Database Background SQL


A database is a structure that contains information about many different categories of information and about the relationships between these categories. There are some terms and concepts that are important for you to know in the database environment. For instance, the term entity, attribute, and relationship are fundamental when discussing databases. An entity is a person, place, object, event, or idea for which you want to store and process data.

An attribute is a characteristic or property of an entity. The term is used in this text exactly as it is used in everyday English. For the entity person, for example, the list of attribute might include such things as eye color and height. An attribute is also called a field or column in many database system.

The final key term is relationship. A relationship is an association between entities. There is an occasion between Student and Course, for example, at the ERD above. A course is associated to all of the students, and a student is associated with their course. Technically, you say that a course is related to all of his/her students, and a student is related to their course.

This particular relationship is called one-to-many relationship because each course is associated with many student, but each student is associated with only one course. In this type of relationship, the word many is used differently than in everyday English; it might not always indicate a large number. In this context, for example, the term many means that a course can be associated with any numbers of students. That is, a given course can be associated with zero, one, or more than one students.
Database definition: A database is a structure that can store information about multiple types of entities, the attribute of those entities, and the relationships among the entities.


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