Theory and practice of database design < four > database basic terms and concepts

First, the relationship model

The relational model is one of the most important data models. The relational Database model system uses the relational model as the data organization way.

Data structure of the relational model:

　　relationship : a table

　　tuple : A row of records.

　　Properties : one column

　　code (key, key): A group of attributes in a table that uniquely determines a tuple.

　　domain: A set of values that have the same data type . For example: The age attribute of college students in the domain is (15-45 years old), the gender of the domain is (male, female).

　　component : A property value in a tuple . Each component of a relationship must be a non-divisible data item.

　　Relationship Pattern : A description of the relationship.

　　

　　Candidate Code : If an attribute group in a relationship can uniquely identify a tuple and its subset cannot, the attribute group is called a candidate code .

　　　　Main code : If a relationship has more than one candidate code , select one of them as the main code.

main attribute:　　　　 The candidate main attribute is called the main attribute (primary attribute).

　　　　Non-primary attribute/non-code attribute : A property that is not contained in any candidate code, called a non-primary attribute .

　　　　full code : All the attributes in the relational schema form the candidate code for this relational pattern, which is called a full-size attribute group .

　　　　

"Precautions"

Code/Candidate code/main code/full code: whenever the word "code" is involved, it is the concept of the attribute group, not the concept of a single attribute (single column)!

Theory and practice of database design < four > database basic terms and concepts