Object-Relation Model of ORACLE Spatial Database: with Discussion of RDB and OODB Application in GIS
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摘要: 传统的关系数据库在GIS的应用中主要存在以下问题: 除数据类型简单, 不能很好地表达非结构化数据外, 也难以表示GIS中具有复杂结构的数据; 关系模型简单, 不能表达数据之间的层次, 继承、聚合、泛化或特化等在GIS广泛使用的关系; 与数据操纵语言如SQL和通用程序设计语言, 特别是目前流行的面向对象设计语言之间失配.采用面向对象技术可以较好地解决上述问题.ORACLE的空间数据库在传统的关系数据库上进行了面向对象的扩展, 即所谓对象-关系模式, 其核心在于增加了名为SDO-GEOMETRY的对象数据类型, 用于存储几何实体.ORACLE的空间数据库的应用示例表明: 以面向对象的形式表示空间数据比之于关系数据库中存放大量无意义的坐标有着很大的优势, 同时, 它在复合对象的表达方面, 在对于空间关系的处理方面都非常有效Abstract: There are some problems of RDB in GIS application. Sometimes the data type is too simple to describe non-structured or complex-structured data in GIS and the simple model can't express the relation of hierarchy, inheritance, aggregation, generalization or specialization, or there is impedance mismatch between SQL and programming language, especially the current popular object-oriented language. While object-oriented (OO) technology may be useful to solve these problems. ORACLE spatial database extends the traditional relation database with the technology, the so-called object-relation model, which features adding to RDB an object data type named SDO-GEOMETRY to store geometry. An application example of ORACLE spatial database demonstrated the advantages of OODB in describing spatial data and the efficiency in expressing compound object and processing spatial data compared to RDB which only stores meaningless data. Certainly, there are still some issues that need further research in OODB: which direction OODB will develop: pure OODB or object-relation DB, the data model match between RDB and OODB, the mathematic basis and formalization for OODB and how to take advantages of existing mature technologies of RDB such as transaction control, integrity check, data reproduction in the development of OODB.
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