System design

System Design
System Analysis And Design
By:12BS(CS)02
17th October 2014
Computer Science Department , QUEST

Overview
 System Design
 Physical and Logical Design
 Designing Database
 Designing Form and Report
 Designing Interface and Dialogue
2 12bs(cs)02 System Analysis And Design 18 October 2014

Physical And Logical Design
Physical Design is a graphical representation of a
system showing the system’s internal and external
entities, and the flows of data into and out of these
entities.
An internal entity is an entity (person, place, or thing)
within the system that transforms data. Internal entities
include, for example, accounting clerks (persons),
departments (places), and computers (things).
Whereas, an external entity is an entity (person, place,
or thing) outside the system that transforms data.

Cont…
The physical portion of systems design can generally
be broken down into three sub-tasks
User Interface Design is concerned with how users
add information to the system and with how the
system presents information back to them.
Data Design is concerned with how the data is
represented and stored within the system.
Process Design is concerned with how data moves
through the system, and with how and where it is
validated, secured and/or transformed as it flows into,
through and out of the system.

Cont…
Logical Design is a graphical representation of a
system showing the system’s processes and the flows
of data into and out of the processes. We use logical
design to document information systems because we
can represent the logical nature of a system-what
tasks the system is doing, without having to specify
how, where or by whom the tasks are accomplished.
To represent the logical design of a system we can use
different diagrams like Entity- Relationship Diagram.

Database Design

Designing Database
The database design phase is divided into three steps:
1)conceptual database design
2) logical database design
3) physical database design
Conceptual Database Design
Once all the requirements have been collected and analyzed,
the next step is to create a conceptual schema for the
database, using a high level conceptual data model.The result
of this phase is an Entity-Relationship (ER) diagram or UML
class diagram.
It describes how different entities (objects, items) are related
to each other. It also describes what attributes (features) each
entity has. It includes the definitions of all the concepts
(entities, attributes) of the application area.

Database Design
Logical Database Design
The result of the logical design phase (or data model
mapping phase) is a set of relation schemas. The ER
diagram or class diagram is the basis for these relation
schemas.
There are rules how the ER model or class diagram is
transferred to relation schemas.
The relation schemas are the basis for table
definitions. In this phase (if not done in previous
phase) the primary keys and foreign keys are defined.

Database Design
Normalization
Normalization is the last part of the logical design. The goal
of normalization is to eliminate redundancy and potential
update anomalies.
Redundancy means that the same data is saved more than
once in a database. Update anomaly is a consequence of
redundancy. If a piece of data is saved in more than one
place, the same data must be updated in more than one
place.
Normalization is a technique by which one can modify the
relation schema to reduce the redundancy.

Designing Database
Physical Database Design
The goal of the last phase of database design,
physical design, is to implement the database. At this
phase one must know which database management
system (DBMS) is used. For example, different
DBMS's have different names for data types and have
different data types.
The SQL clauses to create the database are written.
The indexes, the integrity constraints (rules) and the
users‘ access rights are defined.

Designing Database
Application Design
In the application design phase, the design of the user interface
and the application programs that use and process the
database are defined and designed.
Prototyping
The purpose of a prototype is to allow the users to use the
prototype to identify the features of the system using the
computer
There are horizontal and vertical prototypes.
A horizontal prototype has many features
(e.g. user interfaces) but they are not
working. A vertical prototype has very
few features but they are working.

Designing Database
Implementation
During the implementation phase, the physical realization
of the database and application designs are to be done.
This is the programming phase of the systems
development.
Data Conversion and Loading
This phase is needed when a new database is replacing an
old system. During this phase the existing data will be
transferred into the new database.
Testing
Before the new system is going to live, it should be
thoroughly tested. The goal of testing is to find errors! The
goal is not to prove the software is working well.

Designing Database
Operational Maintenance
The operational maintenance is the process of
monitoring and maintaining the database system.
Monitoring means that the performance of the system
is observed. If the performance of the system falls
below an acceptable level, tuning or reorganization of
the database may be required.
Maintaining and upgrading the database system
means that, when new requirements arise, the new
development lifecycle will be done.

Designing Forms and Reports

Designing Forms and Reports(Cont…
Form
 A business document that contains some predefined
data and may include some areas where additional
data are to be filled in
 An instance of a form is typically based on one
database record
Report
 A business document that contains only predefined
data.
 A passive document for reading or viewing data.
 Typically contains data from many database records or
transactions.

Designing Forms and Reports(Cont…
 Is user-focused activity that follows a prototyping
approach
 First steps are to gain an understanding of the
intended user and task objectives by collecting initial
requirements during requirements determination
Requirement Determination
 Who will use the form or report?
 What is the purpose of the form or report?
 When is the report needed or used?
 Where does the form or report need to be delivered and
used?
 How many people need to use or view the form or report?

Formatting for Form and Report Design
 Meaningful titles: clear, specific, version information,
current date
 Meaningful information– include only necessary
information, with no need to modify
 Balanced layout: adequate spacing, margins, and
clear labels
 Easy navigation system: show how to move forward
and backward, and where you are currently

Formatting for Form and Report Design
A poor form design A better form design

Highlighting Information
 Notify users of errors in data entry or processing
 Provide warnings regarding possible problems
 Draw attention to keywords, commands, high-priority
messages, unusual data values
Methods For Highlighting
Highlighting can include use of
upper case, font size differences,
bold , italics , underline , boxing,
blinking , reverse video ,audible
tones , offsetting nonstandard
information and other approaches.

