In-depth analysis of converting conceptual model into relational model

Conceptual model and relational model are two models commonly used in database design. The conceptual model is used to describe the conceptual relationships between entities, while the relational model is used to describe the relationships between the data actually stored in the database. In database design, it is usually necessary to convert the conceptual model into a relational model, which is an important process. This process includes converting entities in the conceptual model into tables in the relational model, and converting relationships in the conceptual model into foreign key constraints in the relational model. Through this process, it is possible to ensure that the structure of the database is consistent with the relationship between the conceptual model, thereby achieving effective storage and query of data.

The process of converting a conceptual model into a relational model mainly includes the following steps:

1. Identify entities and attributes

Entities in the conceptual model represent independently existing things, such as people, items, events, etc. In addition to identifying the entity, it is also necessary to determine its attributes, such as the person's name, age, gender, etc.

2. Determine the relationship between entities

In the conceptual model, there may be different relationships between different entities, such as a person You can have multiple items, or an event can include multiple people, etc. Therefore, after determining the entities and attributes, it is also necessary to determine the relationships between entities and convert them into tables and fields in the relational model.

3. Determine the structure of the table based on entities and relationships

After determining the entities and relationships, you need to design the database tables based on this information structure. Normally, each entity corresponds to a table, which contains all attributes of the entity. If there are relationships between multiple entities, you need to use foreign keys to establish connections between tables.

4. Design the relationship between tables

After determining the structure of the table, you need to design the relationship between different tables. If there is a one-to-many relationship between two tables, you need to add a foreign key in the more table to point to the primary key of the other table. If there is a many-to-many relationship between two tables, an intermediate table needs to be used to connect them.

The above are the main steps for converting a conceptual model into a relational model. The methods and examples of these steps are introduced below.

1. Identify entities and attributes

When identifying entities and attributes, you need to clearly understand the business requirements and conduct Analysis and classification. Entities and attributes are usually divided into three levels: entities, attributes, and relationships.

Taking the student information management system as an example, we can identify the following entities and attributes:

Student: name, gender, age, class

Subject: name, number

Course: name, number, subject

Achievements: Students, courses, scores

2. Determine the relationship between entities

When determining the relationship between entities, different entities need to be considered The types of relationships between them, such as one-to-one, one-to-many, many-to-many, etc., and it is also necessary to consider whether these relationships are directional.

Taking the student information management system as an example, we can identify the relationship between the following entities:

① Between students and classes One-to-many relationship, that is, a class can have multiple students, but a student only belongs to one class.

② There is a one-to-many relationship between subjects and courses, that is, a subject can have multiple courses, and a course only belongs to one discipline.

③ There is a one-to-many relationship between students and grades, that is, a student can have multiple grades, and one grade only belongs to one student; there is also a one-to-one relationship between courses and grades Multiple relationships, that is, a course can have multiple grades, but a grade only belongs to one course.

3. Determine the structure of the table based on entities and relationships

When determining the structure of the table, you need to design the table based on entities and relationships. structure and identify the fields contained in each table.

Taking the student information management system as an example, we can design the following table structure: Student table (Student): contains the student’s name, gender, age, class and other fields, where the class field is as Foreign key, pointing to the primary key of the class table.

Class table: Contains the class name, grade and other fields, as well as a self-increasing primary key ID field.

Subject table: contains fields such as subject names, numbers, and a self-increasing primary key ID field.

Course table: Contains fields such as course name and number, as well as subject fields as foreign keys, pointing to the primary key of the subject table, and also contains a self-increasing primary key ID field.

Grade table: Contains fields such as students, courses, scores, etc., where the student and course fields are used as foreign keys, pointing to the primary keys of the student table and course table respectively, and also contains an auto-increment The primary key ID field.

4. Design the relationship between tables

When designing the relationship between tables, it needs to be established based on the relationship between entities Links between tables usually use foreign keys to establish links between tables.

Taking the student information management system as an example, we can establish the following connections between tables:

①The connection between the student table and the class table: Add a class field as a foreign key in the student table, pointing to the primary key ID field of the class table.

②The connection between the subject table and the curriculum: Add a subject field as a foreign key in the curriculum, pointing to the primary key ID field of the subject table.

③The connection between the student table and the grade table: Add a student field as a foreign key in the grade table, pointing to the primary key ID field of the student table.

④The connection between the course schedule and the grade table: Add a course field as a foreign key in the grade table, pointing to the primary key ID field of the course table.

Through the above steps, we can convert the conceptual model into a relational model and design a database structure that meets the needs.

It should be noted that when designing a relational model, data integrity and consistency issues also need to be considered. For example, in the above-mentioned student information management system, the primary key ID of the class table should be unique, the class field in the student table should only refer to the primary key ID that already exists in the class table, and the student and course fields in the grade table should only reference Can reference existing primary key IDs in the student table and course table. These can be achieved by setting foreign key constraints. In addition, you can also ensure the integrity and consistency of data by setting unique constraints, non-null constraints, default value constraints, etc.

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