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DBMS CONCEPTS
UNIT I
INTRODUCTION
(DATABASE)
“A collection of related pieces of
data, whose purpose is to solve the
data management needs of an
institution is called
a Database.”.
INTRODUCTION
(DBMS)
“Software system that
enables users to define,
create, maintain and control
access to the database”.
DATA
VS
DATABASE
1. Storage
Besides computers,
databases can even be
maintained in physical
ledgers, books or papers.
In a database
management
system (DBMS), all
the records are
maintained only on
a computer.
2.
Data
Retrieval
The retrieval of
information from the
databases can be done
manually, through
queries or by using
programs (C, C++, Java
etc.).
We can retrieve the
data from the
database
management
system through
queries written in
SQL.
3. Speed
As databases can be
handled manually or via
computers, when SQL is
not used to retrieve
information, it can be
very slow.
As a computer
system is involved
in a database
management
system, the
retrieval of
information is very
quick.
DATA
VS
DATABASE
4. Access
The databases are not
designed for a large
number of people who can
access data at the same
time, rather it is designed
for a very small number of
people (preferably few
people) who access data at
different times.
The database
management
system is designed
for a large number
of people who can
access the data at
the same time.
5.
Data
Manipulation
In case of the databases,
very less information can
be modified at a time.
In the database
management
system (DBMS), a
lot of information
can be changed at
one time (as it can
have many users
using it at the same
time).
6.
Backup and
Recovery
The databases do not
ensure that the data will
be available after failure
arises.
The database
management
system (DBMS)
ensures that the
data will always be
Database
Management
System(DBMS)
 Collection of interrelated data
 Set of programs to access the data
 DBMS contains information about a particular
enterprise
 DBMS provides an environment that it both
convenient and efficient to use
Purposeof
Database
Systems
Database management systems were developed to handle
the following difficulties of typical file-processing systems
supported by conventional operating systems.
 Data redundancy and inconsistency
 Difficulty in accessing data
 Data isolation – multiple files and formats
 Integrity problems
 Atomicity of updates
 Concurrent access by multiple users
 Security problems
Characteristics
ofDBMS
 Real-world entity
 Relation-based tables
 Isolation of data and application
 Less redundancy
 Consistency
 Query Language
 ACID Properties (Atomicity, Consistency, Isolation,
and Durability )
 Multiuser and Concurrent Access
 Multiple views
 Security
DifferentViews
ofDatabase
 Physical Data Level
 Conceptual Data Level
 External Data Level
PhysicalData
Level
The physical schema describes details of how data is
stored: files, indices, etc. on the random access disk
system. It also typically describes the record layout of
files and type of files (hash, b-tree, flat).
ConceptualData
Level
 Also referred to as the Logical level
 Hides details of the physical level.
 In the relational model, the conceptual schema
presents data as a set of tables.
 The DBMS maps data access between the
conceptual to physical schemas automatically.
 Physical schema can be changed without
changing application:
 DBMS must change mapping from conceptual to
physical.
 Referred to as physical data independence.
ExternalData
Level
 In the relational model, the external schema also
presents data as a set of relations. An external schema
specifies a view of the data in terms of the conceptual
level. It is tailored to the needs of a particular category
of users. Portions of stored data should not be seen by
some users and begins to implement a level of security
and simplifies the view for these users
Examples:
 Students should not see faculty salaries.
 Faculty should not see billing or payment data.
Attributes,EntityandKeys
DATAMODELS
 A conceptual data model identifies the highest-level
relationships between the different entities. Features
of conceptual data model include:
 Includes the important entities and the relationships
among them.
 No attribute is specified.
 No primary key is specified.
Conceptual Data Model
Conceptual
Model
LogicalData
Model
 A logical data model describes the data in as much detail as
possible, without regard to how they will be physical implemented
in the database. Features of a logical data model include:
 Includes all entities and relationships among them.
 All attributes for each entity are specified.
 The primary key for each entity is specified.
 Foreign keys (keys identifying the relationship between different
entities) are specified.
 Normalization occurs at this level.
 The steps for designing the logical data model are as follows:
 Specify primary keys for all entities.
 Find the relationships between different entities.
 Find all attributes for each entity.
 Resolve many-to-many relationships.
 Normalization.
LogicalData
Model
PhysicalData
Model
Physical data model represents how the model will be built in the database. A
physical database model shows all table structures, including column name,
column data type, column constraints, primary key, foreign key, and
relationships between tables. Features of a physical data model include:
 Specification all tables and columns.
 Foreign keys are used to identify relationships between tables.
 Denormalization may occur based on user requirements.
 Physical considerations may cause the physical data model to be quite
different from the logical data model.
 Physical data model will be different for different RDBMS. For example,
data type for a column may be different between MySQL and SQL Server.
 The steps for physical data model design are as follows:
 Convert entities into tables.
 Convert relationships into foreign keys.
 Convert attributes into columns.
 Modify the physical data model based on physical constraints / requirements
PhysicalData
Model
Database
Schema
 A database schema is the skeleton structure that
represents the logical view of the entire database. It
defines how the data is organized and how the
relations among them are associated. It formulates all
the constraints that are to be applied on the data.
 A database schema defines its entities and the
relationship among them. It contains a descriptive
detail of the database, which can be depicted by means
of schema diagrams. It’s the database designers who
design the schema to help programmers understand
the database and make it useful.
