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Architecture of DBMS
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Introduction : DBMS Architecture
• DBMS is a collection of programs that enable the users to create and
maintain the database .
• Purpose of DBMS is to provide the user with the abstract view of
database i.e. system does not provide all the details of the data, rather it
hides the details how data is stored & maintained.
• In order to use the system, data must be retrieved efficiently.
• This leads to the design of complex data structures in the database.
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DBMS Architecture
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Three levels of the architecture
 External – individual user view
 Conceptual – community user view
 Internal – physical or storage view
The three level database architecture allows a clear
separation of the information meaning (conceptual
view) from the external data representation and from
the physical data structure layout. A database system
that is able to separate the three different views of data
is likely to be flexible and adaptable. This flexibility and
adaptability is data independence

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External View/ Level / Schema/ User View/Global View
• Highest or Top level of data abstraction ( No knowledge
of DBMS S/W and H/W or physical storage).
• This level is concerned with the user.
• Each external schema describes the part of the
database that a particular user is interested in and
hides the rest of the database from user.
• There can be n number of external views for database
where n is the number of users.
• For example, a accounts department may only be
interested in the student fee details. It would not be
expected to have any interest in the personal
information about students.
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Conceptual View
• This level is in between the user level and physical storage
view.
• There is only one conceptual view for single database.
• It hides the details of physical storage structures and
concentrates on describing entities, data types, relationships,
user operations, and constraints.
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Internal View / Physical View
• It is the lowest level of data abstraction. (it has the
knowledge about s/w and h/w)
• At this level, it keeps the information about the actual
representation of the entire database i.e. the actual storage
of the data on the disk in the form of records or blocks.
• It is close to the physical storage method.
• The internal view is the view that tells us what data is stored
in the database and how. At least the following aspects are
considered at this level: Storage allocation, Access paths etc.
• The internal view does not deal with the physical devices
directly. Instead it views a physical device as a collection of
physical pages and allocates space in terms of logical pages.
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TYPES OF DATA INDEPENDENCE
1. LOGICAL DATA INDEPENDENCE
2. PHYSICAL DATA INDEPENDENCE
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LOGICAL DATA INDEPENDENCE
• Whenever, there is a change or modification at the
conceptual level without affecting the user level or
external level, it is known as logical data independence.
• E.g. The name field in conceptual view is stored as first
name, middle name and last name whereas in external
view, it remains to be as a single name field.
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PHYSICAL DATA INDEPENDENCE
• Whenever, the changes are made at the internal level
without affecting the above layers, it is known as physical
data independence.
• E.g. The location of the database, if changed from C drive
to D drive will not affect the conceptual view or external
view as the commands are independent of the location of
the database.
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Difference between Logical Data Independence & Physical Data
Independence
Application program need not be changed if
new fields are added or deleted from the
database.
Logical Data Independence Physical Data Independence
It is concerned with the structure of the data or It is concerned with storage of
the data.
changing the data definition.
It is very difficult as the retrieving of data are It is easy to retrieve.
heavily dependent on logical structure of data. Physical database is concerned with the
change of the storage device.
It is concerned with the conceptual schema. It is concerned with the internal sche
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Database Languages and Interfaces
• DDL
• DML
• DCL
• TCL
A database management system (DBMS) interface is a user interface which
allows for the ability to input queries to a database without using the query
language itself.
1. Menu-Based Interfaces for Web Clients or Browsing
These interfaces present the user with lists of options (called menus) that
lead the user through the formation of a request. Basic advantage of using
menus is that they removes the tension of remembering specific
commands and syntax of any query language, rather than query is
basically composed step by step by collecting or picking options from a
menu that is basically shown by the system. Pull-down menus are a very
popular technique in Web based interfaces.

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2. Forms-Based Interfaces
1. A forms-based interface displays a form to each user. Users can fill out
all of the form entries to insert a new data, or they can fill out only
certain entries, in which case the DBMS will redeem same type of data
for other remaining entries.
2. This type of forms are usually designed or created and programmed
for the users that have no expertise in operating system. Many DBMSs
have forms specification languages which are special languages that
help specify such forms.
3. Example: SQL* Forms is a form-based language that specifies queries
using a form designed in conjunction with the relational database
schema

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3. Graphical User Interface
A GUI typically displays a schema to the user in diagrammatic form.
The user then can specify a query by manipulating the diagram. In
many cases, GUI’s utilize both menus and forms. Most GUIs use a
pointing device such as mouse, to pick certain part of the displayed
schema diagram.
4. Interfaces for DBA
Most database system contains privileged commands that can be
used only by the DBA’s staff. These include commands for creating
accounts, setting system parameters, granting account authorization,
changing a schema, reorganizing the storage structures of a
databases

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• Data Definition Language (DDL) statements are used to define
the database structure or schema.
Commands:
1) CREATE - to create objects in the database
2) ALTER - alters the structure of the database
3) DROP - delete objects from the database
4) TRUNCATE - remove all records from a table, including all
spaces allocated for the records are removed
5) RENAME - rename an object

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• Data Manipulation Language (DML) statements are used for
managing data within schema objects.
Commands:
1) SELECT - retrieve data from the a database
2) INSERT - insert data into a table
3) UPDATE - updates existing data within a table
4) DELETE - deletes all records from a table, the space for the
records remain
5) MERGE - UPSERT operation (insert or update)

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• Data Control Language (DCL) statements.
Commands:
1) GRANT - gives user's access privileges to database
2) REVOKE - withdraw access privileges given with the
GRANT command

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• Transaction Control (TCL) statements are used to manage the
changes made by DML statements. It allows statements to be
grouped together into logical transactions.
Commands:
1) COMMIT - save work done
2) SAVEPOINT - identify a point in a transaction to which you can later
roll back
3) ROLLBACK - restore database to original since the last COMMIT

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Classification of Database Management Systems
 Data model
•Relational
•Object
•Hierarchical and network (legacy)
 Number of users
•Single-user
•Multiuser
Number of sites
•Centralized
•Distributed
•Homogeneous
•Heterogeneous
Cost
•Open source
•Different types of licensing

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Types of access path options
General or special-purpose
Note : DBMS classification criteria:
Data model, number of users, number of sites, access paths and cost