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UNIT I:
INTRODUCTION
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UNIT 1: Introduction
Data Vs Information Database Management System(DBMS)
Database System Applications Purpose of Database Systems View of Data
Data-Models
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DATA
Vs
INFORMATION
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Database Management System (DBMS)
DBMS contains information about a particular
enterprise
Collection of interrelated data Set of programs to access the data
An environment that is both convenient
and efficientto use
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Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Online retailers: order tracking, customizedrecommendations
Manufacturing: production, inventory, orders, supplychain
Human resources: employee records, salaries, taxdeductions
Databases touch all aspects of our lives
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Purpose of Database Systems
In the early days, database applications were built directly on top of file
systems
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in differentfiles
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation multiple files and formats
Integrity problems Integrity constraints (e.g. account balance > 0) become
buried in program code rather than being stated explicitly
Hard to add new constraints or change existing ones
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Purpose of Database Systems (Cont.)
Drawbacks of using file systems (cont.)
Atomicity of updates
Failures may leave database in an inconsistent state with partialupdates carried out
Example: Transfer of funds from one account to another should eithercomplete or not happen at all
Concurrent access by multiple users
Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
Example: Two people reading a balance and updating it at the
same time Security problems
Hard to provide user access to some, but not all, data
Database systems offer solutions to all the above problems
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Levels of Abstraction
Physical level: describes how a record (e.g., customer) is stored.
Logical level: describes data stored in database, and the
relationships among the data.
type customer=record
customer_id: string;
customer_name : string;
customer_street: string;
customer_city: string;
end;
View level: application programs hide details ofdata types.
Views can also hide information (such as an employees salary)
for security purposes.
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View of DataAn architecture for a database system
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Instances and Schemas Schema the logical structure of the database
Example: The database consists of information about a set of customers
and accounts and the relationship between them)
Analogous to type information of a variable in a program
Physical schema: database design at the physical level
Logical schema: database design at the logical level
Instance the actual content of the database at a particular point in time
Analogous to the value of a variable
Physical Data Independence the ability to modify the physical schema
without changing the logical schema
Applications depend on the logical schema
In general, the interfaces between the various levels and components
should be well defined so that changes in some parts do not seriously
influence others.
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Data Models
A collection of tools for describing
Data
Data relationships
Data semantics
Data constraints
Relational model
Entity-Relationship data model (mainly for database design)
Object-based data models (Object-oriented and Object-relational)
Semi-structured data model (XML) Other older models:
Network model Hierarchical model
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Data Manipulation Language (DML)
Language for accessing and manipulating the data organized by the appropriate
data model
DML also known as query language
Two classes of languages
Procedural user specifies what data is required and how to get those data Declarative (nonprocedural) user specifies what data is required without
specifying how to get those data
SQL is the most widely used query language
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Data Definition Language (DDL)
Specification notation for defining the database schema
Example: create table account(account_number char(10),
branch_name char(10),
balance integer)
DDL compiler generates a set of tables stored in a data dictionary
Datad
ictionary contains metad
ata (i.e.,d
ata aboutd
ata) Database schema
Data storage and definition language
Specifies the storage structure and access methods used
Integrity constraints
Domain constraints
Referential integrity (e.g. branch_name must correspond to a validbranch in the branch table)
Authorization
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Database Application Architectures
(web browser)
Old Modern
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Database Users
Users are differentiated by the way they expect to interact with
the system
Nave users invoke one of the permanent application programs that have been
written previously Examples, people accessing database over the web, bank tellers, clerical staff
Application programmers interact with system through DML calls
Sophisticated users form requests in a database query language
Specialized users write specializeddatabase applications that do not fit into the
traditional data processing framework
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Database Administrator
Coordinates all the activities of the database system
has a good understanding of the enterprises information resources and
needs.
Database administrator's duties include:
Storage structure and access methoddefinition
Schema and physical organization modification
Granting users authority to access the database
Backing up data
Monitoring performance and responding to changes
Database tuning
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The Entity-Relationship Model
Models an enterprise as a collection ofentities andrelationships
Entity: a thing or object in the enterprise that is distinguishable from
other objects
Described by a set ofattributes
Relationship: an association among several entities Representeddiagrammatically by an entity-relationship diagram:
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Entity-Relationship (E-R)
The entity-relationship data model
perceives the real world that consistsof a set of basic objects entities and
a relationships among the objects.
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Entity and Entity set
An entity is an object that exists in
the real world and is distinguishable
from other objects.
The collection of all entities of the
same type is an entity set.
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NOTATION FOR ER DIAGRAM
Meaning
ENTITY TYPE
WEAK ENTITY TYPE
RELATIONSHIP TYPE
IDENTIFYING RELATIONSHIP TYPE
ATTRIBUTE
KEY ATTRIBUTE
MULTIVALUED ATTRIBUTE
COMPOSITE ATTRIBUTE
DERIVED ATTRIBUTE
TOTAL PARTICIPATION OF E2 IN R
CARDINALITY RATIO 1:N FOR E1:E2 IN R
STRUCTURAL CONSTRAINT (min, max) ON PARTICIPATION OF E IN R
Symbol
E1 R E2
E1 R E2
R(min,max)
E
N
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The Entity-Relationship Model
Models an enterprise as a collection ofentities andrelationships
Entity: a thing or object in the enterprise that is distinguishable from
other objects
Described by a set ofattributes
Relationship:an association among several entities
Representeddiagrammatically by an entity-relationship diagram:
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FIGURE :An ER diagram for a BANK database schema.
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Do it yourself..
Question:
Construct a ER diagram to show a depositor
relationship that associates a customer witheach account that he has.
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Slide 3-24
An ER schema diagram for the COMPANY database.
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Slide 3-25
FIGURE : An ER diagram for an AIRLINE database schema