Transcript What is a Database Management System?

An Introduction to database system
Database Management
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Basic Definitions
• Data: Meaningful facts, text, graphics,
images, sound, video segments.
• Database: An organized collection of
logically related data.
• Information: Data processed to be useful in
decision making.
• Metadata: Data that describes data.
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What is a DataBase system?
(DB)
• It is a logically coherent collection of data
with inherent meaning.
• It represents a miniworld, and should
represent the state of that world accurately.
• It is managed by a database management
system (DBMS).
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What is a DataBase Management System?
(DBMS)
• A (large) piece of software which provides an
interface between the user or application
program and the stored data.
• A DBMS is developed according to a particular
data model.
• Some example DBMSs are:
– IMS, DB2, Oracle, Sybase, Informix, SQL
Server, Access, FoxPro, O2.
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The functionality of DBMS
• Manages very large amounts of data.
• Supports efficient access to very large
amounts of data.
• Supports concurrent access to very large
amounts of data.
• Supports secure, atomic access to very large
amounts of data.
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Several basic concepts
• Data models
– A data model is a way of representing (part of)
the world.
– The principle current data model are:
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Hierarchical
Network
Relational
Object-oriented
E-R
Semantic
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Several basic concepts
• Database design
– Design goals
• Minimize redundancy in order to eliminate the
modification anomalies in database.
• Represent the situation accurately
– Design Stages
• Conceptual (product independent)
• Logical (product specific)
• Physical / Implementation (product specific)
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Database Development Activities
Enterprise Modeling
Conceptual Data Modeling
Logical DB Design
Physical DB Design
DB Implementation
DB Maintenance
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The stages
focused
in COP4540
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Conceptual Database Modeling
• Determine user requirements.
• Determine business rules.
• Build conceptual data model
– outcome is an entity-relationship diagram or
similar communication tool.
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Logical Database Design
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Select logical database model.
Map Entity-Relationship Diagrams
Normalize data structures.
Specify business rules.
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Physical Database Design
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Select DBMS
Select storage devices
Determine access methods
Design files and indexes
Determine database distribution
Specify update strategies
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Several basic concepts
• Schema
– Logical structure of the data defined by using
data definition language (DDL).
• Queries
– A “query” is a database lingo for a question
about the data.
– A “query” is composed by using query
language (QL)
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The architecture of database system
Users / Programmers
Application Programs / Queries
Database Management System
1. Software to process
queries/programs
2. Software to access stored
data
Stored data
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Components of the Database Environment
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CASE Tools
Repository
Database Management System (DBMS)
Database
Application Programs
User Interface
Database Administrators (DBA)
System Developers
End Users
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Evolution of Database Systems
• Hierarchical and Network (Legacy): Data are
modeled as linked records.
• Relational: Data are modeled as related tables.
• Object-oriented: Data are organized as linked
objects.
– Object-relational: Integration of relational and
object-oriented features.
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RDBMS and SQL
• RDBMS is a DBMS on the basis of relational
model.
• It is the most popular type of the DBMS.
• The data is organized as tables called relations
• Two famous systems:
– System R at IBM & Ingres at UC Berkeley
• SQL (Structured Query Language)
– the most important query language based on relational
model.
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RDBMS and SQL
Accounts
accountNo
balance
type
12345
1000.00
savings
67890
2846.92
checking
SELECT balance
FROM
Accounts
WHERE accountNo = 67890
Result:
2846.92
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Disadvantages of File Processing
Systems
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Data Dependence
Data Redundancy (Duplication of data)
Limited Data Sharing
Lengthy Development Times
Excessive Program Maintenance
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Advantages of Database Approach
• Program-Data Independence: No need to
rewrite programs when data is modified
• Minimal Data Redundancy
• Improved Data Consistency
• Improved Data Sharing
• Increased Application Development
Productivity.
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Advantages of Database Approach
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Enforcement of Standards
Improved Data Quality (Constraints)
Better Data Accessibility/Responsiveness
Reduced Program Maintenance
Security, Backup/Recovery, Concurrency
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Costs and Risks of the Database
Approach
• New, Specialized Personnel
• Installation Management Cost and
Complexity
• Conversion Costs
• Organizational Conflict
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