https://blog.csdn.net/cheidou123/article/details/91442955
1. The log file is used to record ()?
All of the data update
2. the DFD figure is a data flow diagram (Data Flow Diagram), and passing it from data processing point of view, to express graphically the system logic functions, the logic flows to the logic and data transformation process within the system, is the Structured Systems Analysis the method is mainly expressed tools and represents one illustration of a method for software models.
ER is an entity which has contact FIG square and diamond circular
I / O input and output in FIG. FIG.
FIG IPO is an input output processing of FIG.
3. When converting from the E-R model of the relational model, a M: N relationship Information convert mode, the primary key of the relational schema is (). Main master key code combination with the N-terminal end entity entity M
4. The main role of the introduction of two mappings between database model is three ()
Improve data independence
The database, what can defragment operation command table data file
optimize table TabName;