13 most common database terms

Guidance:This article introducesDatabaseThis article is suitable for beginners who have just begun learning databases. I believe that everyone can find their own needs, so everyone can get what they need.

13 database terms:

1. Relational Model: A two-dimensional table structure is used to represent an object set. A foreign key is used to represent a data model of the association between objects. A relational model is a set of several relational patterns.

2. Link mode: the link mode is actually the record type. It includes mode name, attribute name, Value Domain Name, and mode primary key. The relational mode only describes the data features.

3. Link instance: A link is a two-dimensional table.

4. attribute: in a relational model, a field is called an attribute.

5. Domain: In a link, each attribute has a value range, which is called the value range of an attribute.

6. tuples: records are called tuples in a link.

7. Candidate Code: The property set that uniquely identifies a tuples in a link is called the candidate code of the link mode.

8. Primary code: A candidate code selected as the primary code for the tuples.

9. external code: the corresponding attribute of the primary code of a link appears in another relational system. In this case, the primary code is an external code of another link. If there are two relationships: S and SC, S # is the master code of link S, and the corresponding attribute S # also appears in the Link SC. In this case, S # is the external code of the link SC.

10. entity integrity rule: This rule requires that the element group in the link cannot have null values on the attribute that constitutes the master code. If a null value exists, the primary code value cannot uniquely identify the tuples.

11. Reference integrity rules: This rule requires "no reference to nonexistent entities ". The format is defined as follows: If attribute set K is the primary code of the relational model R1, and K is also the external code of the relational model R2, then in the relationship of R2, the value of K can only be null or equal to a primary code value in the R1 relationship.

Note the following when using this rule:

(1) The external code and the corresponding primary code can have different names, as long as they are defined on the same value range.

(2) R1 and R2 can also be in the same link mode, indicating the relationship between attributes.

(3) Whether the external code value is allowed to be empty depends on the specific problem.

12. Procedural language: the procedure for obtaining results must be provided during programming, that is, "What" and "how to do ". Such as Pascal and C.

13. Non-Procedural language: During programming, you only need to specify the required information. You do not need to set up a language for specific operation steps. All relational query languages are non-procedural languages.