Processing of Null Value in Multiset Relations

doi:10.3969/j.issn.1006-2475.2017.02.016

Abstract

Abstract:

Databases use Null value and duplicate tuples to simulate incomplete information and duplicate entities in real world respectively. Multi-set is allowed to be query’s result in most of existing database, however, these databases still use data models based on traditional set relations to handle Null values, and that would bring hidden danger to database security. In order to formally describe Null value’s behavior in multi-set relations, the paper extends Kleene’s three-valued logic system by adding a new logical connective ψ based on Null’s Unknown interpretation, redefines the multi-set relation data model, and extends the standard relational algebra with Null. What’s more, this paper gives the demonstration analysis of the algebra satisfying properties such as associate law and distributive law, and this makes sense to the query optimization. The extended standard multi-set algebra can be used to handle Null value in database as an abstract query language.

Key words: null, relational algebra, three-valued logic, multi-set relation

CLC Number:

TP311

GUO Yong-ke， MAO Yu-guang， XIANG Ri-feng. Processing of Null Value in Multiset Relations[J]. Computer and Modernization, 2017, 0(2): 78-82.

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