Table of contents
Chapter 12, Data Flow Diagram (DFD)
1. Basic concept of data flow diagram
A data flow diagram is a tool for representing a logical model of a system. from the datadelivery and processingFrom the point of view, graphically describe the process of data flow and processing in the system
2. Data dictionary
Data dictionary refers to the definition and description of data items, data structure, data flow, data storage, processing logic, etc., and its purpose is toMake a detailed description of each element in the data flow diagram, using a data dictionary for simple modeling projects
Ticket = name + date + flight number + origin + destination + fare
FlightNumber = "Y7100" ... "Y8100"
End point=[Changsha Shanghai|Beijing|Xi'an]
3. Data balance principle
Balance between parent graph and child graph
subgraph balance
4. Data flow diagram test problem-solving skills
Detailed analysis of test questions
数据管理员available through middlewareUser management, operation management and authority management. User management maintains user information, user information (username, password) is stored in the user table ; operation management maintains the standard operations of data entities and their belongings 后端数据库信息, standard operations and back-end database information are stored in the operation table ; authority management maintains authority A table that stores information about actions that users can perform.
√The data administrator is an external entity;
√There are processes such as "user management", "operation management" and "authority management" in the middleware
; Management”;
√The back-end database is an external entity;
√There is a data store called “Operation Table” in the middleware, and this store is related to “Operation Management”;
√ There is a data store called “Permission Table” in the middleware, and This storage is related to "Rights Management".
Utilize the principle of data balance
4.1. Question 1
Read the following instructions and diagrams, answer questions 1 to 4, and fill in the answers in the corresponding columns on the answer sheet. [Description] In order to centrally manage and control users' access to data and support a large number of connection requirements, the data center of a large enterprise wants to build a data management middleware. Its main functions are as follows: (1) It can be implemented through
the 数据管理员middlewareUser management, operation management and authority management. User management maintains user information, user information (username, password) is stored in the user table ; operation management maintains the standard operations of data entities and their 后端数据库information, standard operations and back-end database information are stored in the operation table ; authority management and maintenance Permission table , which stores information about operations that users can perform.
(2) The middleware verifies 前端应用the user information provided. If the verification fails, return illegal user information; if the verification passes, the middleware will wait for the front-end application to submit an operation request.
(3) After the front-end application submits the operation request, if the user does not have the right to perform the operation, return the insufficient permission information, otherwise, perform connection management.
(4) Connection management Connect to the corresponding background database and submit the operation. Connection management first checks whether there is an idle database connection, if not, create a new connection; if it exists, reuse the connection.
(5) The back-end database performs operations and transmits the results to the middleware, and the middleware processes the received operation results and returns them to the front-end application.
Now use the structured method to analyze and design the system, and obtain the top-level data flow diagram shown in Figure 11-1 and the 0-level data flow diagram shown in Figure 11-2.
[Question 1] (3 points) Using the words in the description, give the names of entities E1~E3 in Figure 11-1.
Front-end application, data administrator, and back-end database
[Question 2] (3 points) Use the words in the description to give the names of the data stores D1~D3 in Figure 11-2.
User table, operation table, permission table
[Question 3] (6 points) Give the name of the processing P in Figure 11-2 and its input and output streams.
Operation results, E3 (back-end database)
processed operation results, E1 (front-end verification)
In addition to processing the input and output streams of P, two data streams are missing in Figure 11-2, please give these two data streams start and end points.
D2, authority verification
D3, authority verification
Note: The vocabulary in the name usage instructions, the starting point and the ending point all use the symbols or vocabulary in Figure 11-2.
[Question 4] (3 points) When drawing a data flow diagram, you need to pay attention to the drawing of processing. Please give three kinds of errors that may occur when drawing the input and output of processing.
1. Processing has only input but no output
. 2. Processing has only output but no input.
3. Input stream and output stream have the same name
. 4. It is impossible to generate output stream after input stream is processed.
4.2. Question 2
Read the following description and data flow diagram, answer questions 1 to 4, and fill in the answers in the corresponding columns on the answer sheet.
[Description]
Now we are planning to develop a credit card management system CCMS for a certain bank. The basic functions of the system are:
1. Credit card application . 非信用卡客户Fill in the credit card application form, explain the type of credit card to be applied for and the basic information of the applicant, and submit it to CCMS. If the credit card application is 银行accepted, CCMS will record the basic information of the customer and sendConfirmationTo the customer, inform the customer of the validity period and credit limit of the credit card; otherwise the customer will receive arejection letter. Non-credit card customers become credit card customers after receiving the confirmation letter.
2. Credit card activation . The credit card customer submits an activation request to CCMS, and activates the credit card with the credit card number and password. After the activation operation is completed, CCMS willActivation notificationSent to the customer to let them know if their credit card was successfully activated.
3. Credit card customer information management . credit card customerspersonal informationCan be managed online in CCMS. Every credit card customer can onlineQuery and modify personal information.
4. Transaction information query . 信用卡客户Every transaction made with a credit card is recorded in CCMS. Credit card customers can inquire and verify theirTrading Information(including credit card transaction records and transaction amount).
Figure 11-3 and Figure 11-4 respectively give the first draft of the top-level data flow diagram and the 0-level data flow diagram of the system.
【Question 1】(3 points) According to 【Instruction】, fill in E1～E3 in Figure 11-3 completely.
Non-credit card users, credit card users, and banks
[Question 2] (3 points) Three data streams are missing in Figure 11-3. According to [Description], point out the starting point and end point of these three data streams. (Note: The start and end points of the data flow use the symbols and descriptions in the figure)
E1 to p0 credit card application form
E2 to p0 activation request
E2 to p0 transaction information
[Question 3] (5 points) There are two items in Figure 11-4 The data stream is wrong, please point out the names of these two data streams and correct them. (Note: The start and end points of the data flow use the symbols and descriptions in the figure)
Credit card application form, activation request
p4 Credit card application form E1
E2 activation request p3
[Question 4] (4 points) According to [Description], convert Figure 11- Fill in the processing names of P1~P4 in 4 completely.
Transaction information query, credit card customer information management, credit card activation, credit card application
