Unit01 dbms 2

DATABASE MANAGEMENT SYSTEMS

TERM 2008-09

B. Tech II/IT II Semester

UNIT-I PPT SLIDES

Text Books: (1) DBMS by Raghu Ramakrishnan
(2) DBMS by Sudarshan and Korth

Slide No:L3-5

INDEX
UNIT-1 PPT SLIDES
S.NO Module as per Lecture PPT
Session planner No Slide NO
------------------------------------------------------------------------------------------
6. DBS Application and L1 L1- 1 to L1- 9
DBMS Vs File Systems
2. View of DATA L2 L2- 1 to L2- 7
3. DB Language (DML, DDL) L3 L3- 1 to L3- 6
4. DB Users and Administrator L4 L4- 1 to L4- 3
5. Data storage and Querying L5 L5- 1 to L5 -5
6. DBMS Architecture L6 L6- 1 to L6- 3

Slide No:L3-5

Database System Applications
• 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 efficient to use
• Database Applications:
– Banking: all transactions
– Airlines: reservations, schedules
– Universities: registration, grades
– Sales: customers, products, purchases
– Online retailers: order tracking, customized recommendations
– Manufacturing: production, inventory, orders, supply chain
– Human resources: employee records, salaries, tax
deductions
• Databases touch all aspects of our lives

Slide No:L1-1

What Is a DBMS?

• A very large, integrated collection of data.
• Models real-world enterprise.
– Entities (e.g., students, courses)
– Relationships (e.g., Madonna is taking
CS564)
• A Database Management System (DBMS) is a
software package designed to store and
manage databases.

Slide No:L1-2

Why Use a DBMS?

• Data independence and efficient
access.
• Reduced application development
time.
• Data integrity and security.
• Uniform data administration.
• Concurrent access, recovery from
crashes.

Slide No:L1-3

Why Study Databases?? ?

• Shift from computation to information
– at the “low end”: scramble to webspace (a mess!)
– at the “high end”: scientific applications

• Datasets increasing in diversity and volume.
– Digital libraries, interactive video, Human
Genome project, EOS project
– ... need for DBMS exploding

• DBMS encompasses most of CS
– OS, languages, theory, AI, multimedia, logic

Slide No:L1-4

Files vs. DBMS

• Application must stage large datasets
between main memory and secondary
storage (e.g., buffering, page-oriented
access, 32-bit addressing, etc.)
• Special code for different queries
• Must protect data from inconsistency
due to multiple concurrent users
• Crash recovery
• Security and access control

Slide No:L1-5

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
different files
– 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
Slide No:L1-6

Purpose of Database Systems (Cont.)

• Drawbacks of using file systems (cont.)
– Atomicity of updates
• Failures may leave database in an inconsistent state
with partial updates carried out
• Example: Transfer of funds from one account to
another should either complete 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

Slide No:L1-7

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 of data
types. Views can also hide information (such as an
employee’s salary) for security purposes.

Slide No:L1-8

Summary
• DBMS used to maintain, query large datasets.
• Benefits include recovery from system crashes,
concurrent access, quick application development,
data integrity and security.
• Levels of abstraction give data independence.
• A DBMS typically has a layered architecture.
• DBAs hold responsible jobs
and are well-paid! 
• DBMS R&D is one of the broadest,
most exciting areas in CS.

Slide No:L1-9

View of Data

An architecture for a database system

Slide No:L2-1

Instances and Schemas

• Similar to types and variables in programming
languages
• 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
Slide No:L2-2

Instances and Schemas
• 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.

Slide No:L2-3

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

Slide No:L2-4

Data Models

• A data model is a collection of concepts for
describing data.
• A schema is a description of a particular
collection of data, using the a given data
model.
• The relational model of data is the most
widely used model today.
– Main concept: relation, basically a table with
rows and columns.
– Every relation has a schema, which describes
the columns, or fields.

