Detailed explanation of soft exam afternoon questions --- data flow diagram design, soft exam Data Flow

Detailed explanation of soft exam afternoon questions --- data flow diagram design, soft exam Data Flow

Five main questions in the afternoon of the soft exam over the years are data flow diagram design, database design, uml diagram, algorithm, and design pattern. Starting from today's blog, I want to share with you the content of the soft exam afternoon questions, including theoretical knowledge and explanations of typical examples, we can do better. Today, we will briefly summarize the knowledge about the data flow diagram. First, let's look at the figure below:

Next, the editor will follow the context of the Mind Map above and explain in detail the data flow chart in the soft exam in sequence. If you have different opinions, you are welcome to discuss and exchange, first, let's look at the first basic knowledge point:

Basic symbol of a data flow chart

A Data Flow Diagram (DFD) is a graphical tool used to describe the Data processing process, from the perspective of data transmission and processing, she graphically describes the process of data flow in the system flow and the transformation of the processed changes. It reflects the data flow, natural logical processes, and necessary logical data storage. Let's take a look at the following table. In the data flowchart, there are mainly the following symbols:

As we have shown, in a data flow diagram, four basic data flow diagram symbols are usually used. In any data flow diagram, four basic symbols must be included, which are indispensable. The first symbolic circle indicates the processing process, in which the processing name and number are indicated. The second signed Arrow: the name of the data stream written above, so the same data stream may have different processing results after processing, for example, the flour in daily life, after processing, it may be processed into steamed bread or flour. The main function is to process the data stream. If there is a stream, there will be an outflow. On the same data flow diagram, there cannot be a data stream with the same name, if there are more than two Data Streams pointing to one processing. Or when two data streams are output in a processing process, there is often a certain relationship between these data streams. The relationship is as follows:

Third symbol: data storage file: it is usually represented by a dual horizontal line, but the representation of the data storage file is different in different teaching materials. For example, it is represented by a double horizontal line or a half-framed line. The arrow indicates the process of saving or removing the line, indicating the process of reading and writing. Generally, the file name is written in the middle, A data storage file is used to save data. It can be a database file or another form of data organization. Therefore, its flow can be understood as a query file. The arrows can be understood as the expected results.
Symbol 4: Data Source point or sink point, indicating the source of the data input to be processed in the data flow diagram. In a data flow diagram, it is just a symbol and does not need to be designed and implemented in any software way. She is an entity in the external part of the system, so she is called an external entity. Generally, this type of data source or sink only appears in the top-level diagram of the data flow diagram. After learning the basic symbols of the data flow diagram, let's take a look at the design principles of the data flow diagram:

Data Flow diagram design principles

The design principles of the data flow diagram are described in the following typical examples.

Data Dictionary

A Data Dictionary defines and describes data items, data structures, data streams, data storage, processing logic, and external entities, the purpose is to give a detailed description of each element in the data flow chart. Data dictionary is a directory that you can access to record the original Data of databases and applications. An active data dictionary is a data dictionary that can be automatically updated by the DBMS when the database or application structure is modified. A passive data dictionary is a data dictionary that must be updated manually when being modified. Let's take a look at the figure below:

After introducing the basic theoretical knowledge of the data flow diagram, we will start to practice. Here we will give two simple examples to consolidate the previous theoretical knowledge, first of all, let's look at a real question in March January. Although the question in the 04 years has been around for a certain period of time, the questions in the soft exam are not changed, as a result, I have mastered the basic problem-solving methods and skills, and have never changed my mind. I am always right. Well, I will not talk about it. The question is as follows:

Typical Example:

The data flow chart is as follows:

The problem is as follows:

After obtaining the questions, we need to carefully read the questions several times, because the question is not difficult, the key is to be careful. Sometimes, a sentence in the question may be the answer we need. First, let's take a look at the first question. The question says that two data streams in Figure 2 are incorrect. Please point out the endpoints and starting points of the two data streams. Let's analyze them, the four input management work request sheets, query request information, reader information, and current date in the top-layer graph are all displayed. Next, let's look at the output, the output information includes the information about books, readers, and illegal requests. In the 0-layer diagram, both the book situation and the reader situation are reflected, however, we will find that illegal request information is output in the top-layer graph. In the layer-0 graph, there are two illegal management work request tickets and illegal query request information, respectively, however, we cannot determine whether this is an error. In this case, an output stream in the top-layer graph may be broken down in the layer-0 graph. Let's put it for now. Next, let's look at the reader file. Processing the query request is a process of writing the reader file, and registering the reader information is to write or retrieve the reader file. First, let's take a look at processing the query request. From the previous event description, we can see that the query request contains the query of books and readers. The output result is correct, it also corresponds to the top-level chart. During the query process, based on the user's query request information, if you want to query the information of the system analyst's continue guide, the system analyst's continue guide will be entered, then, the output is the system analyst's continued guidance on the book, the author, the price, the publishing house, and so on. So there is no input here, so for reader files, some of the information she borrowed should be input in the opposite direction. After receiving the query information, she will retrieve the relevant records from the reader file for query. In the same case, the third processing, register the reader information. The reader information is input, and no output is made. In violation of the Data conservation rules, output is required for input. If there is input, there should be output after processing. What is output, nie? Here, the reader information is entered. The processing function is to register the reader information, where to register the reader information, which should be included in the reader file, so it should be in the opposite direction, as shown below:

