五范式（Five normal form）.docVIP

五范式（Five normal form） Detailed database paradigms: the third paradigm and the fifth paradigm, 2009, 01, Friday, 16, 8:53 A.M.1NF: a column in table is not divisible (i.e., atomicity of columns) 2NF: a line in table is uniquely marked (that is, rows in table cannot be duplicated) 3NF: does a column in table not depend on a column that is not a primary key in another table, or is it not popular?! Great cold!! For example: there is a department of table, we call it tbl_department, it has so few columns (dept_id (PK), dept_name, dept_memo...) There is a staff table, we call it tbl_employee, in this table there is a column of dept_id (FK) describes information about the Department, if tbl_employee to meet 3NF, In tbl_employee, there are no other columns of information about the dept_id column! The design of a general database satisfies 3NF! (personally think it should be possible to meet the 3NF statements of a school, ^_^) BCNF: BCNF is generally considered to be the revised third paradigm, which is further than 3NF! 4NF: 5NF: divide a table into smaller chunks as much as possible to exclude all redundant data in the table Paradigm introduction To answer these questions, it is important to understand the difference between 3NF, BCNF, 4NF, and 5NF. The following is an exact definition of each paradigm. First paradigm (1NF) Each table must have a primary key, that is, the minimum set of attributes, which correspond to each record one by one. By properly defining key attributes and non key attributes, duplicate groups are deleted (different records seem to require different repetitions of data types). Note: each property must contain a single value, not a set of values. The second paradigm (2NF) The database must meet all the requirements of 1NF. In addition, if a table has a compound key, all attributes must be associated with the entire key. Also, between rows of tables, redundant duplicate data is moved in a separate table. The third paradigm (3NF) The data stored in th