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DATABASE MANAGEMENT SYSTEM
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DATABASE, • A Database is a collection of interrelated data., • It is used to serve multiple application concurrently.
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DATABASE SYSTEM, • It is a Computer based Record Keeping System., • A DBMS is a software responsible for storing, maintaining and, utilizing databases., , • A database system is a repository of the data needed for an, organization’s data processing.
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RELATIONAL DATABASE MODEL, • Simplest model among all models (Network, Hierarchical & Relational), • Data is organized into Relation (Database), • Database is an organized set of interrelated data organized into rows and, columns., , • Rows are known as Tuple. These are the horizontal sub-set of the relation., • Columns are known as Attributes. These are the vertical sub-set of the relation.
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SOME TERMINOLOGY, • Entity, • It is a set of organized tuples (records)., , • Domain, • Group of all possible values that an attribute may hold., , • Cardinality, • Total Number of tuples / records in, , an entity (relational), , • Degree, • Total Number of attributes / columns in an entity (relation)
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KEYS, • Key is used to identify records in a relation / entity., • Types:, • Primary Key, • Candidate Key, • Alternate Key, • Foreign Key
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KEYS: PRIMARY KEY, • Primary key is an attribute or group of attributes used to identify, records / tuples in a relation uniquely., , • It should not be NULL, • It must be unique., e.g. Student relation may has any one Primary key from the followings:, RollNo, Name, RollNo+Marks, RollNo+Name
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KEYS: CANDIDATE KEY, • A key which can be served an a Primary key in a relation., e.g. Student relation may have following Candidates Keys:, , RollNo, Name, RollNo+Marks, RollNo+Name
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KEYS: ALTERNATE KEY, • A key which may be used as a Primary key in a relation among all, Candidate keys., e.g. Student relation may have following Candidates Keys:, RollNo, Name, RollNo+Marks, RollNo+Name, Let RollNo is selected as a Primary Key, then all other keys are, Alternate keys.
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KEYS: FOREIGN KEY, • A non-key attribute of a relation whose values are derived from, primary key of another relation is known as foreign key in its, current relation., Marks, , Student, RollNo, , Name, , RollNo, , PT1, , PT2, , 1101, , Ram, , 1101, , 12, , 18, , 1102, , Gopi, , 1102, , 15, , 19, , 1103, , Krishna, , 1103, , 13, , 18, , 1104, , Yuvraj
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RECAPSULATION, • Relation, • Tuple, Attribute, • Cardinality, Degree, • Keys: Primary, Candidate, Alternate, Foreign
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ASSIGNMENTS, • Write difference between Primary key and Foreign Key?, • Define:, •, •, •, •, , Candidate Key, Alternate Key, Cardinality, Degree, , • Name some attributes in a relation LIBRARY used to store books.
