Another chapter is over——Chapter 6 Relational Data Theory. The homework in this chapter is quite brain-intensive.
First review the four paradigms
1NF: It is the basic requirement for the relational model. A database that does not meet the first normal form (1NF) is not a relational database. The first normal form (1NF) means that each column of the database table is an indivisible basic data item, and there cannot be multiple values in the same column, that is, an attribute in an entity cannot have multiple values or duplicate attributes. In short, no duplicate columns.
2NF: If R ∈ 1NF, and each non-key attribute is fully functionally dependent on any candidate key, then R ∈ 2NF.
3NF: Let the relational pattern R<U,F>∈ 1NF, if there is no such code X in R, attribute group Y and non-attribute group Z ( Z ⊉ YZ \nsupseteq YZ⊉Y ) makesX→Y,Y→Zholds,Y↛X, then it is calledR<U,F>∈3NF.
BCNF: Relational schema R<U, F>∈ 1NF, if X → Y and Y ⊈ XY \nsubseteq XY⊈When X, X must contain a code, thenR<U,F>∈BCNF. That is, in R, every determinant contains codes.
A relational schema that satisfies BCNF is:
All nonprimary attributes are fully functionally dependent on every key
All primary attributes are also fully functionally dependent on every key that does not contain it
No attribute is fully functionally dependent on any set of attributes that are not key.
4NF: Relational pattern R<U, F> ∈ 1NF, if for each nontrivial multivalued dependency X →→ Y ( Y ↛ X ) of R, X contains a code, then R<U, F> ∈ 4NF. Non-trivial and non-functional multivalued dependencies are not allowed between attributes of a restricted relational schema.
The homework is as follows, handwriting, taking pictures and uploading, three consecutive operations? Ignore the word couchou. .
The homework question is 2 6 7 8
