Database Paradigm and ER diagram

The database paradigm includes the first, second, third and bcnf paradigm, on the paradigm of the discussion, the blogger in the knowledge to see a very good article, sharing the text, this side will not do the elaboration. Address: https://www.zhihu.com/question/24696366

Here is a list of some of the database definitions:

1. Relational model: a two-dimensional tabular structure represents an entity set, and a foreign key represents a data model of relationships between entities called a relational model. A relational model is a collection of several relational schemas.
2. Relationship mode: The relationship pattern is actually a record type. It includes: schema name, property name, value domain name, and the primary key of the pattern. The relational schema is only a description of the data attributes.
3. Relationship example: A relationship, a two-dimensional table.
4. Properties: In a relational model, a field is called a property.
5. Domain: In a relationship, each attribute has a range of values, called the attribute's domain value.
6. Tuples: In relationships, records are called tuples.
7. Candidate code: The minimum attribute set that uniquely identifies a tuple in a relationship is called the candidate code for the relational pattern.
7. Main attribute: A property that exists in a candidate code (a candidate may be multiple attributes).
8. Main code: The user is selected as a candidate code for the tuple identity.
9. External code: The corresponding property of the main code of a relationship appears in another relationship, at this time the main code is another relationship outside the code, such as there are two relations S and SC, wherein s# is the main code of the relationship s, the corresponding attributes s# in the relationship SC also appear, at this time s# is the relationship SC outside code.

1NF: Property No further points (such as the person has a phone number attribute, there is a string, the use of the first half of the request is a family number, the second half is the company number. does not match 1NF)

2NF: A non-primary attribute directly or indirectly relies entirely on candidate keys. (Cannot partially rely on candidate keys) (non-conforming data redundancy, update exception, insert exception, delete exception)

3NF: The non-primary attribute is directly dependent on the candidate key. (non-conforming data redundancy, update exception, insert exception, delete exception)

BCNF: A non-primary property directly depends entirely on the candidate key, and the primary attribute is directly full function dependent on the key that does not contain it.

The database design can be divided into three steps:

1. Drawing E-r

2. Convert the E-r diagram to a pattern of data (relational mode)

3. Adjust the relationship model according to the paradigm analysis to conform to a certain paradigm

For this design process, bloggers found a few examples in another blog post to help you understand, address: http://wenzongliang.iteye.com/blog/2204577

Database Paradigm and ER diagram