database management unit-i
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UNIT
I
Introduction to Database Systems
DATABASE MANAGEMENT SYSTEMS
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Terminology
Data = known facts that can be recorded
Database (DB) = logically coherent collection of related data with some inherent
meaning
Entities such as students, courses, sections
Relationships between entities such as students taking courses and sections
being part of courses
Database management system (DBMS) = collection of programs that enable
users to create and maintain a DB; general-purpose software system that
facilitates process of defining, constructing, and manipulatingDBs for various
applications.
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A shared collection of logically related data and a description of this
data, designed to meet the information needs of an organization
Data repository (data resource)
Designed independently of applications (i.e., data abstraction)
Long-term information needs at the enterprise level
Primarily designed for quick and efficient data retrieval
What is database?
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What the Purpose for Learning about Database?
Paradigm shift: Data driven business environment
Customer information (e.g.,
database marketing, CRM)
Competitor andmarketplace information
Production efficienciesKnowledge and innovation
(e.g., knowledge
management, businessintelligence)
Coordination of vendors (e.g.,supply chain management
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History (1)
Early 60s
Charles Bachman introduced first general purpose DBMS known as IDS (TuringAward 1973) at General Electric (GE)
Integrated Data Store (IDS) formed the basis for N/w data model
Network Data Model was standardized by the Conference on Data SystemsLanguages (CODASYL).
Late 60s
IBM developed IMS
Information Management Systems (IMS) formed basis for Hierarchical DataModel
Hierarchichal Data Model
SABRE system for making airline reservation jointly by IBM and American
Airlines (allowed several people to access the same data thro computer N/W) 70s
Edgar Codd, at IBM proposed Relational Data Model (Turing Award 1981)
Use of DBMSs for managing corporate data became standard practice
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History (2)
80s
Relational Data Model became dominant DBMS paradigm
SQL query language for relational DBs developed as part of IBMs System R
projectis now the standard query language
Transaction Management (concurrent execution of db programs) (James Gray,
Turing Award 1999)
Now Object-oriented Data Model
Data warehouse and data mining
Accessing databases through the web/internet
Multimedia data
Text data (information retrieval)
Structure of the data (XML)
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Traditional File-Based System
Definition:
"A collection of application programs that perform services for the end-userssuch as the production of reports. Each program defines and manages its
own data."
PayrollOperating
expenses
Customer
transactionsVendorsInventory
Program Program Program Program Program
Report Report Report Report Report
One fi le, one application
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Data Redundancy
Customer Order File
Invoice number
Customer account number
Customer name, address, city, state, zip code
Order date
Product code, product description, price, unit
Customer Account File
Account Number
Customer name, mailing address, city, state, zip code
Customer Mailing List File
Customer name, mailing address, city, state, zip code
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File-Based Systems
Records contain logically related data
Limitations:
Separation and isolation of data (one file, one program)
Duplication of data Loss of data integrity - uncertainty of the correctversion of data and no
consistency
Data dependence - application program defines the data
Incompatibility of file formats
Fixed queries/proliferation of application programs - little flexibility inmeeting changing information needs
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Database
Data and
DataDefinitions
Applications
A shared collection of logically related data (and a description of this
data), designed to meet the information needs of an organization.
SeparationCentral Repository
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Data Abstraction
Separation between the datas structure (definition) and the application
programs
Data andData
Definitions
Applications
CentralRepository
DBMS
Application programs can be runon either the clients or server
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Organizing Data
Entity - distinct object (i.e., person, place, thing, concept or event)
Attribute - describes some aspect of the entity (object)
Property of the entity
Relationship - association between entities
Customers
Account_number
NameAddress
Purchases
Invoice_number
Account_numberPurchase_date
Attributes
Relationship
Entity Entity
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Database
Customer
OrdersOrder Items
Manufacturers
Products
DBMS
Management
Queries
ApplicationPrograms
Other
Software
DDL
DML
Controlled accessCentral Repository
(Organizational resource) Single Access Point Multitude of
Applications
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Advantages of the Database Approach
Control of data redundancy
Data consistency
Efficient data access, Greater informational gain, more information from the
same amount of data
Sharing data, organizational resource (i.e., shared resource)
Improved data integrity, validity and consistency
Improved access and security
Enforcement of standards
Concurrency Access and Crash recovery
Data Administration
Reduced Application development time
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Database Applications
Traditional database applications (banks, library catalogs, inventory, airlines,
universities)
Multimedia databases (images)
Geographic information systems
Data warehouse and online analytical processing (OLAP)
Real time and active database technology (sensor systems, safety-critical
systems)
World wide web (e-commerce, internet banking)
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DBMS Available
ORACLE
DB2by the IBM
MS-SQL
Teradata
Sybase
Informix
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Data Model
Collection of high level data description constructs that hide many low-levelstorage details
Semantic data model
More abstract, high level data model (makes it easier to describe about the data)
Widely used one is ER modelpictorially denotes entities and relationshipsamong them
Relational Model Relationset of records
Schema
A description of data in terms of a data model is schema
Schema for a relation specifies its name, name of each field (or attribute or
column) and type of each field. Example
Students(sid: string, name: string, login: string, gpa: real)
Each row in the relation is a record that describes the student
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Other Data Models
Relational Data model ( dominant model)
Hierarchical data model
Network model
Objectoriented model
Objectrelational model
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Types of Database Models
HIERARCHICAL
RELATIONAL
TABLEROW
COLUMN
VALUE
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Database Architecture/ Levels of Data Abstractions
Internal level
(storage view)
Conceptual level(community user view)
External level(individual user
views)
Database
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Conceptual Schema
Describes data in terms of the data model of the DBMS.
