Information Systems
(ත ොරතුරු පද්ධති)
Lesson 05 - Part - 02
(System Analysis & Design)
Objectives – Learning Outcomes
The objectives of this section are to get knowledge on
system design phase.
When you have followed this section you will:
• Understand about logical data modeling
• Demonstrate Process specification
• Understand to define Business system options
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Objectives – Learning Outcomes
• Understand to Identify the concept of Logical
Design
• Understand about logical data structures
• Understand to Describe the Process specification,
Data dictionary and Interface design
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Outline
- Logical Design
- Business system options
- Process specification
- Data dictionary
- Interface design
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Logical Design
• In SSADM the vehicle for analysing the logical
structure of an organisation’s information is the
Logical Data Model (LDM).
• A Logical Data Model is a way of graphically
representing what that information is really all
about, how it relates to other information and
business concepts, and how business rules are
applied to its use in the system.
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Logical Design
• The LDM is possibly the most important and
ultimately the most rigorous product of an
entire SSADM project.
• Logical Data Models consist of two parts:
– a diagram called the Logical Data Structure (LDS);
– a set of associated textual descriptions that explain
each part of the diagram.
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Logical Design - Example
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Business System Options
• Business Systems Options (BSOs) provide a
range of possible solutions for the business to
consider.
• Each BSO may have more than one way of
being implemented technically. These are
known as Technical System Options (TSOs)
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Business System Options Cont.
Contents of a Business Systems Options Report
• The degree of automation
• The boundary between the system and the
users
• The distribution of the system, for example, is
it centralized to one office or spread out
across several?
• Cost/Benefit analysis
Business System Options Cont.
Contents of a Business Systems Options Report
• Development time scale
• Known technical constraints
• Organisation of the system - types of access (on-
line or off-line), interfaces with other systems
• Approximate data and transaction volumes
• Training requirements
• Benefits & impact on the organisation
Business System Options Cont.
• Up-to 3 shortlisted. Each Option presented
formally to the management.
• Strengths & Weaknesses explained to facilitate a
decision.
• Opportunity to reassess the viability of the
project (to carry on / cancel it).
• Selected BSO could be one option or an hybrid.
• Document selected BSO (reasons for selection &
rejection others).
• Form the basis for the rest of the project and for
the final system.
Process Specification
• A process specification is a method used to
document, analyze and explain the decision-
making logic and formulas used to create
output data from process input data
• Created for primitive processes as well as for
some higher level processes on a data flow
diagram
• Its objective is to flow down and specify
regulatory/engineering requirements and
procedures
Process Specification
- Uses
• Reduce process ambiguity
• Obtain a precise description of what is
accomplished
• Validate the system design
- This is not for
• Processes that represent physical input
and/or output
• Processes that represent simple data
validation
• Processes that use prewritten code
Process Specification - Example
Data Dictionary
• A data dictionary is a collection of data about
data.
• It maintains information about the definition,
structure, and use of each data element that
an organization uses.
Data Dictionary
In a relational database, the metadata in the data
dictionary includes the following:
• Names of all tables in the database and their
owners
• Names of all indexes and the columns to which
the tables in those indexes relate
• Constraints defined on tables, including
primary keys, foreign-key relationships to other
tables, and not-null constraints
Data Dictionary - Example
Interface Design
What is a System Interface
• A system transforms its inputs into its outputs.
The inputs must come from somewhere; in the
systems perspective, they always come from
some other system (in the form of that other
system's outputs). Similarly, system outputs are
made available to other systems (and become
those other systems' inputs).
• The collection of all the inputs and outputs of a
system define its interface.
Interface Design
Interface can be categorized as
• System Interface
Inputs or Outputs that require minimal
human intervention
• User Interface
System interfaces that directly involve a
system user
Interface Design
Good Interface characteristics
• User centered
• Affordance and visibility
• Consistency
• Shortcuts
• Error Handling
Interface Design - Sample Interface
Summery
In this section you have given an idea about business
system options, process specification, data dictionary and
interface design of System Analysis and Design phase.
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References
- SOFTWARE ENGINEERING, Ninth Edition, Ian Sommerville
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Lesson 06 : System Development, Testing
