Relational Data Model
■The basic data structure is "table",or relation.The things and the relationships between them in real world are all expressed as tables,so it can be researched in strict mathmatics methods.It raises the database technology to a theory height.It features:
关于基本思想，层次和网状数据模型中，实体用记录来表达，实体之间的联系用PCR关系或系来表达。而关系数据模型则是实体以及实体之间的联系都用表来表示。这样的话，数据库中存储的是表，查询等操作的结果也是表，这样就形成了一个封闭空间，我们就可以在这个封闭空间里面定义一个代数系统，即我们后面说的关系代数。
►Based on set theory,high abstract level
►Shield all lower details,simple and clear ,easy to understand
►Can establish new algebra system--relational algebra
►Non procedure query language--SQL
►Soft link--the essential difference with former data models