Soft exam -- software designer -- afternoon question data flow diagram DFD

     Basic ingredients ：

put questions to

Usually the first three questions are all about ：

1. Entity E1-E4
2. Storage D1-D4
3. Missing data stream / Store data streams

The last question depends on the situation

They usually give Top level data flow diagram Follow 0 Layer data flow graph

1、 Seeking entity ：

Sometimes a paragraph corresponds to a process , This can be used as a breakthrough

A figure 1 Follow chart 2, Directly according to the figure 2 Find entity
Like looking for p4 Drug Administration , Just go back to the paragraph 4, Combine the input and output data flow to find the entity
An entity can be （ people , matter , System ）
If the title is about development A System , Then the paragraph says use B System to complete , that B The system can act as an entity

The paragraph says , The doctor submits the medicine , therefore E2 It's the doctor , Just look for... One paragraph at a time , After finding it, you'd better verify it , such as E2 Will receive “ The medicine has been prescribed ” feedback , You can verify whether this is described below

If the paragraph does not match the workings , It is possible to have two paragraphs describing a process , You can find the processing with less data flow first , Find the corresponding entity , You just have to do more questions , It's easy to find

2、 data storage

Processing points to data storage , Judge the paragraph , Find the data store
Usually use （… surface ,… file ,… archives ,… Record ,… library ） Express
But it's not that obvious now , Will say The data is recorded in … 、 Data storage 、 according to … data , obtain … data , take … data , utilize … data Saying things like, .
As we write our answers , If it is not clear, just look at the data flow name XX Information sheet

In fact, I haven't said much about data storage here , But you can see what data he inquires based on , The drug inventory data is from D5 To P5 Of ,D5 It can be directly expressed as a drug inventory information table
One more thing is ： According to the reservation data 、 Visiting time … You can see in the picture , If not, it means that there is a missing data flow

3、 Missing data stream 、 Error data flow

Data flow missing （ First, balance according to the parent-child graph 、 The following process should have both input data flow and output data flow , If found, mark in the figure first , Then check one by one according to all the paragraphs , This will not leak ）

①（ Parent child graph balance ） Input of a machining in the parent diagram / The output data flow must be input to its subgraph / The number of output data streams is the same as the name , The same direction

This is the same , If you don't find it, it means that there is a missing data flow , Look at the picture 1 Each data flow of is shown in Figure 2 Whether it exists and is correct
eg（ chart 1 Data flow A/ Data flow B chart 2 Only A, That explains. defect B）
（ chart 1 The data flow is from E1 Point to D1 chart 2 yes D1 Point to E1, That's it Data flow error ）

② Data processing has input and output （ Output stream ）
Only the input （ Black holes ）
Only output （ Miracle ）

This is only input but no output

③ Find missing data flow in paragraph , That's the most important thing , Look carefully , If you do more questions, you will find them naturally , The paragraph says , Based on what , You should pay attention to whether the data is stored in other storage , Data flows that are not yet in the graph


D1 It is the sales order form , He has the data of sales orders , This indicates that there is a lack of data flow

Data stream name	The starting point	End
Sales order	D1	5

The title may also say ,XX Store information ,XX The information includes , full name , Gender …
machining P4： Review by name , Then you have to see if it exists XX The information table points to P4, And a data stream with the name , Many missing data streams start from data storage , Because the data stored in the data store is used , So pay more attention to the expression of the article

summary

Is to do more questions , Then sum up more , Read the description carefully , You can find the missing data stream by looking at it several times

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