【单选题】关于数据库系统的三级模式结构,下列论述中正确的是( )。
B.
外模式/概念模式映像为数据的物理独立性提供支持
C.
内模式与物理数据库等价,概念模式与逻辑数据库等价
D.
外模式是概念模式的一个逻辑子集,且外模式的某些描述可以与概念模式不同
【单选题】Student loan is supposed to provide financial support for people who would _____ not be able to go to college. [ ]
【单选题】关于数据库系统三级模式结构,下列论述中正确的是( )。
B.
外模式/概念模式映像为数据的物理独立性提供支持
C.
内模式与物理数据库等价,概念模式与逻辑数据库等价
D.
外模式是概念模式的一个逻辑子集,且外模式的某些描述可以与概念模式不同
【单选题】Student loan is supposed to provide financial support for people who would ______ not be able to go to college.
【单选题】Who can go to the head of the line?
A.
People with passports.
C.
People with small bags.
D.
People with small children.
【简答题】A.Most people who go to yard sales are not looking for anything special. B.Some people might buy an object simply because it costs so little. C.Some people enjoy negotiating over prices, even if they ...
【单选题】关于数据库系统三级模式的说法,下列论述中正确的是( )。
B.
外模式/概念模式映像为数据的物理独立性提供支持
C.
内模式与物理数据库等价,概念模式与逻辑数据库等价
D.
外模式是概念模式的一个逻辑子集,且外模式的某些描述可以与概念模式不同
【单选题】The words 'host and hostess' in the last paragraph of Letter B mean ______.
A.
people who go to a party
B.
people who cook dinner
C.
people who hold a party
D.
people who send invitations