Slide No:L2-5

Example: University Database
• Conceptual schema:
– Students(sid: string, name: string, login:
string,
age: integer, gpa:real)
– Courses(cid: string, cname:string,
credits:integer)
– Enrolled(sid:string, cid:string, grade:string)

• Physical schema:
– Relations stored as unordered files.
– Index on first column of Students.

• External Schema (View):
– Course_info(cid:string,enrollment:integer)
Slide No:L2-6

Data Independence
• Applications insulated from how data
is structured and stored.
• Logical data independence: Protection
from changes in logical structure of
data.
• Physical data independence:
Protection from changes in physical
structure of data.
One of the most important benefits of using a DBMS!
Slide No:L2-7

DATA BASE LANGUAGE
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

Slide No:L3-1

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
• Data dictionary contains metadata (i.e., data about data)
– 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 valid branch in the branch table)
– Authorization

Slide No:L3-2

Relational Model

• Example of tabular data in the Attributes

relational model

Slide No:L3-3

A Sample Relational Database

Slide No:L3-4

SQL
• SQL: widely used non-procedural language
– Example: Find the name of the customer with
customer-id 192-83-7465
select customer.customer_name
from customer
where customer.customer_id = ‘192-83-7465’
– Example: Find the balances of all accounts held by
the customer with customer-id 192-83-7465
select account.balance
from depositor, account
where depositor.customer_id = ‘192-83-7465’
and
depositor.account_number =
account.account_number

Slide No:L3-5

SQL

• Application programs generally access databases
through one of
– Language extensions to allow embedded SQL
– Application program interface (e.g., ODBC/JDBC)
which allow SQL queries to be sent to a database

Slide No:L3-6

Database Users

Users are differentiated by the way they expect to interact with
the system
• Application programmers – interact with system through
DML calls
• Sophisticated users – form requests in a database query
language
• Specialized users – write specialized database applications
that do not fit into the traditional data processing framework
• Naïve users – invoke one of the permanent application
programs that have been written previously
– Examples, people accessing database over the web, bank
tellers, clerical staff

Slide No:L4-1

Database Administrator

• Coordinates all the activities of the database system
– has a good understanding of the enterprise’s
information resources and needs.
• Database administrator's duties include:
– Storage structure and access method definition
– Schema and physical organization modification
– Granting users authority to access the database
– Backing up data
– Monitoring performance and responding to
changes
• Database tuning

Slide No:L4-2

Data storage and Querying

• Storage management
• Query processing
• Transaction processing

Slide No:L5-1

Storage Management

• Storage manager is a program module that provides
the interface between the low-level data stored in the
database and the application programs and queries
submitted to the system.
• The storage manager is responsible to the following
tasks:
– Interaction with the file manager
– Efficient storing, retrieving and updating of data
• Issues:
– Storage access
– File organization
– Indexing and hashing

Slide No:L5-2

Query Processing

1.Parsing and translation
2. Optimization
3. Evaluation

Slide No:L5-3

Query Processing (Cont.)

• Alternative ways of evaluating a given query
– Equivalent expressions
– Different algorithms for each operation
• Cost difference between a good and a bad way of
evaluating a query can be enormous
• Need to estimate the cost of operations
– Depends critically on statistical information about
relations which the database must maintain
– Need to estimate statistics for intermediate
results to compute cost of complex expressions

Slide No:L5-4

Transaction Management

• A transaction is a collection of operations that
performs a single logical function in a database
application
• Transaction-management component
ensures that the database remains in a
consistent (correct) state despite system
failures (e.g., power failures and operating
system crashes) and transaction failures.
• Concurrency-control manager controls the
interaction among the concurrent transactions,
to ensure the consistency of the database.

Slide No:L5-5

Database Architecture

The architecture of a database systems is greatly
influenced by
the underlying computer system on which the
database is running:
• Centralized
• Client-server
• Parallel (multiple processors and disks)
• Distributed

Slide No:L6-1

Overall System Structure

Slide No:L6-2

Database Application Architectures

(web browser)

Old Modern

Slide No:L6-3

Unit01 dbms 2

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