Dbms unit01

DATABASE MANAGEMENT SYSTEMS
B. Tech II/CSE II Semester
UNIT-I PPT SLIDES
Text Books: (1) DBMS by Raghu Ramakrishnan
(2) DBMS by Sudarshan and Korth
1

 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
2

 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.
3

 Data independence and efficient access.
 Reduced application development time.
 Data integrity and security.
 Uniform data administration.
 Concurrent access, recovery from crashes.
4

 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
5
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 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
6

 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
7

 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
8

 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.
9

 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.
10

11
An architecture for a database system

 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
12

 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.
13

 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
14

 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.
15

 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)
16

 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.
17
One of the most important benefits of using a DBMS!

 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
18

 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
19

 Example of tabular data in the relational model
20
Attributes

 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
22

 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
23

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
24

 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
25

 Storage management
 Query processing
 Transaction processing
26

 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
27

1.Parsing and translation
2. Optimization
3. Evaluation
28

 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
29

 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.
30

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
31

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