CHAPTER 1
Databases and Database Users
Introduction
Traditional database applications: The information
is stored and accessed is either textual or numeric.
New applications:
Multimedia databases: store pictures, video, …
Geographic information systems (CIS) can store
and analyze maps, weather data, …
Data warehouses is used in many companies to
extract and analyze information.
Real-time & active database is used in controlling
industrial and manufacturing processes.
Basic Definitions
Database: A collection of related data.
Data: Known facts that can be recorded and have
an implicit meaning.
Example:
Names, telephone numbers, addresses, …
Mini-world: Some part of the real world about
which data is stored in a database.
Example:
Student grades and transcripts at a university.
Basic Definitions
Database
Management System (DBMS): A
software package/ system to facilitate the creation
and maintenance of a computerized database.
Database System: The DBMS software together
with the data itself.
Example of a Database
Example of a Database
Mini-world for the example:
Part of a UNIVERSITY environment.
Some mini-world entities:
- STUDENTs
- COURSEs
- SECTIONs (of COURSEs)
- (academic) DEPARTMENTs
- INSTRUCTORs
Example of a Database
Some mini-world relationships:
- SECTIONs are of specific COURSEs
- STUDENTs take SECTIONs
- COURSEs have prerequisite COURSEs
- INSTRUCTORs teach SECTIONs
- COURSEs are offered by DEPARTMENTs
- STUDENTs major in DEPARTMENTs
Example of a Database
Typical DBMS Functionality
Define a database: in terms of data types,
structures and constraints.
Construct or Load the Database on a secondary
storage medium.
Manipulating the database : querying, generating
reports, insertions, deletions and modifications to
its content.
Concurrent Processing and Sharing by a set of
users and programs.
Protection or Security measures to prevent
unauthorized access.
Main Characteristics of the Database
Approach
File Processing systems: Drawbacks of
using file systems
Data redundancy and inconsistency (mâu
thuẩn)
Difficulty in accessing data
Integrity problems
Security problems
Concurrent access by multiple users…
Main Characteristics of the Database
Approach
Database Approach:
Self-describing nature of a database system: A
DBMS catalog stores the description of the
database. The description is called meta-data.
This allows the DBMS software to work with
different databases.
Insulation between programs and data: Called
program-data independence. Allows changing
data storage structures and operations without
having to change the DBMS access programs.
Main Characteristics of the Database
Approach
Data Abstraction: A data model is used to hide
storage details and present the users with a
conceptual view of the database.
Support of multiple views of the data: Each
user may see a different view of the database,
which describes only the data of interest to that
user.
Sharing of Data & Multi-user Transaction
processing: allowing a set of concurrent users to
retrieve and to update the database.
Database Users
Actors on the scene: Users may be divided into
those who actually use and control the content
called “Actors on the Scene”.
Database administrators(DBAs): Responsible
for managing the database system, authorizing
access, coordinating & monitoring uses.
Database designers: Responsible for designing
the database, identifying the data to be stored,
choosing the structures to represent and store
this data.
Database Users
End Users: The persons that use the database
for querying, updating, generating, reports, etc.
Casual end users: Occasional users.(middle- or
high-level managers).
Parametric end users: They use preprogrammed canned transactions to interact
continuously with the database.
Sophisticated end users: Use full DBMS
capabilities
for
implementing
complex
applications.
Database Users
Stand-alone users (personal databases)
System
Analysts/Application programmers:
Design and implement canned transactions for
parametric users.
Workers behind the scene
DBMS designers and implementers: Design and
implement the DBMS software package itself.
Tool developers: Design and implement tools that
facilitate the use of the DBMS software. Tools
include design tools, performance tools, special
interfaces.
Operators and maintenance personnel: Work
on running and maintaining the hardware and
software environment for the database system
Advantages of Using the Database
Approach
Controlling redundancy in data storage and in
development and maintenance efforts.
Sharing of data among multiple users.
Advantages of Using the Database
Approach
Restricting unauthorized access to data.
Providing persistent storage for program Objects.
Providing Storage Structures for efficient Query
Processing
Providing backup and recovery services.
Providing multiple interfaces to different classes of
users.
Representing complex relationships among data.
Enforcing integrity constraints on the database.
Drawing Inferences and Actions using rules
When not to use a DBMS
Main inhibitors (costs) of using a DBMS:
High initial investment and possible need for
additional hardware.
Overhead for providing generality, security,
concurrency control, recovery, and integrity
functions.
When a DBMS may be unnecessary:
If the database and applications are simple, well
defined, and not expected to change.
If there are stringent real-time requirements that
may not be met because of DBMS overhead.
If access to data by multiple users is not required.
