Page 265 - Trackpad 402_Class-X_Final
P. 265

•  Data Value: Data Value is the value in the form of a text, number, date, audio, video, picture, etc. It is the smallest unit
              of a database and is formed by the intersection of a row and a column. Vertically it is a part of a column and makes
              a collection of similar data. Horizontally it is a part of a row and represents one complete information of a student
            Let us take the example of student table as shown below:

                                                           Student



                         Rollno       Name         Date of Birth        Address          PhoneNo
                           11     Amaira            12/04/2007     Rohini                11223344
                           21     Shubham           01/03/2007     Kailash Colony        23234455
               Table       12     Smith             21/09/2006     Pitampura             34344455
                                                                                                           Records
                           33     Tisha             15/08/2006     Rohini                66778899
                           17     Smith             20/05/2007     Defence Colony        11227788
                           35     Tvesha            12/04/2007     Greater Kailash       44556677


            In the above table there are 6 rows and 5 columns. If a new student joins a school then the complete information of
            a new student will be added in the form of a record/row. The columns like Rollno will store only integers, Name will
            store only text and Date of Birth will store only Date.


                    RELATIONAL DATABASE MANAGEMENT SYSTEM (RDBMS)

            RDBMS is the next advanced form of Database Management System and is based on a Relational Model. In this model
            a relational database has a set of related tables that are interlinked to each other on the basis of a common field. It
            is a very efficient way of representing data and allows data in a table is represented in a two dimensional form and
            is known as a Relation. A row that forms complete information is known as a Tuple. Each tuple uniquely identifies a
            record on the basis of a unique key- Primary key.  Data from different relations can be easily extracted as they are
            interlinked on the basis of a Primary key. A column that stores similar data is known as an Attribute or a Key.

                                                                                                       Domain
                                                   Columns or Fields or Attributes                   5000,100000

                Primary        EMP_ID              NAME                POSTS              Salary
                  Key
                                  E1        Rahul                Clerk                    30000

               Rows               E2        Kapil                Manager                  90000
              Records                                                                                      Cardinality    (No. of Rows) = 4
             or Tuples            E3        Manoj                Clerk                    90000

                                  E4        Mukesh               Peon                     20000


                                                   Degree (No. of Columns) = 4                Data Value




                      The concept of relational database was developed by E.F. Codd at IBM in 1970.






                                                                                   Database  Management System  265
   260   261   262   263   264   265   266   267   268   269   270