The first soft test over, record a wave of test preparation experience, next time (not) come again!! (With PV operation and data flow diagram analysis)

I signed up for the examination of a total of two subjects, morning and afternoon each test a subject: — basic knowledge in the morning, are multiple choice questions, empty one point, a total of 75 points; Afternoon word problems, all big questions, 15 points for each question, 4 questions must be done, there are two two to choose one, a total of 75 points;

Since I began to prepare for the exam, the exam about 20 days, look at knowledge again, to solve the problem. The time is not enough, and I also want to look at their base (one thousand didn’t finish my review/meet won’t do, look at your casting ability haha), decided not to review, blind “sprint”, finish a chapter, for the answer, see the parsing, don’t understand to double material, understand later went on to the next chapter

— This method is not recommended here. Slow and steady is better. — The official launch of question bank small procedures, easy to brush questions; There are supporting teaching video, but I did not listen, on the one hand I feel time is pressed, the fastest to read, on the other hand because of the fee ε(┬┬﹏┬┬)3

Operating system this chapter has a PV operation question, “with PV operation control process concurrent execution”, classical high frequency examination point. Here’s an example:

Figure 3-2 shows the precursors of processes P1, P2, P3, and P4.





If PV is used to control the concurrent execution of process P1 to P4, four semaphores S1, S2, S3 and S4 need to be set, and the initial value of the semaphores S1-S4 is equal to zero. In Figure 3-3, a, B, C, and D should be filled with _ respectively_ the _ (16)_

(16) Dr. (S1) V (S2), V (S4), P (S2) and P (S3), P (S4) B.V (S1) V (S2), V (S4), P (S3) and P (S2), P (S4) c. (S1) V (S4), V (S2), P (S2) and P (S3), P (S4) D.V(S1) V(S4), V(S2), P(S3) and P(S2), P(S4)

The options given are the operations to be filled in at a, B, C and D respectively, where a and D both have two operations

Analysis topic: According to the precursor diagram, there are 4 paths, respectively:

• P1->P2
• P2->P3
• P3->P4
• P1->P4 where P1 has no precursor process, so P1 is executed first; However, the execution of process P4 can only be carried out after process P1 and P3 are completed

The book Sprint gives us a good rule to solve the problem:

• One path corresponds to one semaphore;
• In the source process of a path, V should be performed on the semaphore corresponding to the path.
• In the terminal process of a path, P should be performed on the semaphore corresponding to that path

Let’s take a part of the picture from the title to illustrate:

In the precursor diagram,

• P1-p4 are the processes to be executed, represented by circles;
• S1-s4 are semaphores marked along the path

In the flow chart,

• P1-p4 is the process to be executed, and the execution process is marked on the arrow path;
• PV operations on semaphore S1-S4 are represented by rectangles

Taken together, the top rectangle refers to P operations on the semaphore S, and the bottom rectangle refers to V operations on the semaphore S. If the semaphore is used as the key to the door, each process is locked in a separate room, opened and executed sequentially; There are keys to open the door, some doors need to have two keys; After opening the door, you need to return the key, and then execute the process. When the current process completes, it needs to get the key for the next door. Where obtaining the key is the V operation to the semaphore and returning the key is the P operation to the semaphore

Substitute into the problem:

• First look at the precursor diagram, P1 has no precursor process and is executed first, and does not involve semaphore operation. After P1 is executed, the key of P2 and P4 process is obtained, that is, two V operations are required.
• After P1 is executed, P2 is executed, and before P2 is executed, P is performed on the S1 semaphore, so the semaphore on the path P1->P2 is S1
  
  
• In the flowchart, V operation is performed on semaphore S3 after P3 execution, so the semaphore corresponding to path P3->P4 is S3
  
  
• Since the execution of P4 process needs to acquire two keys, one is the semaphore on the path P1->P4 and the other is S3, so before the execution of P4, two P operations are required, one of which is P(S3). The semaphore on paths P1->P4 is S4, and the semaphore on paths P2->P3 is S2

• After P1 is executed, it is necessary to obtain the keys of the back drive process P1 and P4, namely, V(S1)V(S4), and a is solved empty
• After the completion of P2 execution, the next key needs to be obtained, that is, V(S2), and B is empty solved
• Key S2 is returned before P3 execution, that is, P(S2), and C is empty solved
• P(S1) P(S4) P(S4

