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Three-Schema Architecture & Data Independence | Neso Academy | YouTubeToText
YouTube Transcript: Three-Schema Architecture & Data Independence
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Video Transcript
[Music]
hello everyone and welcome back
in this video we are going to look into
the database system architecture
in our initial videos we have seen the characteristics
characteristics
of database approach so here we are
going to learn about an architecture for
database systems
called the three schema architecture
that helps achieve the characteristics
of database approach that we have
already discussed earlier and with the help
help
of three schema architecture we will
also learn the concept of data independence
independence
this is a three schema architecture the
goal of this three schema
architecture is to separate the user
applications and physical database
the user application is at the topmost
level of the database system
and the physical database is at the
lowest level
here schemas can be defined at three levels
levels
the first level is the internal level this
this
internal level has an internal schema
and this schema
describes the physical storage structure
of the database
and this internal schema uses one of the
category of data models that is the low level
level
or the physical data models which we
discussed in the previous video
it uses that physical data model to describe
describe
complete details of how data is stored
and the access paths for the database
we have also seen what an access path is
in our previous video
so this is one of the levels of the
three schema architecture the internal level
level
the next level in our three schema
architecture is the conceptual level
the conceptual level has a conceptual schema
schema
and this schema describes the structure
of the database
this schema hides the details of the
physical storage structure of the
database and it concentrates or focuses
more on describing entities data types
relationships constraints attributes
etc again we have already seen the
definition of all these terminologies in
our earlier videos
and these terminologies will be useful further
further
so that is about the conceptual level
the top most level that we have in our
three schema architecture is the
external level
the external level has a number of
external schemas or external views
and each external schema describes the
part of the database that a user
is interested in and hides the rest of
the database from the user group
that is an external schema or view
contains only that data which a user
group is interested in and hides the
remaining database from that particular
user group
so this level has a view for each user group
group
so this is about the three levels and
because it has three levels it is called as
as
three schema architecture here in the
three schema
architecture each user refers to its own
external schema
so any request specified in the external
schema is sent to the conceptual schema
by the dbms and further that request is
sent to the internal schema for processing
processing
if the request from the user is a
retrieval of data from the database
then data is extracted from the stored database
database
this process of transforming requests
and results
between these three levels is called as mapping
mapping
so this is all about three schema architecture
architecture
as i said with this concept of three
schema architecture
we can further explain the concept of data
data
independence first let us see the
definition of data independence
data independence can be defined as the capacity
capacity
to change the schema at one level of a
database system
without having to change the schema at
the next
higher level that is without data independence
independence
if we make any changes at the internal
level or to the internal schema
then we have to change the higher levels
too but
with data independence when we change
the schema at one level
it doesn't affect the schema at higher levels
levels
schemas don't change frequently but if
required to change
with this concept of data independence
any changes made to the schemas will not
affect the higher levels hope you
understood the definition of data independence
independence
now let's look into the types of data
independence the first type of data
independence is the logical data independence
independence
logical data independence works between
the conceptual schema
and the external schema now what is
logical data
independence it is the ability or the
capacity to
modify the conceptual schema without
having to change
the external schemas or the application
programs for example if i want to add a
new data item
or a new attribute then that
modification of the conceptual schema
will not affect the external schema
because of
logical data independence we can alter
the table in any way in this schema
without having to change the external
schema or the application programs that refer
refer
this conceptual schema so this is about
the first
type of data independence the logical
data independence
the next type of data independence is
the physical data independence
this type of data independence works
between the
internal schema and the conceptual schema
schema
physical data independence is defined as the
the
ability or the capacity to modify the
internal schema
without having to change the conceptual schema
schema
changes to the internal schema could be
like changing the file location
the access paths etc but this does not
alter or change the conceptual schema as
long as the same data is stored or
present in the database
and this modification or changes are
required or may be needed to
improve performance like for example
changes to the access path might be
required to improve the retrieval speed
of a particular record
and this is about the second type of
data independence the physical data independence
independence
that's all about data independence and
this data independence occurs when we
have to change the schema
at one level without affecting the
schema at the next
higher level only the mapping between
the two levels
is changed with this we come to the end
of this video
hope you understood the concept of three
schema architecture
and also the concept of data
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