Apress, 2006). He enjoys a reputation second to none for his ability to explain the complexities of database technology in a clear and simple fashion, both on paper and in live presentations.