First look at the data flow diagram, at the beginning of the three questions, a large paragraph and complex connection almost made me dizzy, this is something I can understand?? After a few days of calm, I picked up the topic and began to look at it slowly. Here is a classic example and personal analysis. If there is anything improper, please give me your advice

Topic: Sprint, Chapter 12, question 3

A marketing enterprise plans to develop a sales management system, its main kinetic energy is described as follows: (1) accept customer orders, check whether the inventory of goods meet the order requirements. If it meets the requirements, supply process, that is, revise the inventory record file, issue the inventory list to the warehouse and keep the customer order to the order record file; Otherwise, the stock is out of stock and the stock record is stored in the stock out record file. (2) The stock is out of stock statistics according to the stock out record file and the stock out notice is sent to the procurement department. (3) Stock processing is carried out according to the purchase notice provided by the procurement department, that is, modify the stock record file. (4) Sales statistics are made according to the reserved customer orders, and statistical reports are printed to the manager. Now structured methods are used to analyze and design the sales management system, and the top-level data flow diagram as shown in Figure 12-6 and the zero-layer data flow diagram as shown in Figure 12-7 are obtained

The questions are as follows:

1. Use the words in the description to name the external entity E1-E4 in Figure 12-6 2. Use the words in the description to name the data store D1-D3 in Figure 12-7 3. There are four data flows missing in the layer data flow in Figure 12-7:0. According to the description and the information provided in figure 12-6, point out the starting point and end point of these four data flows respectively

At first glance, it was a long piece of text, not on the same page. It was difficult to turn over and over, unable to understand and remember. So many marks and symbols were just arrows and boxes for me. It wasn’t until I did about five or ten problems that I realized that there was actually a pattern

Some of the markers used in the general test are:

1) rectangular box, on behalf of an external entity, often is the beginning and end of the data source, is the person or the organization exists in the software system, is a noun (2) the rounded rectangle commonly, on behalf of processing, is the flow of the input data to the output data stream, the transformation between the general is subject to requirements of system (3) arrows, on behalf of data streams, said the flow of data, Data flows can be divided into the following categories:

• Flow from one process to another
• From processing to data storage (write)
• From data storage to processing (read)
• Flow from external entity to processing (input)
• From processing to external entities (output)

(4) Unenclosed rectangles, representing data storage,

The illustration is as follows:

Data flow graph examination questions is to take an examination of commonly identify external entities (1) (2), identify data storage, and data stream (3) additions/corrections, and may take an examination of some concepts, such as the “balance of hierarchical data flow graph of father and son figure”, these can go to the book, or look over the years love what concepts, from the high frequency test of a little extension, Understand and remember

When I get the title, I explain that the text is the most important, so I must read it well. I am used to reading while following the text and drawing the draft, so that I can understand it by myself. The main purpose is to help understand and briefly sort out key information such as relationships, data storage and external entities. Of course, you can also draw your own data flow diagram to show that you have a good grasp of the knowledge. But upgrade to play strange, there is always a low-level state, I draw the basic are unconstrained, a problem repeatedly look at a few times, before gradually drawing closer to the data flow diagram given by the topic

Let’s look at the problem. Let me take a screenshot of the previous problem

processing:

In order to design a sales system, we need to design a sales system. Therefore, the sales system is the core of the whole picture. All the data flow and data storage are around it



An external entity

As mentioned earlier, external entities are individuals or organizations unrelated to the software that are the source or destination of data. External entity is generally a noun, and the content of this noun is human, and the processing (sales system) interaction, together to complete a process. In the topic above, it can be found that they are: customer, Warehouse, Purchasing Department, manager

Question 1 can be filled out based on the context and the method of elimination. For example, print the statistics report to the manager. E4 is the manager

答案 : 1.

Note: in the real answer, E2 is the purchasing department, E3 is the warehouse, I do not agree, because the notice of shortage is for the purchasing department, not for the warehouse

Next, the data store

Data storage, in the examination of the contact, generally refers to a certain file, a certain table, etc., the question will describe the file read and write operations, generally also a noun. In addition, data stores generally do not appear in the top-level data flow diagram. The data stored in this document is inventory record file, out of stock record file, order record file

Then determine where the data flow diagram should be filled according to the context

D3 is the order record file. D3 is the order record file. D3 is the order record file.

