19-01-2006

Dependencies of three types
Partial Dependencies.
Transitive.
Functional

Functional Dependency is set to exist when Non Primary key is dependent on Primary key and also on the whole of primary key.

For successful operation of RDBMS, normalized tables are required.

Normalization is a process of identifying primary key and ensuring that all the non key attributes (all the columns in a table not a part of primary key) have full functional dependencies on the primary key and whole of the primary key.

RDBMS can handle one to many relationships.

Normalization can also be defined as resolving many to many relationships to one to many relationships.

Degree of normalized data is measured in normal form.

Oracle claims that it has implemented 11.5 rules of E.F. Codd. But few critics say that it is a false claim because according to them Oracle has implemented only 8 rules. What ever may be the controversy but fact remains that Oracle has implemented maximum rules proposed by E.F. Codd.

Primary and Foreign Keys values are Functional values.

Non Program Access or Non Procedural Access (E. F. Codd)
In this method of accessing data user may not be required to know the programming to access the data. It doesn’t mean that no procedure is followed to access the data. Of course some procedure is followed but user doesn’t need to worry about it. Following the procedure is part and parcel of Database. In brief it is Database’s responsibility and not user’s. All user needs to do is to select the data he needs.

For Non Procedural access we need to know different Languages. E.F. Codd proposed the language SQL. SQL stands for Structured Query Language.

Different statements are as follows:
DML à Data Manipulation Language.
EG: Insert, Update, Delete,

DLL à Create, Drop


DCL à Data Control Language

TC à Transaction.
EG: Rollback

Administration.
EG: Startup, Shutdown and Archive.


Oracle also provides procedural method called PL/SQL. PL/SQL stands for Programmable Language Structured Query Language.

Next feature of RDBMS is Relational Algebra.

Set of attributes is called Table. Tables are defined only by columns. Rows came after columns. You don’t need columns to define Table.

Set algebra related to relational sets is called Relational Algebra.

Selection
Projection
Intersection
Mining
Union
Product
Join

Selection: Selection allows you to provide certain Laws. Selection is a process of filtering.

Projection: If I want to select a particular attribute or I want to select whole set of attributes or columns then the procedure of selection is called Projection.

Intersection: If there are two sets A and B and I want to select the elements common to set A and set B, then the procedure of selection of such elements is called Intersection.
Take for instance A= {1, 3, 5, 6, 9} and B= {3, 4, 5, 8}
Then A intersection B = {3, 5}

Union: Again considering above example if I want to select the elements such that the new set includes all the elements of A and B but excluding the repeated elements then such a method of selection of elements is called Union. Therefore A union B = {1, 3, 4, 5, 6, 8, 9}

We can also take union in such a manner that A union B includes the elements which are repeated as well.

Product: A = {1, 3, 5} and B = {2, 4, 6}
Then A product B = {
(1, 2)
(1, 4)
(1, 6)
(3, 2)
(3, 4)
(3, 6)
(5, 2)
(5, 4)
(5, 6)
}

Scientific name of tables is called Relational.

Data Dictionary:
Tables maintained by the system or information of system stored in the form of tables is called Data Dictionary. Data Dictionary is also called Meta Data indicating that data of data. It is stored in RDBMS.

Concept of Null:
If certain value is not known or not applicable then it is called Null. Null is not equal to other null. Because either both are unknown or not applicable. Arithmetic of null is also null.
EG: null + 3 = null

Null Value Locator (NVL):
It is denoted by (x, 0) for addition and (x, 1) for multiplication. If we know the value of x then of course we will use it but if we don’t know the value of x then instead of making it null we can assign a value 0 for addition or 1 in case of multiplication.

18-01-2006

Oracle is RDBMS. RDBMS stands for Relational Data Base Management System. It was proposed by Dr. Edgar F. Codd. This database system was not widely accepted because majority of population at that time consisted of people belonging to commerce and accounts. Its obvious that all applications and softwares were also made for their use. How ever RDBMS required usage of set theory which is branch of Mathematics and Arithmetics. This was not easily digestible to them. Hence it faced lot of opposition.


Update Anomaly. (If we have to update particular entity and in case that entity is present at no of places then there are chances that we may forget to change that entity at some place. )

Deletion Anomaly. ( If we delete some data the other data should remain intact. Take for example that if particular student has completed his course and hence leaving the institute then his account needs to be get deleted. But in that case other entities like Subject detail, Fees detail, Duration and phone no etc will also get deleted.)

Insertion Anomaly. (Using this method of storing data we can store data for only the items which we have presently in our hand. Suppose a new course is started then it is not possible to make its entry.)


Transitive Dependencies:
When non primary key attributes depends on other non primary key attributes which in turn depends on some primary key attributes then it is called Transitive Dependencies.

Concept of Relational:
The meaning of the term relational is when the data is stored in the tables are related to each other through a common column as well as in each table all the attributes are related to each other by way the common functional dependencies on the primary key. The relation between the two tables typically represent the natural relation between the two entities. In the real world, entities are never isolated but they are always related to each other.