Cdac original post part-3 for cdac mohali,cdac trivandrum,cdac pune,cdac hyderabad,noida and bangalore and recruitment from cdac.
Let me tell you before you go for this presenation how is the placement and recruitment in cdac going on.
I know about cdac hyderabad for cdac dabc its almost 100% and dac pune has around 80% ,desd pune has around 60% and desd hyderabad recruitment 70%.
Rest please you can enquire these things from orkut communities for 2010 created.Here i am going on Data Normalization
Normalization
Database normalization is a technique for designing relational database tables to minimize duplication of information and to safeguard the database against certain types of logical or structural problems, namely data anomalies
Objectives
Data normalization aims to derive at records which avoid ?
Repetition of Data
Update anomalies
Insert Anomalies
Delete Anomalies
The Process of Normalization
Usually three steps (in industry) giving rise to
First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
In academia
Boyce -Codd Normal Form (BCNF)
Fourth Normal Form (4NF)
Steps in Data Normalization
Attributes - Repeating Groups
When a group of attributes has multiple values then we say there is a repeating group of attributes in the entity
Functional Dependency
Consider a relation R that has two attributes A and B. The attribute B of the relation is functionally dependent on the attribute A if and only if for each value of A no more than one value of B is associated.
In other words, the value of attribute A uniquely determines the value of B
Stud_id -> stud_name
Stud_id -> Date of Birth
Module_id -> Module name
Marks -> grade
Full Functional Dependency
Let A and B be distinct collections of attributes from a relation R B is then fully functionally dependent on A if B is not functionally dependent on any subset of A.(Stud_id, Module_id) -> marks
First Normal Form
A relation is in 1NF if and only if every attribute is single valued for
each tuple or row.
A relation is in 1NF if and only if there are no repeating groups of
Attribute values.
Example of First Normal Form
PURCHASE-ORDER (ORDER#, SUPPLIER#, ORDER-DATE
DELIVERY-DATE, (PART#, PART-DESCRIPTION,
QUANTITY-ORDERED, PRICE), TOTAL-PRICE)
Example in 1NF
PURCHASE-ORDER (ORDER#, SUPPLIER#, ORDER-DATE
DELIVERY-DATE, TOTAL-PRICE)
PURCHASE-ITEM-1 ( ORDER#, PART#, PART-DESCRIPTION,
QUANTITY-ORDERED, PRICE)
Example
STUDENT (Student#, student-name, student-address)
ENROLMENT (Student#, Course#, course-title,
tutor-name,tutor-staff#
1st Normal Form
Process results in separation of different objects
BUT anomalies may still exist
PURCHASE-ITEM-1( ORDER#, PART#, PART-DESCRIPTION,QUANTITY-ORDERED, PRICE)
PART-DESCRIPTION appears on every PURCHASE-ITEM occurrence.
This may result in anomalies when updating or deleting records
The problem in the example is that PART-DESCRIPTION is functionally dependent only on PART# (part of the identifier)
Second Normal Form
A relation is in 2NF if and only if it is in 1NF and all the
non-key attributes are fully functionally dependent on the
key.
Any entity type in 1NF is transformed to 2NF
Identify functional dependencies
Re-write entity types so that each non-identifying attribute is functionally dependent on the whole of the identifierExample
PURCHASE-ORDER (ORDER#, SUPPLIER#, ORDER-DATE
DELIVERY-DATE, TOTAL-PRICE)
PURCHASE-ITEM-1 ( ORDER#, PART#, PART-DESCRIPTION,
QUANTITY-ORDERED, PRICE)
Functional Dependencies
PURCHASE-ORDER (ORDER#, SUPPLIER#, ORDER-DATE
DELIVERY-DATE, TOTAL-PRICE)
PURCHASE-ITEM-1 ( ORDER#, PART#, PART-DESCRIPTION,
QUANTITY-ORDERED, PRICE)
In 2nd Normal Form
Decompose PURCHASE-ITEM into two entity typesPURCHASE-ITEM (Order#, Part#, Quantity-Ordered, Price)
PART (Part#, Part-Description)
Original entity types are decomposed into three entity types in 2nd normal form
PURCHASE-ORDER (Order#,Supplier#, Order-Date, Delivery-Date, Total-Price)
PURCHASE-ITEM (Order#, Part#,Quantity-Ordered, Price)
PART (Part#, Part-Description)
Example in 2NF
STUDENT (Student#,Student-Name, Student-Address)
ENROLMENT ( Student#, Course#, Tutor-Name, Tutor-Staff#)
COURSE (Course#, Course-Title)
Third normal Form
A relation is in 3NF if and only if it is in 2NF and nonon-key attribute is transitively dependent on the key.
Any enity type in 2NF is transformed in 3NF
Determine functional dependencies between non identifying attributesDecompose enity into new entities
Example
STUDENT (Student#,Student-Name, Student-Adderss)
ENROLMENT ( Student#, Course#, Tutor-Name, Tutor-Staff#)
COURSE (Course#,, Course-Title)
Functional Dependencies
STUDENT (Student#,Student-Name, Student-Adderss)
ENROLMENT ( Student#, Course#, Tutor-Name, Tutor-Staff#)
COURSE (Course#,, Course-Title)
Example in 3NF
STUDENT (Student#,Student-Name, Student-Adderss)ENROLMENT ( Student#, Course#, Tutor-Staff#)
COURSE (Course#,, Course-Title)
TUTOR (Tutor-Staff#, Tutor-Name)
Example of Normal Forms
Functional Dependencies
Analysis of the sample FDs1NF: Since PROGNAME and EMPID is the composite key, each cell contain single value so WORK is in 1NF.
The partial dependencies are
PROJNAME PROJMGR, BUDGET, STARTDATE
EMPID EMPNAME, SALARY, EMPMGR, EMPDEPT
Transform the relation work into an equivalent collection of 2NF relations
The relations schemes are:
PROJ ( PROJNAME, PROJMGR, BUDGET, STARTDATE)
EMP ( EMPID, EMPNAME, SALARY, EMPMGR, EMPDEPT)
WORK1 ( PROJANAME, EMPID, HOURS, RATING)
The above relations schemes are in 2NF.
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