Guidelines for Displaying Text
 Case: mixed upper and lower case, use conventional
punctuation
 Spacing: double spacing if possible, otherwise blank
lines between paragraphs
 Justification: left justify text, ragged right margins
 Hyphenation: no hyphenated words between lines
 Abbreviations: only when widely understood and
significantly shorter than full text

Guidelines for Displaying Text
A poor help screen design A better help screen design

Guidelines for Tables and Lists
Labels
 All columns and rows should have meaningful labels.
 Labels should be separated from other information by
using highlighting.
 Redisplay labels when the data extend beyond a single
screen or page.
Formatting columns, rows and text
 Sort in a meaningful order.
 Place a blank line between every five rows in long columns.
 Similar information displayed in multiple columns should be
sorted vertically.
 Columns should have at least two spaces between them.

Guidelines for Tables and Lists (cont.)
 Allow white space on printed reports for user to write
notes.
 Use same family of typefaces within and across
displays and reports.
 Avoid overly fancy fonts.
Formatting numeric, textual and alphanumeric data
 Right justify numeric data and align columns by
decimal points or other delimiter.
 Left justify textual data. Use short line length, usually
30 to 40 characters per line.
 Break long sequences of alphanumeric data into small
groups of three to four characters each.

Guidelines for Tables and Lists (cont.)
A poor table design A better table design

Usability
Overall evaluation of how a system performs in supporting
a particular user for a particular task
There are three characteristics
 Speed
 Accuracy
 Satisfaction
Guidelines for Maximizing Usability
 Consistency: of terminology, formatting, titles, navigation,
response time
 Efficiency: minimize required user actions
 Ease: self-explanatory outputs and labels
 Format: appropriate display of data and symbols
 Flexibility: maximize user options for data input according
to preference

Designing Interface And Dialog

Designing Interface And Dialogue
Interface design An interface is a method by which users
interact with information systems.
Dialogue design A dialogue reflects the sequence of
interaction between a user and a system .
 The design of interface and dialogues is the process of
defining the manner in which human and computers
exchange information. Similar to designing f&r, the process
of designing I&d is user focused activity
 To design usable i&d you must answer the same who,
what, when, where and how

Methods of Interacting
Command Language Interaction
Users enter explicit statements into a system to invoke
operations
Example from MS DOS:
COPY C:PAPER.DOC A:PAPER.DOC
This copies a file from C: drive to A: drive
Menu interaction
List of system options is provided and a specific
command is invoked by user selection of a menu
option.
Pop-up menu: menu placed near the current cursor
position.

Methods of Interacting(cont…)
Drop-down menu: a menu-positioning method that
places the access point of the menu near the top line of the
display.

Pop-up menu

Drop-down menu

Guidelines for Menu Design
 Wording: meaningful titles, clear command verbs, mixed
upper/lower case.
 Organization: consistent organizing principle.
 Length: all choices fit within screen length.
 Selection: consistent, clear and easy selection methods.
 Highlighting: only for selected options or unavailable
options.

Contrasting Menu Designs

Form interaction: data fields are formatted in a
manner similar to paper-based forms.
Allows users to fill in the blanks when working with a
system.
Measures of an effective design:
 Self-explanatory title and field headings
 Fields organized into logical groupings
 Distinctive boundaries
 Default values
 Displays appropriate field lengths
 Minimizes the need to scroll windows

Object-based interaction: symbols are used to represent
commands or functions.
Icons graphical pictures that represent specific functions
within a system.
Use little screen space and are easily understood by users.

Natural language interaction
Inputs to and outputs from a computer-based
application are in a conventional spoken language
such as English.
Both keyboard and voice entry

Designing Interfaces
Use standard formats similar to paper-based forms
and reports.
Left-to-right, top-to-bottom navigation.
Flexibility and consistency:
 Free movement between fields
 No permanent data storage until the user requests
 Each key and command assigned to one function

Structuring Data Entry

Controlling Data Input
Objective: reduce data entry errors.
Common sources data entry errors in a field:
 Appending: adding additional characters
 Truncating: losing characters
 Transcripting : entering invalid data
 Transposing: reversing sequence of characters

Providing Feedback & Help
Three types of system feedback:
 Status information: keep user informed of what’s
going on, helpful when user has to wait for response
 Prompting cues: tell user when input is needed,
and how to provide the input
 Error or warning messages: inform user that
something is wrong, either with data entry or system
operation
Place yourself in user’s place when designing help.
Guidelines for designing usable help:
 Simplicity - Help messages should be short and to
the point.
 Organize - Information in help messages should be
easily absorbed by users
 Show - It is useful to explicitly show users how to
perform an operation.

Designing Dialogues
Dialogues: the sequence of interaction between a user and a
system. Dialogue design involves:
 Designing a dialogue sequence
 Building a prototype
 Assessing usability
Guidelines for Dialgoue Design
 Consistency (same terminology on all screens)
 Shortcuts and Sequence (special keys can be used for advanced
users)
 Error Handling(errors should be detected and reported)
 Reversal (reverse action)
 Feedback (for very user action, eg: record is added)
 Closure (e.g.: indication of first or last screen)
 Control (consistent response time)
 Ease (e.g.: transitions to first and last screen)

Designing Dialogues
Dialogue diagramming is a formal method for
designing and representing human computer
dialogues using box and line diagram
The three section of the box are used :

Designing Interfaces and Dialogues in
Graphical Environments
Two rules repeatedly emerge as comprising the first step to
becoming an effective GUI designer :
 Become an expert user of the GUI environment
 Understand the available resources and how they can be
used.
Common properties of Windows and forms in GUI
environment that can be active or inactive :
 Modality
 Resizable
 Movable
 Minimize
 Maximize
 System menu

Common Errors when designing the interface
and dialogues of website
 Opening new browser window
 Breaking or slowing down the back button
 Complex URLs
 Orphan pages
 Scrolling navigation pages
 Lack of navigation support
 Hidden links
 Links that don’t provide enough information
 Buttons that provide no click feedback

THANKYOU 

System design

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