Chapter 2
Database System
Concepts and Architecture
Data Models
A set of concepts to describe the structure of a
database, and certain constraints.
A set of basic operations: retrievals and updates
on the database.
The dynamic aspect or behavior : allows the
database designer to specify a set of valid userdefined operations.
Categories of data models
High-level (conceptual data model): Provide
concepts the way many users perceive data.
Entity: real world object or concept to be
represented in database.
Attribute: some property of the entity.
Relationship: represents and interaction among
entities.
 Low-level (Physical data models): Provide
concepts that describe details of how data is
stored in the computer.
Categories of data models
Representational
(Implementation
data
models): Provide concepts that fall between the
above two, balancing user views with some
computer storage details.
Include:
Relational Data model
Network model
Hierarchical model
Schemas
Is the description of the database (not database
itself)
Specified during database design
 Not expected to change frequently
A displayed schema is called a schema diagram
Schema diagram represents only some aspects of a
schema (name of record type, data element and
some type of constraint)
Example: Each object in the schema-such as
STUDENT or COURSE-is a schema construct.
Schemas
Schemas versus Instances
Database schema: description of the data (meta-
data). Includes descriptions of the database
structure and the constraints.
 Database Instance: The actual data stored in a
database at a particular moment in time. Also
called database state (or occurrence).
Difference between schema and state:
At design time, schema is defined and state is
the empty state.
State changes each time data is inserted or
updated, schema remains the same.
Three-Schema Architecture
Internal schema at the internal level to describe
physical storage structures and access paths.
Typically uses a physical data model.
Conceptual schema at the conceptual level to
describe the structure and constraints for the
whole database for a community of users. Uses a
conceptual or an implementation data model.
External schemas at the external level to describe
the various user views. Usually uses the same data
model as the conceptual level.
Three-Schema Architecture
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.
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
Data Independence
When a schema at a lower level is changed, only
the mappings between this schema and higherlevel schemas need to be changed in a DBMS that
fully supports data independence.
The
higher-level schemas themselves are
unchanged. Hence, the application programs need
not be changed since they refer to the external
schemas.
DBMS Languages
Data Definition Language (DDL): Used by the
DBA and database designers to specify the
conceptual schema of a database.
Data Manipulation Language (DML): Used to
specify database retrievals and updates.
High Level or Non-procedural Languages: SQL,
are set-oriented and specify what data to retrieve
than how to retrieve. Also called declarative
languages.
Low Level or Procedural Languages: record-ata-time; they specify how to retrieve data and
include constructs such as looping.
Centralized Architectures
Centralized DBMS: combines everything into
single system including: DBMS software,
hardware, application programs and user interface
processing software.
Client-Server Architectures
The client-server architecture: was developed to
deal with computing environments in which a
large number of workstations, file servers,
printers, database servers, Web servers, and other
equipment are connected via a network.
Client-Server Architectures
Clients:
Provide appropriate interfaces and a client-
version of the system to access the server
resources.
Clients maybe PCs or Workstations with disks
with only the client software installed.
Connected to the servers via some form of a
network (LAN, wireless network, etc.)
DBMS Server:
Provides database query and transaction
services to the clients
Sometimes called query and transaction servers
Two Tier Client-Server Architecture
 User
Interface Programs and Application
Programs run on the client side.
 Interface called ODBC (Open Database Connectivity)
provides an Application program interface (API) allow
client side programs to call the DBMS. Most DBMS
vendors provide ODBC drivers.
• A client program may connect to several DBMSs.
• Other variations of clients are possible: in some
DBMSs, more functionality is transferred to clients
including data dictionary functions, optimization and
recovery across multiple servers,… In such situations
the server may be called the Data Server.
Two Tier Client-Server Architecture
Three Tier Client-Server Architecture
Web applications use an
architecture three-tier
architecture.
An
intermediate layer
between the client and
the
database
server,
Application Server or
Web Server
Three Tier Client-Server Architecture
Stores the web connectivity software and the
rules and business logic (constraints) part of
the application used to access the right amount
of data from the database server.
Acts like a conduit for sending partially
processed data between the database server and
the client.
Additional Features- Security:
Encrypt the data at the server before
transmission.
Decrypt data at the client.
Classification of DBMSs
Based on the data model used:
Traditional: Relational, Network, Hierarchical.
Emerging: Object-oriented, Object-relational.
Other classifications:
Single-user
(typically
used with microcomputers) vs. multi-user (most DBMSs).
Centralized (uses a single computer with one
database) vs. distributed (uses multiple
computers, multiple databases)
Classification of DBMSs
Distributed Database Systems have now come to
be known as client server based database
systems because they do not support a totally
distributed environment, but rather a set of
database servers supporting a set of clients.