Database Design

Essentials of
Database Design

Database Design
It can be used to describe many different
parts of the design of an overall database
system
Principally, and most correctly, it can be
thought of as the logical design of the
base data structures used to store the
data

Database Design
 In the relational model these are the tables and
views. In an object database the entities and
relationships map directly to object classes and
named relationships
 However, the term database design could also be
used to apply to the overall process of designing,
not just the base data structures, but also the
forms and queries used as part of the overall
database application within the database
management system

Database Design
The process of doing database design
generally consists of a number of steps which
will be carried out by the database designer.
Usually, the designer must:
Determine the relationships between the different
data elements
Overlay a logical structure upon the data on the
basis of these relationships

ER Diagram (Entity Relationship Diagram)
Database designs also include ER (entity-relationship
model) diagrams
An ER diagram is a diagram that helps to
design databases in an efficient way
Attributes in ER diagrams are usually modeled
as an oval with the name of the attribute, linked
to the entity or relationship that contains the
attribute

A Sample
Entity-relationship Diagram

Database design process
1. Determine the purpose of the database -
This helps prepare for the remaining
steps
2. Find and organize the information
required - Gather all of the types of
information to record in the database, such
as product name and order number

3. Divide the information into tables - Divide
information items into major entities or subjects,
such as Products or Orders. Each subject then
becomes a table
4. Turn information items into columns - Decide
what information needs to be stored in each
table. Each item becomes a field, and is
displayed as a column in the table. For
example, an Employees table might include
fields such as Last Name and Hire Date

5. Specify primary keys - Choose each table’s
primary key. The primary key is a column, or a
set of columns, that is used to uniquely identify
each row. An example might be Product ID or
Order ID.
6. Set up the table relationships - Look at each
table and decide how the data in one table is
related to the data in other tables. Add fields to
tables or create new tables to clarify the
relationships, as necessary.

Primary Key
and table
relationship
in a database

7.Refine the design - Analyze the design for
errors. Create tables and add a few records
of sample data. Check if results come from
the tables as expected. Make adjustments
to the design, as needed.
8. Apply the normalization rules - Apply the
data normalization rules to see if tables are
structured correctly. Make adjustments to
the tables

Designing Inputs,
Outputs and Control

Input Integrity Controls
 Use with all input mechanism from specific
electronic device to standard keyboard inputs
 Additional level of verification that helps reduce
errors on input data
 For example a system need a certain amount of
information for a valid entry, but an input device
cannot ensure that all the necessary fields have
been entered
 An additional level of verification, which will call a
control is necessary to check for completeness

Common input control techniques
Error Detection and Elimination
 Field Combination Control. Verifies data in
one field based on data in another field or
fields
Value limit Control. Identify when a value in a
field is too large or too small
Completeness Control. Ensures all necessary
fields in an input form have been entered
Data validation Control. Validate the input data
for correctness and appropriateness

Common input control techniques
Transaction Logging
A technique by which any update to the
database is logged with audit information
such as user ID, date, time, input data, and
type of update
So that it can trace any errors or problems
that occur. The more advanced database
systems- such as those that run on servers,
workstations, and mainframes

Common Input Control techniques
Transaction Logging
It has 2 main objective:
 Helps discourage fraudulent transactions, If person
knows that every transaction is logged, then that
person is less apt to attempt a fraudulent
transaction
 Provide recovery mechanism for erroneous
transaction, more sophisticated systems can
provide a “before” and “after” image of he field
that are change by the transaction, as well as audit
trail of all transactions. Typically used only for
highly sensitive or critical data files, but they do
represent an important control mechanism that is
available when necessary

Output Integrity Control
Output from a system comes in various
forms such as output that is used by
other systems, printed reports, and
data output on computer screens.
The main purpose of it is to ensure
that output arrives at the proper
destination and is correct,
accurate, current, and complete.

Destination Control
 Ensure that output information is channeled to the
correct person
Systems with good controls printed
destination and routing information on a
report cover page along with the report
Today ,business accomplish the same
function of a control desk by placing
printers in each of the locations that need
printed reports

Completeness, Accuracy and
Correctness Control
This are the main function primarily of the
internal processing of the system rather than
any set of controls
To ensure this, printing of control fields on
the output report
Every report must have a date and time
stamp, both for the time the report was
printed and the date of the report is
reprinted due to previous error

Completeness, Accuracy and
Correctness Control
The following items are controls that should
be printed on reports:
 Date and time of report printing
 Date and time of data on the report
 Time period covered by the report
 Beginning header with report identification and
description
 Destination of routing information
 Pagination in the form “page-of-”
 Control totals and cross footings
 “End of Report” trailer
 Report version number and version date

Design of System Inputs
When designing inputs for the
system, the system developer
must perform four tasks:
o Identify the devices and mechanisms
that will be used to enter inputs
o Identify all system inputs and develop a
list with data content of each
o Design and prototype the electronic
forms(the window the user works with)
and other inputs

Design of System Inputs
Identifying Device Mechanism
 Often when analysts begin developing a system,
they assume that all input will be entered via
electronic, graphical forms because they are now
so common on a personal computers and
workstations
 All data must be error-free, it must be validated;
avoid reentering the information as much as
possible avoid human involvement

Identifying device mechanism
Devices that allow data captured without
human keystroking:
Magnetic Card strip readers
Bar Code readers
Optical-character recognition reader and
scanner
Touch screens and devices
Electronic pens and writing surfaces
Digitizers, such as digital cameras and
digital audio devices

