ER model | 程式設計板 | Meteor 學生社群

ER-model : Attributes: simple attribute - atomic values, which cannot be divided further. For example, student's phone number, course ID etc. Composite attribute - made of more than one simple attributes. For example, a student's complete name may have first_name and last_name. Derived attribute - their values are derived from other attributes present in the database. For example, age can be derived from a person's birthday. Single-value attribute - attributes that contain single value. For example - course ID. Multi-value attribute - attributes that contain more single value. For example - a person's phone number. You may have more than one phone number, right? A data can belongs to more than one attributes which is mentioned above can. For example, phone number is a simple attribute. It can also be multi-value attribute. In this case, we say that it is a simple multi-valued attribute. Relationship: One-to-one: One entity from entity set A can be associated with at most one entity of entity set B For example, you are in one of the class in your school. One-to-many − One entity from entity set A can be associated with more than one entities of entity set B however an entity from entity set B, can be associated with at most one entity. For example, a teacher teaches more than one class. Many-to-one − More than one entities from entity set A can be associated with at most one entity of entity set B, however an entity from entity set B can be associated with more than one entity from entity set A. For example, all the teacher who teach the same subject are in the same office. Many-to-many − One entity from A can be associated with more than one entity from B. For example, every student can take more than one course and the course can be taken by many students. Entity : A thing in the real world with an independent existence. For example, students in your school. This picture can help you draw the type of each attributes and relationship. https://i.imgur.com/ywy0lgi.png reference: https://www.tutorialspoint.com/dbms/er_diagram_representation.htm My English is really poor. If there is any mistake about the grammar, please accept my apology.