Journal of Geo-information Science >
Concept of Spatial Constrained Pairs and Its Implementation
Received date: 2015-03-10
Request revised date: 2015-04-20
Online published: 2015-09-07
Copyright
Equal classes play an important role in the generation and optimization of query plans. In order to reduce the search space of query plan, Ingres often takes two attributes that connected by a non-equal spatial topology relation operator as an equal class, and puts a spatial join operator between them to the bottom of the query plan tree. After filtering the spatial topology relation operator, the database system will have fewer data to proceed in the following operators, and produce higher efficiency. However, if take them as equal classes, just as in Ingres, it often results in building some errors in the spatial query plans especially for some queries with multiple spatial joins. Therefore, the non-equal spatial relation operators are not an equal relation. This paper analyzes the reason why non-spatial topology relation is not an equal relation and puts forward to use the spatial constrained pair instead of equal classes. The paper also gives a definition of a spatial constrained pair, which is an attributes pair connected by a non-equal spatial relation operator, or the spatial column of a table and the KEY column of its spatial index table. Spatial constrained pair is a sub-concept of equal class. It could adopt some heuristic strategies of equal class on building query plan except for transitivity. The paper explores a database implementation about the spatial constrained pairs in Ingres. Taking consideration of a query with multiple spatial joins, this paper conducts two tests. One takes the attributes pairs connected by a non-equal spatial relation operator as equal classes; the other one takes them as spatial constrained pairs. If follow the heuristic strategies of equal classes, it will produce some errors in the procedure of plan generation. However, if follow the heuristic strategies of spatial constrained pairs, it could help the system find the best query plan.
CHENG Changxiu , YANG Shanli , SONG Xiaomei , WANG Lijun . Concept of Spatial Constrained Pairs and Its Implementation[J]. Journal of Geo-information Science, 2015 , 17(9) : 1009 -1013 . DOI: 10.3724/SP.J.1047.2015.01009
Fig. 1 Demo of non-transitivity on intersects图1 Intersects不具传递性示意图 |
Fig. 2 Mask up spatial constrained pairs from list of equal classes图2 屏蔽等价类序列表中的空间约束对 |
Fig. 3 Test data图3 测试数据 |
Fig. 4 A building error before masking up spatial constrained pairs图4 空间约束对被屏蔽前的编译错误 |
Fig. 5 An optimal query plan in Ingres after masking up spatial constrained pairs图5 Ingres查询计划 |
The authors have declared that no competing interests exist.
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