DATABASE NORMALIZATION

Normalization - ObjectivesTable should contain subject wise data.Minimum controlled redundancy.To eliminates redundancy.To eliminates dependency.

Data RedundancyData redundancy is less desirable in database environment.Data redundancies yield the update, insert and delete anomalies.

Update AnomalyAnupdate anomaly. Employee 519 is shown as having different addresses on different records

E_IDE_ADDRSKILL42687 Sycamore GroveTyping42687 Sycamore GroveShorthand51994 Chestnut StreetPublic Speaking51996 Walnut AvenueCarpentry

Insert AnomalyAninsertion anomaly. Until the new faculty member, Dr. Newsome, is assigned to teach at least one course, his details cannot be recorded.New Record ?

Faculty_IDFaculty_NameFaculty Hire DateCourse Code389Dr. Giddens10-Feb-2013ENG-206407Dr. saperstein15-JAN-2012CMP-101407Dr. saperstein15-JAN-2012CMP-201

424Dr. New Son29-MAR-2012

Delete AnomalyAdeletion anomaly. All information about Dr. Giddens is lost if he temporarily ceases to be assigned to any courses..

Faculty_IDFaculty_NameFaculty Hire DateCourse Code389Dr. Giddens10-Feb-2013ENG-206407Dr. saperstein15-JAN-2012CMP-101407Dr. saperstein15-JAN-2012CMP-201

Normalization- definitionsFunctional Dependency An attribute A determines attribute B then attribute B is functionally dependant on attribute A. A B Eg. Student(sid, sname, marks) sid sname, sid ? marks sid functionally determined sname

Normalization- definitionsGeneralized functional dependency attribute A determines attribute B if all of the rows in the table that agree in value for attribute A also agree in value for attribute B.

Normalization-definitionsFully functionally dependency If attribute B is functionally dependant on a composite key A but not on any subset of that composite key, the attribute B is fully functionally dependant on A.

Normalization-definitionsTrivial functional dependency A trivial functional dependency is a functional dependency of an attribute on a superset of itself.

{Employee ID, Employee Address} {Employee Address} is trivial,

Normalization-definitionsTransitive dependency Atransitive dependencyis an indirect functional dependency, one in whichXZonly by virtue ofXYandYZ. Multivalued dependency Amultivalued dependencyis a constraint according to which the presence of certain rows in a table implies the presence of certain other rows.

Normalization-definitionsJoin dependency A tableTis subject to ajoin dependencyifTcan always be recreated by joining multiple tables each having a subset of the attributes ofT.Super key Asuperkeyis a combination of attributes that can be used to uniquely identify a database record. A table might have many superkeys

Normalization-definitionsCandidate key Acandidate keyis a special subset of superkeys that do not have any extraneous information in them: it is a minimal superkey.A table with the fields , , and has many possible superkeys. Three of these are , and . Of those, only is a candidate key as the others contain information not necessary to uniquely identify records ('SSN' here refers to Social Security Number, which is unique to each person).

Normalization-definitionsNon-prime attribute A non-prime attribute is an attribute that does not occur in any candidate key. Employee Address would be a non-prime attribute in the "Employees' Skills" table. Prime attribute A prime attribute, conversely, is an attribute that does occur in some candidate key.

Normalization-definitionsPrimary key One candidate key in a relation may be designated theprimary key. While that may be a common practice (or even a required one in some environments), it is strictly notational and has no bearing on normalization. With respect to normalization, all candidate keys have equal standing and are treated the same.

NORMAL FORMSFIRST NORMAL FORM (1NF).SECOND NORMAL FORM (2NF).THRID NORMAL FORM (3NF). BOYCE-CODD NORMAL FORM (BCNF).FOURTH NORMAL FORM (4NF).

1NFCHARACTERISTICSTable Format.No Multi valued attribute. Primary Key Identified.

2NFCHARACTERISTICS1 NF.No Partial Dependency.

3NFCHARACTERISTICS2 NF.No Transitive Dependency.

BCNFCHARACTERISTICSSpecial Case of 3NF.Every determinant is a candidate key.

4NFCHARACTERISTICS3NFNo independent multi valued dependencies

CONVERSION TO 1NF Assume a video library maintains a database of movies rented out. Without any normalization all information is stored in one table as shown.

Here Movies Rented column has multiple values

CONVERSION TO 1NF (Cntd)1NF: Each table cell should contain single value and Each record needs to be unique

CONVERSION TO 1NF (Cntd)Hence we require both Full Name and Address to uniquely identify a record. This is a composite key. So primary key is identified.

Assignment

If a table project has the information about the projects and employees as shown.Project (proj_num, proj_name, emp_num, job_class, chg_hour, hours); A group of employees are assigned to a given project. an employee can be assign to different projects.Each employee charges according to his job class.Then Convert the table in to first normal form?

CONVERSION TO 2NF2NF RulesRule 1- Be in 1NFRule 2- Single Column Primary Key (no partial dependency) .

CONVERSION TO 1NF The primary key PK=proj_num+emp_numDependenciesProj_num,emp_num proj_name,emp_name,job_class,chg_hour,hoursProj_num proj_nameEmp_num emp_name,job_class,chg_hourJob_class chg_hour

Conversion to 1 NF (cntd..)1NF(Proj_num,emp_num proj_name,emp_name,job_class,chg_hour,hours)

Partial dependencyProj_num proj_nameEmp_num emp_name,job_class,chg_hour

Transitive Dependency Job_class chg_hour

Conversion to 2 NF(cntd ..)Key Components proj_num Emp_num proj_num and emp_numAssigning dependent attributeproject( proj_num, proj_name)Employee(emp_num, emp_name,job_class,chr_hour)Assignment(proj_num,emp_num,assign_hours)

Conversion to 3 NF3NF RulesRule 1- Be in 2NFRule 2- Has no transitive functional dependencies

Conversion to 3 NF (Cntd..) Transitive dependency in the given project table Job_class chg_hour Remove the dependent attribute project( proj_num, proj_name)Employee(emp_num, emp_name,job_class) Job(Job_class, chg_hour)Assignment(proj_num,emp_num,assign_hours)