数据库应用程序与数据的逻辑组织和数据的物理存储方式无关，表明了数据库的数据具有

A．A-B=B当且仅当A=B=ф
B．若A
SB∧C
D，则(Ａ∪Ｃ)
(Ｂ∪Ｄ)
C．A-(Ｂ∪Ｃ)=(Ａ-Ｂ)∩(Ａ-Ｃ)
D．若A
B∧C
D，则(Ａ∪Ｃ)
(Ｂ∪Ｄ)

A．The definition phase results in the Software Requirements Specificatio
B．Testing is optional in software life cycl
C．CASE tools can only aid in the design phase of a software life cycl
D．A change during a later phase does not require the documentation of all earlier phases to be update