ThinkMind // International Journal On Advances in Intelligent Systems, volume 3, numbers 3 and 4, 2010 // View article intsys_v3_n34_2010_8
Bag Relational Algebra with Grouping and Aggregation over C-Tables with Linear Conditions
Keywords: incomplete information; c-tables; relational model; null values; bag semantics
We introduce bag relational algebra with grouping and aggregation over a particular representation of incomplete information called c-tables, which was first introduced by Grahne in 1984. In order for this algebra to be closed and “well defined”, we adopt the closed world assumption as described by Reiter in 1978 and extend the tuple and table conditions to linear ones. We explore the problem of rewriting and simplifying this novel type of c-tables, show how to perform equivalence test for c-tables, and argue why it is difficult to create a canonical form for c-tables. We present certain answer semantics for a full-blown relational algebra with grouping and aggregation and accordingly present algorithms for executing the different relational algebra operators over our representation of incomplete information. The algorithms run in polynomial time relative to the size of the precise information, which makes them a candidate for implementation as part of a DBMS engine that supports storage and retrieval of incomplete information.
Pages: 258 to 272
Copyright: Copyright (c) to authors, 2010. Used with permission.
Publication date: April 6, 2011
Published in: journal