In a RDBMs, the conceptual schema describes all relations that are stored in the
database. Eg. University Db
Students (sid: string, name: string, gpa: real)
Faculty (fid: string, fname: string, sal: real)
Physical schema Specifies additional storage details
Summarizes how the relations described in conceptual schema are actually stored
on secondary storage devices like disks and tapes
Decide on what file organizations to use to store relations and indexes to speed
up data retrieval operations
External Schema
Allow data access to be customized at the level of individual users or groups of
users.
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An Example of the Three Levels
SNo FName LName Age Salary
SNo FName LName Age Salary
SNo LName BranchNo
struct STAFF {
int staffNo;
int branchNo;
char fName[15];char lName[15];
struct date dateOfBirth;
float salary;
struct STAFF *next;
/* pointer to next Staff record
*/};
index staffNo; index branchNo;
/* define indexes for staff */
BranchNo
Conceptual View
External View1
Internal View
External View2
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Database Design Phases
DATA ANALYSIS
Entities - Attributes - Relationships - Integrity Rules
LOGICAL DESIGN
Tables - Columns - Primary Keys - Foreign Keys
PHYSICAL DESIGN
DDL for Tablespaces, Tables, Indexes
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Data Independence
Ability to change one schema level without affecting the higher levelschemas
Physical Data Independence
Ability to change physical schema or internal schema without affecting
conceptual or logical schema
Logical Data Independence
Ability to change logical schema without affecting External or view schema.
(application programs)
One imp. Adv of DBMS is data independence
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Characteristics of the DB approach (1)
Single repository of data defined once, maintained and accessed by users
Self-describing nature of DB
DB + description of DB structures and constraints
stored in primary DB metadata (stored in catalog)
DBMS software works with any number of DB applications
Insulation between programs and data, and data abstraction
Program--data independence Program--operation independence (OO DBMS)
Abstraction: conceptual representation of data, no details of how data is stored
or operators are implemented
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Characteristics of the DB approach (2)
Data model
Relational data model
Object-oriented data model
Entity-relationship data model
Support multiple views of data
view = subset of DB
virtual data derived from DB (not explicitly stored)
Sharing data and multi-user transaction processing
Concurrency control
Online transaction processing (OLTP)
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Query Languages
Query questions involving data stored in dbms
Relational Algebra
formal query language based on collection of operators for manipulating
relations
Relational Calculus
formal query language based on mathematical logic
DDL: Data Definition Language
Defines db structure
Commands used are for creating, altering, query data
DML: Data Manipulation Language For manipulating (inserting, deleting, updating) db contents
Procedural and Nonprocedural (Declarative) DML
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Types of DML
Procedural DML Must be embedded in a programming language. Searches for and retrieves
individual db records and uses looping and other constructs of the host
programming language to retrieve multiple records
Non-Procedural or Declarative DML Can be used as a stand-alone query language or can be embedded in a
programming language. Searches for and retrieves information from
multiple related db records in a single command
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Components of a Database Environment
Hardware
Software: DBMS, application program and query software
Data: Organized in a schema, partitioned into subschemas
Procedures: Govern the design, access and use of the database
People: Administrators (DA, DBA), designers (logical and physical),
application developers and users (novice and high-powered)
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Database System
Stored Data Defn.Stored Database
Software to access stored data
Software to process queries/programs
DBMS
Software
Application Programs/Queries
Users
DATABASE
SYSTEM
(META-DATA).
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Users of the Database
Day-to-day use of the DB
Database administrators (DBA)
Database designers
End-users
Casual end-users
Nave or parametric users
Sophisticated end-users
Stand-alone users
System analysts and application programmers (software engineering)
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Implications of the DB approach
Potential for enforcing standard
Reduce application development time
Flexibility
Availability of up-to-date info
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When not to use a DBMS
Unnecessary overhead costs Security, concurrency control, recovery and integrity
High initial investment in hardware, software, training
DB and applications are simple, well defined, not expected to change
Real-time requirements not met (due to overhead)
Multi-user access not required
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