Database design should be emphasized in the development of large MIS

Since the beginning of 1980s, many computer experts in China have gone deep into some large enterprises and tried to develop the ideal large-sized MIS. Practice has proved that most of the large MIS developed are not ideal. Why? According to my opinion, one of the important reasons is that I did not pay enough attention to the database design of MIS during the development process and did not take it as a top priority. If a large MIS has a problem with its database design, it is a big problem, or fundamentally a problem. This MIS will not succeed, but will only fail. In this case, how should we solve it?
1. The basis of MIS is Database
The NIS system consists of two parts: hardware and software. MIS software is added by documents Program . Its documents are all the design manuals of MIS. Its program is the whole of MIS Algorithm Add the corresponding data structure. The MIS algorithm is nothing more than an algorithm for its various input, modification, query, processing, output, and Menu programs. The data structure of MIS mainly refers to various basic tables in the database design. In this case, the basic table is the basis of MIS. Database design is not only the focus of MIS development, but also the difficulty. It is important because it requires a lot of skills to design a set of basic tables.
MIS is developed in stages. Different stages correspond to different databases. In the initial (initial and extended) stage of MIS, the corresponding database is the application database. The so-called application database is a set of basic tables designed for a specific application. This database is easy to design, use, and maintain. In the intermediate (control and integration) stage of MIS, the corresponding database is the topic database. The topic database is a set of basic tables designed for certain topics. It includes all the application projects within the scope of this topic, the design, use, and maintenance of such databases are complex. In the advanced (data management and maturity) stage of MIS, the corresponding database is a comprehensive database. The so-called integrated database is a set of basic tables designed for the Integrated Management Information System of a large enterprise or a public institution. It includes all topics of the enterprise, the design, use, and maintenance of such databases are complex and require high designers, users, and DBAs.
II. General Database Design Methods
Database design involves five major steps: Database requirement analysis, conceptual design, logical design, physical design, and load testing. The task of requirement analysis is to convert business management documents into data streams, draw a data flowchart DFD, and complete the corresponding data dictionary. The task of conceptual design is to start from DFD, recognize entities and their relationships, and draw an object relationship diagram, that is, a E-R diagram. The task of logical design is to determine the specific attributes of each object and link from the E-R diagram. The physical design task is to determine the type, width, and value range of all attributes, design the primary key and foreign key of the basic table, and apply the English culture of all table names and field names, complete the corresponding data dictionary and create a physical database in a specific DBMS environment. The loading and testing work runs through the whole process of program testing. The entire input, modification, query, processing, and output work can be regarded as the loading and testing of databases. It should be pointed out that the design of large databases is unlikely to be completed successfully once. The above five steps may be a continuous iteration process.
3. Basic tables and other tables
Databases in MIS are composed of a group of basic tables. An entity can be described by a basic table, or a complex link can be described by a basic table. Therefore, a basic table can represent an object or a link. A field in a basic table is an attribute of an object or link. A basic table stores basic data, which has five basic properties. Atomicity, that is, the data in the table is metadata. Attention, that is, the data in the table can generate all the output data of the system. Stability, that is, the data in the table is input at a time, used multiple times, and stored for a long time.
Normalization: The data in the table meets the third paradigm. Objectivity: The data in the table is the data that exists objectively, not the data in subjective imagination.
In addition to basic tables, tables in MIS also have some non-basic tables, such Code Tables, intermediate tables, temporary tables, and virtual tables (Views), which do not belong to the database but all appear in the form of tables, it facilitates data input, query, processing, and output. Using the five properties of a basic table, it is easy to distinguish between a basic table and a non-basic table. The design of non-basic tables is not difficult, and the design of basic tables is difficult. The database design in MIS mainly refers to the design of basic tables.
Iv. Database Design Skills
There are two difficulties in Database Design: one is how to handle the many-to-many relationship, and the other is how to design the primary key. The method for dealing with many-to-many relationships is to break down one many-to-many relationship into one-to-many relationship and add another many-to-one relationship. For example, if there is a many-to-many relationship between two tables, add a table between them. The fields of the table must include at least the primary keys of the first two tables. In this way, a many-to-many relationship is converted into two one-to-many relationships.
In a basic table, a primary key is the unique identifier of a record. Generally, the primary key serves the index file or table connection. It is not transparent to users and is only available to programmers. Therefore, the value of the primary key is preferably a string of non-physical values, and the program automatically adds 1. A primary key is a field permanently non-empty. Once generated, it cannot be modified but can be copied. By copying, the primary key of the table can be used as the foreign key of the table. To design a database, in addition to overcoming the above two difficulties, the following principles should also be followed: the fewer basic tables, the better; the fewer Primary keys, the better; the fewer fields, the better.
V. MIS Development Model
Combined with the characteristics of our country, the development of large MIS and the design of large databases should be divided into two layers, namely the kernel layer and shell layer. The kernel layer corresponds to the rule of law and focuses on versatility in design. The shell layer corresponds to governance, and the design focuses on specialization. With the development of China's economy and the world economy, the core layer of MIS will gradually expand, the shell layer will gradually shrink, and the universality will gradually increase.
At present, the MIS Construction of Large Enterprises and institutions in China has crossed the preliminary stage and started to enter the intermediate or advanced stage. At the same time, the database design has ended the application database period and began to transition to the topic database or integrated database. The Design of theme databases or integrated databases is essentially different from that of application databases: the former is data-oriented, and the latter is program-oriented. MIS Construction of a large enterprise or enterprise is a long-term and repetitive process. In this process, the application and output charts may change year by year, but the basic data remains unchanged. As long as we design the basic table to data-oriented, non-Program-oriented, and organize the metadata with the basic table, we can keep the metadata unchanged to avoid mistakes in MIS Construction.