变量查询代数及最短路径分析

Variable Query Algebra and Shortest Path Analysis

本文简单分析了满足ＧＩＳ空间查询代数的一般要求，然后形式化地定义了一种适合于ＧＩＳ空间查询的变量查询代数。在此代数中，将谓词划分为３类：原子谓词、特征谓词和空间谓词，以适应目标的空间运算描述；为此代数定义了七类形式的运算，其中的投影运算π、聚集选择σΣ、极限选择σΜ和分裂选择σＳ拓广了一般查询代数的查询空间，此查询代数的独特之处在于能完成的网络分析功能；最后给出最短路径查询的实验。

General requirements of spatial query in GIS are briefly outlined in this paper. A Variable Query Algebra is formally defined for spatial query of GIS. In this algebra, predicates are divided into three kinds catering for description of spatial operations. This algebra includes 7 operators, among which Projection π 、Aggregate Selection σ Σ 、Limitation Selection σ M and Splitting Selection σ S extend the query space of common query algebra. It is the unique feature that this query algebra can complete network analyses. Finally, a query example for shortest path analysis is used to show the capacity of this algebra.