Therefore, the answer to the first question is from 2 to the reader file, from the reader file to 3. This question examines the principle of balance between subgraphs and parent graphs. Let's take a look at the second question:

The third data flow diagram is a refinement of the second processing of the 0-layer diagram. The second processing is refined into reader information query and book information query, so we need to find the missing data flow, we first use the principle of balancing the parent and subgraphs. First, let's look at the data flow corresponding to the Layer 1 diagram and the layer 1 diagram.
First, enter: query the request information. The input of the reader file outputs three items: Book information, reader information, and illegal query of the reader request information. What is missing should be the internal data flow, because the query request information includes two types: one is to query the reader request information, and the other is to query the library request information, which is also divided into two types, therefore, the data stream is balanced with the parent graph, but the problem is that there are three fewer data streams, and the three fewer data streams are there? According to the principle of balance between subgraphs and parent graphs, what is missing must be between 2.1 and 2.2, or between 2.1 and 2.2 and files.

So here, we need to find the corresponding answer based on the description of the questions. The questions are described as follows: the system's information query function mainly includes reader information query and book information query, the reader information query can obtain the basic information of the reader and the information about the reader borrowing the book. The basic information of the book and the lending status of the book can be obtained by querying the book information. Based on the description of the questions, it is easy to see that the document for borrowing books should be used for information query of readers, because the document for borrowing books is required, and the information for borrowing books is included in the document for borrowing books, therefore, if you need to query the reader information, you must not only have a reader file but also borrow a book file. Therefore, you need to add a data stream from the End file to the reader information query. In the same case, we also need to add a data stream from the borrowing file to the query of the book information. Besides the basic information about the book, it should also include the borrowing of the book, so she is also in the borrowing file, at the same time, let's look at the borrowing situation of books, so we also need to query the data stream from the book directory file to the book information, because the basic situation of the books to be queried is in the book directory file, so we can find the missing data stream based on the test description. Both can be determined based on the principle of balance between the subgraph and the parent graph, as well as the description of the questions. Next, let's look at the third question:

Brackets indicate repeated situations. Management includes four aspects: purchasing new books, borrowing books, returning books, and canceling books. When purchasing a new book, you need to prepare a warehouse receiving ticket for the book. When you borrow a book, you need to fill in the borrow ticket. You need to fill in the return ticket when returning the book. When canceling a book cancellation, you must enter the cancellation form. Therefore, her management work request includes four types of situations: warehouse receiving, borrowing, returning, and deregistering, because the four types are optional, according to the description of the data structure in the data flow diagram, we should use brackets and separate them with a vertical line in the middle. Let's take a look at the warehouse receiving Ticket: Let's take a look at the question description. The content of the warehouse receiving ticket includes the book category directory number, title, author, price, quantity, and sufficient date. Is this clear about nie.

Small message: In this blog post, I will explain the data flow diagram of the afternoon Question of the test site in the soft exam. I will explain the basic content in four aspects, the basic symbols of the data flow diagram, and the design principles of the data flow diagram, the data dictionary then lists a simple example to consolidate the previous theoretical knowledge. Although the question of 04 years has been a bit old, the questions of the soft exam are not changed, as a result, I have mastered the basic problem-solving methods and skills, and have never changed my mind. For data flow charts, the key is to be careful, the answer information we need is highlighted in the eye. Generally, when solving the problem, we will use the balance principle between the top subgraph and the parent graph. We already have the data balance principle and have a good understanding of the question skills, the data flow diagram is the question of delivery. Believe in yourself, there is certainly no problem. Since the last small series was studying with a cool mindset, I felt that this time, but next time, I was able to complete the small series. It doesn't matter. The smaller the small series will be, the more brave it is, and the more I embrace the soft test, let's wait and see what a miracle will the mini-Editor bring to you.