Database:
A collection of related data [Elmasri].
• A database represents some aspect of real world
called “miniworld” [Elmasri] or “enterprise”[Ramakrishnan].
• A database can be of any size and of varying
complexity.
• It may be generated and maintained manually or using
computers.
A few fundamental questions
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What data to store?
How to describe this data?
How to store this data?
How to retrieve information from the data?
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 a given data model.
View 1
The three-schema
architecture
View 2
View 3
Conceptual Schema
Physical Schema
External Schema
Conceptual Schema
Internal Schema
Example of Schemas in Relational Data Model
• Conceptual schema:
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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:
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Relations stored as unordered files, heap files, or hashed
files.
Index on first column of Students. Tree-based indexes
or hash-based indexes can be used.
• External Schema (View):
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Course_info(cid:string,enrollment:integer)
Classification of Databases
By data model
• Network Databases (early 1960s); E.g., IDS, IDMS
• Hierarchical Databases (e.g., SABRE); E.g., IBM’s IMS
• Relational (1970) Databases (RDBMS); widely used
• Object-oriented Databases (OODBMS); E.g., ObjectStore, Poet.
• Object-relational Databases (ORDBMS);
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Deductive Databases
Active Databases
Real-time Databases
Spatial Databases
Temporal Databases
Multimedia Databases
Parallel and Distributed Databases
Database Management System
(DBMS):
A software package designed to store and
manage databases.
Relational DBMSs: DB2, Informix, Oracle, Sybase, Microsoft Access,
Microsoft SQL Server, FoxBase, Paradox, Teradata, MySQL, mSQL, etc.
Advantage of DBMS:
Data Independence
• Applications insulated from how data is structured and
stored
• DBMS provides an abstract view, without exposing data
representation and storage
• DBMS also allow users to manipulate the data in a
convenient way
A1
P1
OS vs. DMBS
read/write
OS
1)
2)
Data unit (file vs table)
Data manipulation
read/write
DBMS
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1100101010…
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Advantages of DBMS:
Efficient Access
• Use indexes
– Sophisticate techniques are used to ensure efficient
store and retrieval of massive data
• Query optimization
– rewrites query for a better response time using
statistics maintained in the database management system
• Support extremely large databases
– Beyond the limitation of the underlying OS
Advantages of DBMS:
Reduce Application Development Time
• Do not need to write the database management
software for each application
• Use standard query languages to access data such
as SQL
• Use standard ways to write database applications
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JDBC for Java language
ODBC
Perl DBI
PHP
ProC
Advantages of DBMS:
Security & Integrity
• Secrecy: Users should not be able to see things
they are not supposed to.
– E.g., A student can’t see other students’ grades.
• Integrity: Users should not be able to modify
things they are not supposed to.
– E.g., Only instructors can assign grades.
• Availability: Users should be able to see and
modify things they are allowed to.
Advantages of DBMS:
Concurrency Control
• Concurrent execution of user programs is essential
for good DBMS performance.
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Because disk accesses are frequent, and relatively slow, it
is important to keep CPU working on several user programs
concurrently.
• Interleaving actions of different user programs can
lead to inconsistency.
• DBMS ensures such problems don’t arise: users can
pretend they are using a single-user system.
Structure of a DBMS
• A typical DBMS has a
layered architecture.
• The figure does not show
the concurrency control
and recovery components.
• This is one of several
possible architectures;
each system has its own
variations.
These layers
must consider
concurrency
control and
recovery
Query Optimization
and Execution
Relational Operators
Files and Access Methods
Buffer Management
Disk Space Management
DB
Career Choices in Database
Areas
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System analysts
Project managers
Database administrators
Database application developers/testers
Customer supports
Consultants
DBMS developers
Database Researchers
Database book authors
Database software instructors