1、关系模型:把世界看作是由实体(Entiy)和联系(Relationship)组成的。所谓实体就是指在实现世界中客观存在并可相互区别的事物。 关系型数据库:是一种以表做为实体,以主键和外键做为表间联系的数据库结构。 主键:用一个唯一的标识符来标识每一行。(特点:不可以重复,不能为空) 外键:用来表达表和表之间的关联关系。
Conceptual design of object-oriented database schemas using the binary-relationship model - Kornatzky, Shoval - 1994 () Citation Context ...ect transition from an OO data model to its implementation as an OO-DBMS. Therefore, there is a tendency to assume that the OO approach can/will ...
The DBMS will maintain at least the precision that you specify. (It may be more.) ◊ BOOLEAN: A logical value that can take only the values true and false. ◊ BIT: Storage for a fixed number of individual bits. You must indicate the number of bits, as in BIT (n) where n is ...
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As far as MS Access goes, I am a novice but I have many years database application development in other PC databases. As a "newbie" I am trying...
Because of the relationship between different bases of logarithm a and b that ∀x > 0 logbx = (logax)/(logab) = (logba)logax, changing base of logarithms has the effect of scaling the logarithms by a multiplicative constant, logba. As such, the choice of base of logarithm is somewhat...