(2) In the question, the inventory record file and the out-of-stock record file appear close to each other. When there is no clear relationship between the two and the processing process, it is easy to confuse them

From the general direction, after receiving an order, there are two situations: one is available, modify the inventory record file; The other is out of stock, fill in the out of stock record file, “out of stock” should be the right half of the figure, “out of stock” should be the left half of the figure; Because “out of stock” and “out of stock notice” is associated, “in stock” is associated with “purchase notice”, “report”, “inventory”. Read the question carefully and patiently, you can find the answer

So far, question 2 has been solved:

Read the first two questions, in fact, have a certain understanding of data flow, data flow has a starting point, end point, data flow name. Here is a screenshot of the concept mentioned above for easy viewing:

Understand the direction of the data flow rules, knowWhere can I start and where can I goThis is important in the title of “Supplementary data Flow”. Here we look at one by one:

First, from A processing flow to another processing when the main processing is decomposed into many sub-processing, there will be this situation, sub-processing B depends on the completion of sub-processing A, or, sub-processing A completed, then the execution of sub-processing B; I’m going to draw it from one rounded rectangle to another rounded rectangle and I don’t see that in the picture that they gave us and I’m going to add a little bit of processing information here. A problem might refer to all subprocesses by the name of the system it wants to solve; As in this case, the sub-processing has been named “sales management system”. We need to think about, what are these subprocesses, to help us understand the question more clearly, to see the data flow diagram

General sub-processing can find verbs first. Based on the information given in the question, we can roughly figure out what these sub-processes mean (red text).

Note: Since in Figure 12-7 given by the title, D1 points to the sub-processing and then sends “out-of-stock notice”, I choose “Out-of-stock statistics” instead of “Out-of-stock Processing” as the name of the sub-processing here.

For example, in this case, “modify inventory record file” is a write process. The arrow points from “sales system” to “inventory Record file”.

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Third, from the data storage to processing (read) generally refers to, a processing (processing) need to get some data to perform a particular operation For example, in the subject, “according to shortage of record file is out of stock” is a process of reading, the arrow from the shortage of “records” to “sales system (statistical) out of stock”

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Fourth, fifth, from the external entity to the processing (input), from the processing to the external entity (output), as mentioned earlier, the external entity is the person or organization outside the software system, is the data source or data endpoint. If it flows into the system from an external entity, the entity is the data source and its operation is the input. If data flows from the system to an external entity, the entity is the data endpoint and the operation is the output. There may be more than one data source or data endpoint. In this case, the system starts with “customer order”. The customer is the data source, and the system needs the customer to “input” the order to the system. The process of processing also to the warehouse, manager, procurement department and other data terminal “output” file processing must have in and out, only in and out, known as the “black hole”; Only out without in, called “miracle”; The current input is not enough to support a certain output (for example, the file ABC is needed to perform an operation, currently only the file AB is passed, but there is output), called “grey hole” these are the basis for completing the “supplement, modify data stream”

Then we will finish the third problem, this kind of problem is a little difficult, the elimination method is not very useful, it is easier to see the “read” and “write” data flow, like the above mentioned “modify inventory record file”, the problem appears twice, but only one data flow points to the file, we can start from there

Let’s start with the question:

“Modify the inventory record file”, the first part is in the first point of the description: “If the inventory goods meet the requirements of the order, the supply process will be carried out, that is, modify the inventory record file”, as shown in Figure 12-7:



The second is in point 3 of the instructions, “Purchase processing according to purchase notice, modify inventory record file”. We add this data flow, starting from “purchase processing” and ending from “Inventory record file”, which is the first supplementary data flow:

Read again note 3, Incoming handling, which consists of 3 operations:

• The first is “modify inventory record file”, which is a “write” operation, and the supplementary data flow has been given above.
• The second is “fetch out of stock order from out of stock record file”, which is the “read” operation;
• Third, it is “supply processing”, which is “from one processing to another processing”

For the second operation, supplement the data flow. Starting point: Out of stock record file, end point: incoming processing

For the third operation, supplement the data flow. Starting point: purchase processing, end point: supply processing

There is still one data stream left to fill in, so let’s look at the problem again and see if there are any hidden Easter eggs. Let’s look at the first sentence of note 1: “Accept customer’s order and check whether stock meets order requirements”. Pat the head, the egg is here! After receiving a customer order, “check the inventory” is not to read the inventory record file? Therefore, a data flow is added, that is, the starting point is the inventory record file and the ending point is the order processing, as shown in the figure:

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The added layer 0 data flow diagram looks like this:

That’s it for the record and HOPEFULLY I can float over the line

The over –