DatabaseSchema
DatabaseSchema
Physical Database Schema − This schema pertains to the actual
storage of data and its form of storage like files, indices, etc. It
defines how the data will be stored in a secondary storage.
Logical Database Schema − This schema defines all the logical
constraints that need to be applied on the data stored. It defines
tables, views, and integrity constraints.

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Dbms unit i

  • 2. INTRODUCTION (DATABASE) “A collection of related pieces of data, whose purpose is to solve the data management needs of an institution is called a Database.”.
  • 3. INTRODUCTION (DBMS) “Software system that enables users to define, create, maintain and control access to the database”.
  • 4. DATA VS DATABASE 1. Storage Besides computers, databases can even be maintained in physical ledgers, books or papers. In a database management system (DBMS), all the records are maintained only on a computer. 2. Data Retrieval The retrieval of information from the databases can be done manually, through queries or by using programs (C, C++, Java etc.). We can retrieve the data from the database management system through queries written in SQL. 3. Speed As databases can be handled manually or via computers, when SQL is not used to retrieve information, it can be very slow. As a computer system is involved in a database management system, the retrieval of information is very quick.
  • 5. DATA VS DATABASE 4. Access The databases are not designed for a large number of people who can access data at the same time, rather it is designed for a very small number of people (preferably few people) who access data at different times. The database management system is designed for a large number of people who can access the data at the same time. 5. Data Manipulation In case of the databases, very less information can be modified at a time. In the database management system (DBMS), a lot of information can be changed at one time (as it can have many users using it at the same time). 6. Backup and Recovery The databases do not ensure that the data will be available after failure arises. The database management system (DBMS) ensures that the data will always be
  • 6. Database Management System(DBMS)  Collection of interrelated data  Set of programs to access the data  DBMS contains information about a particular enterprise  DBMS provides an environment that it both convenient and efficient to use
  • 7. Purposeof Database Systems Database management systems were developed to handle the following difficulties of typical file-processing systems supported by conventional operating systems.  Data redundancy and inconsistency  Difficulty in accessing data  Data isolation – multiple files and formats  Integrity problems  Atomicity of updates  Concurrent access by multiple users  Security problems
  • 8. Characteristics ofDBMS  Real-world entity  Relation-based tables  Isolation of data and application  Less redundancy  Consistency  Query Language  ACID Properties (Atomicity, Consistency, Isolation, and Durability )  Multiuser and Concurrent Access  Multiple views  Security
  • 9. DifferentViews ofDatabase  Physical Data Level  Conceptual Data Level  External Data Level
  • 10. PhysicalData Level The physical schema describes details of how data is stored: files, indices, etc. on the random access disk system. It also typically describes the record layout of files and type of files (hash, b-tree, flat).
  • 11. ConceptualData Level  Also referred to as the Logical level  Hides details of the physical level.  In the relational model, the conceptual schema presents data as a set of tables.  The DBMS maps data access between the conceptual to physical schemas automatically.  Physical schema can be changed without changing application:  DBMS must change mapping from conceptual to physical.  Referred to as physical data independence.
  • 12. ExternalData Level  In the relational model, the external schema also presents data as a set of relations. An external schema specifies a view of the data in terms of the conceptual level. It is tailored to the needs of a particular category of users. Portions of stored data should not be seen by some users and begins to implement a level of security and simplifies the view for these users Examples:  Students should not see faculty salaries.  Faculty should not see billing or payment data.
  • 14. DATAMODELS  A conceptual data model identifies the highest-level relationships between the different entities. Features of conceptual data model include:  Includes the important entities and the relationships among them.  No attribute is specified.  No primary key is specified. Conceptual Data Model
  • 16. LogicalData Model  A logical data model describes the data in as much detail as possible, without regard to how they will be physical implemented in the database. Features of a logical data model include:  Includes all entities and relationships among them.  All attributes for each entity are specified.  The primary key for each entity is specified.  Foreign keys (keys identifying the relationship between different entities) are specified.  Normalization occurs at this level.  The steps for designing the logical data model are as follows:  Specify primary keys for all entities.  Find the relationships between different entities.  Find all attributes for each entity.  Resolve many-to-many relationships.  Normalization.
  • 18. PhysicalData Model Physical data model represents how the model will be built in the database. A physical database model shows all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables. Features of a physical data model include:  Specification all tables and columns.  Foreign keys are used to identify relationships between tables.  Denormalization may occur based on user requirements.  Physical considerations may cause the physical data model to be quite different from the logical data model.  Physical data model will be different for different RDBMS. For example, data type for a column may be different between MySQL and SQL Server.  The steps for physical data model design are as follows:  Convert entities into tables.  Convert relationships into foreign keys.  Convert attributes into columns.  Modify the physical data model based on physical constraints / requirements
  • 20. Database Schema  A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied on the data.  A database schema defines its entities and the relationship among them. It contains a descriptive detail of the database, which can be depicted by means of schema diagrams. It’s the database designers who design the schema to help programmers understand the database and make it useful.
  • 22. DatabaseSchema Physical Database Schema − This schema pertains to the actual storage of data and its form of storage like files, indices, etc. It defines how the data will be stored in a secondary storage. Logical Database Schema − This schema defines all the logical constraints that need to be applied on the data stored. It defines tables, views, and integrity constraints.