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 Ordering  of tuples in a relation  r Relation defined as a set of tuples of elements have no order among them. Ordering of values within a tuple and an alternative definition of relation Order of attributes and values is not that important. As long as correspondence between attributes and values maintained. Alternative definition of relation Tuples considered as a set of (<attributes>, <value>) pairs. Each pairs gives the value of the mapping from an attribute A 1 to a value v 1 from dom(A 1 ). Use the first definition of relation Attributes and the values within tuples are ordered. Values and Nulls in tuple Represent the values of attributes that may be unknown or may not apply to a tuple. Meanings for null values Value Unknown Value exists but is not available Attribute does not apply to this tuple (also known as value undefined) Each value in a tuple is atomic. Flat relational model

Super Key Super Key is defined as a set of attributes within a table that uniquely identifies each record within a table. Super Key is a super-set of Candidate key. Example - Suppose we have a table that holds all the managers in a company, and that table is called Managers. The table has columns called ManagerID, Name, Title, and DepartmentID. Every manager has his/her own ManagerID, so that value is always unique in each and every row. This means that if we combine the ManagerID column value for any given row with any other column value, then we will have a unique set of values. So, for the combinations of (ManagerID, Name), (ManagerID, TItle), (ManagerID, DepartmentID), (ManagerID, Name, DepartmentID), etc – there will be no two rows in the table that share the exact same combination of values, because the ManagerID will always be unique and different for each row. This means that pairing the Manager ID with any other column(s) will ensure that the

Domain Domain denoted by D. Every attribute has some pre-defined value scope, known as attribute domain. Domain D is a set of atomic values (indivisible).Data type or format is to be specified for each domain. Ex. Name: set of characters strings that represent names of person. Employee_ages: Possible age of employees must be integer values between 15 to 80. Academic_department_codes: values must be ‘CS’, ’ECON’, ‘PHYS’. Attribute   In a relation table, each column is called by its column name or attribute name . the name of a role played by a domain in that relation Exa- s-name, s-id, s-add etc. Tuple   A single row of a table, which contains a single record for that relation is called a tuple. Relation A Database structured to recognize relation between stored items as information. Relation schema   Relation Schema denoted by R. A relation schema describes the relation name(table name),

For a small personal database, one person defines, constructs and manipulates the database . For a large organization, many people are involved in the design, use and maintenance of the large database Two types of actors of DBMS: 1. Actors on the Scene (day-to-day use of large database ) 2. Workers behind the Scene ( work to maintain database environment and are not involved in its contents ) Actors on the Scene Database administrators (DBA) are responsible for:  Authorizing access to the database  Coordinating and monitoring its use  Acquiring software and hardware resources Database designers are responsible for:  Identifying the data to be stored  Choosing appropriate structures to represent and store this data . End users - People whose jobs require access to the database.  Types of End Users • Casual end users • Naive or p

Advantages of D ata b ase As database is required in every field, so it has many advantages, Few of these advantages are as. Minimal Redundancy Privacy and Security Easy Searching Integrity Consistency Simplicity Full Control Data Migration Sharing Of Data In DBMS, Data can be shared in between authorized user of database. All the users have their own right to access the database up to a level. Database Administration has complete access of database. He can assign users to access the database. Others users are also authorized to access database and also they can share data between them. Many users have same authority to access the database. Data Consistency DBMS controls data redundancy which in turn controls data consistency. Data consistency means if you want to update data in any files then all the files should not be updated again. As in DBMS, data is stored in a single database so data becomes more

D ata :  A data is a piece of information or facts. A data can be in any form like numbers, texts, piece of paper, measurements and bytes . For example , Student name, age, class, roll no. image etc. A file, pdf and document can also be a data. A database is an organized collection of data . It is the collection of schemas , tables , queries , reports, views , and other objects. OR Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information. K ey features of DATABASE . Database is always well ordered. Database is interlinked. It is stored only once. Easy retrieval of information Made up of fields, records and files For exampl e a phone book carrying thousand of numbers in it is the basic example of database. In phone book you can search any number without any problem because all the numbers are arranged in a systemic order. Other Examples are: Electric Serv