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[Music]
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hello friends welcome back to our
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channel
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so in today's session we'll discuss
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about one more topic in
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dbms that is
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schema
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and
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instance
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so what is the schema and what is the
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instance
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so coming to the schema
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the schema in a database
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is treated as a
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structure
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of
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any database
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is represented as a schema
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okay so not the data it's a structure
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so consider some student table
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consider the student table so student
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can be identified
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by using role number
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name
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some college
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etc
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so
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this is called
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structure
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and here we call it as a
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schema
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so schema is a structure which the
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database follows is known as schema
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now
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this schema is divided into three
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categories okay and this database design
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will be done in three types three levels
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so
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the first level
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physical level
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and the second one
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logical level
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level three
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view level
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right so here the schema that means the
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design of a database can be done in
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three different levels physical logical
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and view level so let me explain about
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this one and this process we call it as
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a
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three
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schema database
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okay three schema three time okay
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so
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let me explain here
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so this is the database
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physical
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logical
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okay
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so
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this is a view level
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okay
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so this is called a physical schema
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physical schema or a physical level
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and this is a logical
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schema or a logical level
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and this is a
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view schema
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and this physical schema is also known
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as the internal level
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internal
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level
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and this logical schema is also called
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as a conceptual level
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conceptual
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level
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and this view schema is also called as
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an external level
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so let us see what happens here
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so this physical schema means
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the design of a database done at the
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physical level is known as a physical
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schema
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and
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the conceptual level that means
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the database design
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done at the conceptual level is known as
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a logical schema
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and the database design
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done at the external level is known as
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view schema and here in this view schema
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there will be different views
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okay
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now
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coming to the physical
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physical schema
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here the data is stored in a physical
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storage that means how the data is
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stored
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how
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the data
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is stored
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in a storage okay in a storage
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that means in terms of files okay or
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indexes so in order to retrieve the data
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we'll use indexes so like this
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example like files
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okay files in folders
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files or folders etc etc
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that is the
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data stored in the
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database okay i mean the storage storage
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device
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and the next one is a logical schema
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logical schema
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so here
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how the data is stored in terms of
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the logical constraints okay how the
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data is actually stored that means
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in terms of tables
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so what are the constraints so
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logical constraints
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logical constraints
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right attributes
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what are the attributes
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relationship
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the relationship between
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attributes so everything will be
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designed everything will be designed in
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this particular logical level right so
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logical constraints means what is the
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primary key what is the
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foreign key everything
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right so here the implementation details
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will be hidden okay the logical schema
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the implementation details will be
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hidden but it designs the
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complete uh this
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how the data is stored in the tables
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that means how what are the attributes
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and what are the logical constraints and
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how the tables will be related one one
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with each other etcetera etc will be
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designed here
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and coming to the view schema
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coming to the view schema
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so how the user interacts with the
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database right how the user end user
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okay so this completely deals with the
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end user interaction
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with the database
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with a database
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so this will be done in the view schema
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so different users will view differently
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okay different views users will view
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differently okay
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so this is a view schema which is also
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called as an external level so that's
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why we are having a multiple views
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multiple views so based upon the user
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the view will be changed
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okay so end user interaction with the
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database so this is completely
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the schema what exactly the schema so
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let us take an example i will tell you
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the example
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so
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so if you are having a website okay so
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college website
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college website
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so here
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i am giving some role number so i am
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having one text box
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so it it will ask me about the role
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number so i need to enter the role
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number here
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and if you submit the button
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right enter this roll number some one
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zero one
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and enter the submit button so
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immediately i will get the details of a
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student in a form right
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so
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see
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roll number
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photo
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photo of the student
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name
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some branch
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cgpa
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okay
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some placement details
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placement details so i need to i'm
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getting this one okay i'm just entering
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the roll number and after clicking on
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the submit button i'm getting this page
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which consists of all the details of the
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students along with the photo photograph
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so
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this is called a view schema
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view schema so from where we are getting
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this roll number name brand cgp and
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placement details and including the
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photograph
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so here we are entering only the roll
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number
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okay here the input is only the roll
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number but we are getting the complete
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profile of a student so whatever the
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profile we are observing or which is
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visible to the user that we call it as a
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view schema so in such a way the
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database has been designed
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okay so this is called the end user
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interaction end user interaction so this
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is this is how
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okay actually the data will not be
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stored in the database in this format
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so in the database the data will be
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stored in different format but
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so coming to the user uh view we are
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getting in this way so this is called a
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view schema so actually this role number
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name branch student
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will be taken in this way so roll number
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name
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branch
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cgpa
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placement
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so
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this is a table
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this is a student table
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right
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so this is a student table and we are
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having a different records here
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we are having
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different records
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so we are having one not one one or two
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some one or three
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right so
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this is how the data is designed in the
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logical level so here the primary key is
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a roll number so which which is an
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unique identifier of the tuple okay
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which is a unique identifier of a tuple
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so roll number based upon the roll
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number we are getting all these details
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okay so this is how
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the logical schema this is how the
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logical schema is defined okay so what
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is the table what are the attributes
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these are called attributes right and
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what is a primary key what is a foreign
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key so etcetera all the logical
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constraints and how this table is
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related to another table right so
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everything will be designed in this
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logical schema
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and coming to the physical schema how
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actually these details will be stored in
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the database
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so this is the database right
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so how these details will be stored in
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the database so that means in a storage
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device in a storage device so that we
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call it as a physical scheme
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right so hope you understood this one so
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this is the schema schema is nothing but
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a structure
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of a database structure of a database
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right now
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what is an instance
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so is the instance and schema both are
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equal
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exactly it's not both are not equal so
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both are different right so instance
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means a view of a database at a
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particular moment or a particular time
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right so
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let me tell you this
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so coming to the instance
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so it is a view
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of a database
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a view of a database
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at a particular
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at a particular
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instance of time
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instance of
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time
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so
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the data data available in the database
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may change frequently right so
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for example
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today we are having
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some
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50 student records
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right so records of 50 students
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so maybe
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tomorrow
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let it be a few more students have been
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added right let it be some 75 students
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have been added
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so
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at that particular moment so this is a
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view of a database
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so an instance means
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which i mean the data of a database can
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be changed frequently that means the
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instance will be changed from time to
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time
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but the schema is a structure which will
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be
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fixed and
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we have to follow the schema so that
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structure of a database
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so we can't change the schema frequently
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right so that is a major difference
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between the schema and instance
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so schema can be categorized into three
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levels so
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internal level conceptual level and the
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external level internal level means
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database design
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at the physical physical level and
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conceptual level means the database
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design at the logical level and the
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external level the database design it
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end user interaction that means a view
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level
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okay so it will be having the multiple
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views so this is about the difference
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between the schema and instance so hope
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you understood this difference so if you
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are having any doubts regarding this
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instance and schema feel free to post
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your dots in the comment section
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definitely i will try to clarify all
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your doubts if you really enjoyed my
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