This document discusses key concepts and principles of software design. It defines design as the process of applying techniques and principles to define a system in sufficient detail to allow its implementation. The goal of design is to translate requirements specified in an SRS document into a design document. Design involves data design, architectural design, interface design, and procedural design. It serves as the foundation for software engineering and maintenance. The document outlines general design tasks, objectives, goals, constraints, and criteria for a good design, emphasizing that design fosters quality and allows accurate translation of requirements into a software product.

1. DESIGN CONCEPTS & PRINCIPLES
SAVYASACHI SHARMA
MUZAFFARPUR INSTITUTE OF TECHNOLOGY
Muzaffarpur4/11/2020 1

2. DESIGN - Definition
• The process of applying various techniques and
principles for the purpose of defining a device, a
process or a system in sufficient detail to permit its
physical realization.
• It is an architectural representation, a format, a
guideline represented as symbols, notations, pictorial
forms, that guides us how construct/ develop a
product/process/system most economically, efficiently
and effectively, that reduces the risk of failures.
• Design is the highly creative phase in the software
development where the designer plans how a software
system should be produced in order to make it
functional, reliable and reasonably easy to understand,
modify and maintain.4/11/2020 2

3. • The goal of the design phase is to take the SRS
document as input and to produce the output as a
design document leading to final product.
• System design is the representation of an object
being created.
• A system must be designed in such a way that it
meets the performance requirements.
• The designer’s goal is to produce a model of an
entity that will later be built.
• Software design changes continually.
• Importance of s/w design is stated with a Quality
• Design is the place where quality is fostered in s/w
development
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4. • Design provides us with representations of s/w
that can be assessed for quality.
• Design is the only way that we can accurately
translate requirements into finished s/w product.
• Serves as foundation for s/w engineering and s/w
maintenance steps.
• Without design we risk building an unstable
product – one that will fail when small changes
are made, one that is difficult to test, one whose
quality can not be assessed.
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5. Data
Dictionary
DFD
STD
ERD
CSPEC
PSPEC
DATA DESIGN
ARCHITECTURAL DESIGN
INTERFACE DESIGN
PROCEDURAL
DESIGN
Translating the Analysis Model into a S/W Desgn
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6. Designing the software System
• Data design: transforms the information domain into
data structures. (ERD/DD)
• Architectural Design: defines relationship among major
structural elements of program. It is modular
framework of a computer program derived from
interaction of sub-systems
• Interface design: describes how the software interacts
within itself, to systems that interoperates with it, and
with humans who use it. An interface implies a flow of
information (data/control) (DFD/CFD)
• Procedural design: transforms structural elements of
the program architecture into a procedural description
of software components. (PSPEC,CSPEC,STD)
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7. General tasks involved in design process
• Design the overall system process
• Segment the system into modules
• Design the database
• Specify details of program
• Design input and output
• Design controls of the system
• Document the system design
• System reviews
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8. Design Objectives
• Correct
• Complete
• Reduction of complexities
• Understandable
• Modular construction
• Maintainable
• Risk mitigation
• Optimal utilisation of resources
• Better scheduling
• Meeting the schedules and deadlines
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9. Design Goals
• To rationalise and streamline or simplify processing
• To extend processing capability and flexibility
• To increase productivity by reducing redundant
activities and eliminating unnecessary activities
• To increase management visibility
• Better control over operating processes
• To facilitate managerial planning and analysis of
business activities.
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10. Design Constraints
• Budget
• Time
• Customer
• Attitude of the user
• Technical people / skill
• Standards
• Hardware and software platforms
• Integration with other systems
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11. Design and s/w Quality
• S/W design is assessed with a series of FTR and
walkthroughs.
• McGlaughlin suggests 3 characteristics that serve as a
guide for the evaluation of a good s/w design.
• The design must implement all the explicit
requirements contained in the analysis model, and it
must accommodate all of the implicit requirements
desired by the customer.
• The design must be readable, understandable guide for
those who generate code and for those who test and
subsequently maintain the s/w.
• The design must provide a complete pictures of the
software, addressing the data, functional, and
behavioural domains from implementation perspective4/11/2020 11

12. Technical criteria for good design
• Hierarchical organisation
• Modular construction
• Functional
• Efficient
• Response times
• Flexible
• Portable
• Reliable
• Economical
• Both data and procedural abstractions
• Should lead to modules (subroutines/procedures)
• Should lead to interfaces
• Reduced complexity of connections b/w modules
• Should be derived using a repeatable method
• Secure
• Usable4/11/2020 12

13. Thanks
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