Developing list of Inputs
and data requirement
Provides check of the quality of analysis
models
It also identify the flows that cross the
system boundary
Analysis Model: Structured approach and
Object Oriented Approach

Structured Approach
The first task is to define the automation
boundary
The point is not all processing done with
computer, However, the input data flows
crossing the boundary are clearly defined,
so the required inputs will be the new order
information data flow

DFD showing
automation boundary

Sequence diagrams identify each incoming
message, and the Design class diagrams
contain the pseudocode to verify the
characteristic of the input

Sequence diagram

Design class diagrams

Designing and
Prototyping Input Forms
Good design principles dictate that the
paper form and its electronic
counterpart should have the same
general layout and sequence of data
fields
In other words, this will be use to
enter the information into the system

Designing of System Outputs
Determining type of output
Making list of specific reports
based on the application design
Designing and prototyping reports

Determining Type of Output
Detailed Report
Carry out the day-to-day processing of the
business, contain detailed information about the
transaction
Summary Report
Recaps or summarize detailed information over
a period of time or some category
Exception Report
A Report that contains only information about
nonstandard, conditions
Executive Report
A report use for information resources that is
normally used for strategic decisions

Making list of specific report
oThe objective is to ensure that each of
the required outputs from the system is
specified correctly
oWhereas the data content of the input
forms must support the needs of the
database, the data content of the
outputs must support the information
requirements of the report users.

Designing and Prototyping Reports
o Key principles during design of output reports:
What is the objective of the report? Who is the
intended audience?
o Designer must decide on the level of detail and
format of the report, they can decide if they know
the objective of the report
o Labels and headings should be used to ensure the
correct interpretation of the report data and
make sure that every report must have a
meaningful title to indicate data content.

Output Design Objectives
 Output is information delivered to users through
information system by the ways of networks
 Some data require extensive processing before they
become suitable output
 Output can take many forms; Traditional hard copy
of printed reports and soft copy such as computer
screens, microforms and audio output
 To create most useful output possible, system
analyst works closely with the user through an
interactive process until the result is considered to
be satisfactory

6 Objectives for Output Design
 Designing output to serve a specific purpose
 Making output meaningful to the user
 Delivering the appropriate quantity of output
 Providing appropriate output distribution
 Providing output on time
 Choosing the most effective output method

Objectives for Output design
Designing output to serve a specific purpose
o Output is designed based on the
purpose that the system analyst find
out during information requirement
determination phase of analysis

Designing output to fit the user
o It is more practical to create user-specific or user-customizable
output when designing for a decision
support system or highly interactive applications
such as those mounted on the web
o On the basis of interview, observation, cost
considerations and perhaps prototypes, it will be
possible to design output that addresses what
many, if not all, users need and prefer.

Delivering appropriate Quantity of Output
o More is not always better, especially where the
amount of output is concerned. Part of the task of
designing output is deciding what quantity of
output is correct from users
o The Problem with information overload is so
prevalent as to have become a cliché, but it
remains a valid concern
o No one is served if excess information is given
only to flaunt the capabilities of the system

Making sure the output is where it is needed
o Output is often produced at one location(for
example, in the data-processing department)
and then distributed to the user
o Appropriate distribution is still an important
objective for the system analyst, to be used
and useful, output must be presented to the
right user

Providing output on time
o Many reports are required on a daily basis,
some only monthly, other annually, and others
only by exception
o Using well-publicized Web-based output can
alleviate some problems with the timing of
output distribution as well. Accurate timing of
output can be critical to business operation

Choosing the right output method
o Output can come in many forms,
with the movement to online
systems, much output now appears
on display screen, and users have
the option of printing it out with
their own printer.

Output Technologies
Printer
Advantages: Affordable in most organization
Flexible in time, location, and capabilities
Handles large volume of outputs
Reaches many inexpensively
Highly reliable with little down time
Disadvantages: May be noisy, Compatibility problems
with computer software, May require special,
expensive supplies, Still requires operator intervention,
Depending on model, may be slow

Output Technologies
Display Screen
Advantages: Interactive, Works online, real-time
transmission, Quiet, Takes advantage of
computer capabilities for movement within
databases and files, Good for frequently
accessed
Disadvantages: Require cabling and setup space, Still
may require printed documentation, Can be expensive
if required for many users

Output Technologies
Audio Output
Advantages: Good for individual user, Transient
message, worker needs hands free, output is
highly relative
Disadvantages: Expensive to develop, needs dedicated
room where output will not interfere with other tasks,
has limited application

Output Technologies
DVD, CD-ROM, and CD-RW
Advantages: Has large capacity, Allow
multimedia output, has speedy retrieval, less
vulnerable to damage
Disadvantages: Expensive to develop, more difficult to
use on a network

Output Technologies
Electronic Output (email, faxes, and web pages)
Advantages: Reduces paper, can be updated
very easily, Eliminates “telephone tag”, can be
“broadcast”, can be more interactive
Disadvantages: Has generally lower resolution, Not
conducive to formatting, difficult to convey context of
messages (email), Web sites need diligent maintenance

Factors to considered
when choosing output technology
1. Who will use the output(requisite quality)?
2. How many people need the output?
3. Where is the output needed (distribution/ logistics)?
4. What is the purpose of output?
5. What is the speed with which output is needed?
6. How frequently will the output be accessed?
7. How long will(or must) the output be stored?
8. Under what special regulation is the output produced, stored, and
distributed?
9. What are the initial and ongoing costs of maintenance supplies?
10. What are the environmental requirements (noise absorption, controlled
temperature, space for equipment, and cabling) for output technologies?

Database Design

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Database Design

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