INTRODUCTION TO DBMS

Contents
Definition of data, information, knowledge Definition of database, DBMS

Database vs. File systems.

Three-schema architecture Data independence

Database users
Database Administrator(DBA)

Definition of Data & information

What is data?

Known facts that can be recorded and have some implicit meaning

What is information?
Meaningful data

Definition of knowledge
What is knowledge?

knowledge indicates the information which not only

utilize in current decision making but also store for later use.
What is the difference between knowledge and

information?

Definition of Database, DBMS

What is database?

organized collection of related information presented to

serve a specific purpose

What is database management system (DBMS)? a collection of interrelated data (database)

and a set of programs to access those data and maintain database concurrently and efficiently.

Purpose of Database Systems

Limitations of File Systems
In the early days, database applications were built on top of file

systems
Data is stored in separate files Data is manipulated by a set of application programs

As time goes by, the number of files and application programs

increases
increasing complexity of database application management

Purpose of Database Systems

Limitations of File Systems
Drawbacks of using file systems to store data
Data redundancy and inconsistency
Redundancy: duplication of information in different files Inconsistency: the various copies of the same data may be different

Difficulty in accessing data

Need to write a new program to carry out each new task

Data isolation multiple files and formats

Because data are scattered in various files, and files may be in different formats, writing the appropriate information to retrieve the appropriate data is difficult

Integrity problems
Data values stored in the database must satisfy certain types of consistency constraints Integrity constraints (e.g. account balance > 0) become part of program code Those constraints are forced by the database system developer Hard to add new constraints or change existing ones

Purpose of Database Systems

Limitations of File Systems
Atomicity of updates
Failures may leave database in an inconsistent state with partial updates carried out E.g. 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 E.g. two people reading a balance and updating it at the same time

Security problems
Not every user of the database should be able to access all the data

Database systems offer solutions to all previous problems

Schema & Instance

Instance: The collection of information stored in the

database in a particular moment is called instance of database.

Schema: The overall design of the data base is schema.

Difference between them:

Instance of a database changes over time as information is inserted and deleted. Schema changes infrequently.

View of Data in a Database

The Need for Data Abstraction
A major purpose of a database system is to provide users with an

abstract view of data

The system hides certain details of how the data are stored and

maintained

The objective of data abstraction is to simplify the interaction with

the database from the user perspective

Most of database users are not computer trained

However, more complexity from the design perspective Complex data structure to represent data

View of Data in a Database

The levels of Data Abstraction
Physical Level: describes how

the data is actually stored

Describes

low

level

data
What to store

structures.
Block of consecutive storage

locations (e.g. bytes)

How to store

The compiler hides this level

of details from programmers.

View of Data in a Database

The levels of Data Abstraction
Logical Level: describes what data are stored in the database and what relationships exist between data

type customer = record name: string; street: string; city: integer; end;

each record is described by a type definition Programmers work at this level of abstraction Similar to database administrator

View of Data in a Database The levels of Data Abstraction

View Level: describes only part of the entire database.
application programs hide details of data types. Views can also hide information (e.g. salary) for security purposes. computer users only see a set of applications without details on data

types Similar to users of database

Data Abstraction

Each layer need not know how other layers organize data.

Mapping
Mappings among schema levels are needed to transform

requests and data.

Programs refer to an external schema, and are mapped by

the DBMS to the internal schema for execution.

Request for a data

External level
Request against a conceptual schema Conceptual level Request against internal schema Internal level

Data Independence
Logical Data Independence: The capacity to change the

conceptual schema without having to change the external schemas and their application programs.

Physical Data Independence: The capacity to change the

internal schema without having to change the conceptual schema.

Database Users
Users are differentiated by the way they expect to interact with the system :

those who actually use and control the content (called Actors on the Scene) and those who enable the database to be developed and the DBMS software to be designed and implemented (called Workers Behind the Scene).

Database Users
Database administrators: responsible for authorizing access
to the database, for coordinating and monitoring its use, acquiring software, and hardware resources, controlling its use and monitoring efficiency of operations.

Database Designers: responsible to define the content, the

structure, the constraints, and functions or transactions against the database. They must communicate with the end-users and understand their needs.

End-users: they use the data for queries, reports and some of
them actually update the database content.

Application Programmers: System analysts determine the

requirements of end-users and programmers implement programs, test, debug and document.

Database End-Users
1. Casual : access database occasionally when needed

2.

Nave or Parametric : invoke one of the permanent application

programs that have been written previously E.g. Bank cashier, people accessing a database over the web The typical user interface for nave user is a form interface where the user just fill in the appropriate fields of the form

Database End-Users
3. Sophisticated : these include business analysts, scientists,
engineers, others thoroughly familiar with the system capabilities. Many use tools in the form of software packages that work closely with the stored database.

4. Stand-alone : mostly maintain personal databases using ready-touse packaged applications. An example is a tax program user that creates his or her own internal database.

Database Administrators
The Database Administrator (DBA) Coordinates all the activities of the

database system
The DBA has a good understanding of the enterprises information resources

and needs

The DBA has central control over the system

Database Administrators
Database administrator's duties include:
Schema definition, specifying integrity constraints Storage structure and access method definition Schema and physical organization modification Granting user authority to access the database Acting as liaison with users Monitoring

performance

and

responding

to

changes

in

requirements Routine maintenance (DB backup, Ensuring free space for the DB, etc )

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.

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

Data dictionary
Used to store schema descriptions and other information such as data about data (metadata), design decisions, application program descriptions, user information, usage standards, etc. Active data dictionary is accessed by DBMS software and users/DBA.

Passive data dictionary is accessed by users/DBA only.

Data dictionary
A data dictionary should help a user in:
Communication with the users
Controlling data element in a simple and effective

manner Determining the impact of changes to data element on the total database Centralizing the control of a data element.

Database System Applications

Banking: all transactions Airlines: reservations, schedules Universities: registration, grades, student information Sales: customers, products, purchases Manufacturing: production, inventory, orders, supply chain Human resources: employee records, salaries, tax deductions Telecommunications: keeping record of calls made, generating
monthly bills

Architecture

catalog

Databases are self-describing: catalog describes the structure of the data stored in the DB

Client-server Architecture

Two-tier architecture: E.g. client programs using ODBC/JDBC to communicate with a database Three-tier architecture: E.g. web-based applications, and applications built using middleware