区间约束及其代数查询语言

INTERVAL CONSTRAINT AND ITS ALGEBRAIC QUERY LANGUAGE

提出了区间约束和基于区间约束的代数查询语言．区间约束与密序约束相比，增加了简单的加减运算，具有更强的描述能力．同时区间约束元组有简洁、唯一的规范区间表示．文中给出了计算区间约束的规范区间表示的算法．针对区间约束关系，定义了基本代数操作的语法及语义，研究了代数查询语言，并证明代数约束查询语言满足封闭性．最后讨论了区间约束的实现与应用．

Constraint database is regarded as a very promising data model for new database applications such as GIS, Digital Library etc. This paper introduces interval constraint and its algebraic query language. Compared with dense order constraint, interval constraint allows simple addition and subtraction operations, which has more expressive power. And its tuple has a concise canonical form. An algorithm to compute the canonical form for each interval constraint tuple is presented. It is proved that the algorithm is correct and such canonical form is unique. For interval constraint databases, this paper defines the syntax and semantic of basic algebraic operations, studies the algebraic query language, and proves that it has a closure property from the closure property of each basic algebraic operation. Finally issues on implementation and application of interval constraints are discussed. Interval constraint database can be implemented based on relational databases, while current relational database technology being reserved. It can also be used as an index technology for more complicate constraints. That is, it can be used to describe features such as contour of these constraints.