This document discusses software design principles and activities. It notes that requirements analysis should minimize design assumptions while ensuring consistency with technology. Analysis and design are interwoven. Design models refine analysis models with more implementation details. Design engineering starts with data/class design and includes architectural, interface, and component level design. The design must implement requirements and accommodate implicit needs while being understandable. A good design exhibits recognizable architecture and patterns, modularity, and distinct data, architecture, interface and component representations.

1. BY
M.LAVANYA,M.SC(CS)
NADAR SARASWATHI COLLEGE
OF ARTS AND SCIENCE ,THENI.

2. Dilemma:
 requirements analysis should make minimal
assumptions about the system design.
 But the requirements definition must be
consistent with computing technology and the
resource available.
 In practice analysis and design are
interwoven. However, do not to allow the
analysis tools to prejudge the system
design.

3.  The elements of the design model use many
of the same UML and SSAD diagrams that
were used in the analysis model.
 The difference is that these diagrams are
refined and elaborated as part of design;
more implementation specific detail is
provided.

4.  Data / class design
 Architectural design
 Interface design
 Component level design
 Design engineering starts with DATA / CLASS
DESIGN- the foundation for all other
elements of the design

5.  Transforms analysis – class models into design
class realizations and the requisite data
structures required to implement the
software.
 The classes and relationships defined by CRC
cards and the detailed data content depicted
by class attributes and other notation
provide the basis for the data design activity.

6.  Part of class design may occur in conjunction
with the design of software architecture.
 More detailed class design occurs as each
software component is designed.

7.  Defines the relationship between the major
structural elements of the software the
architectural styles and design patterns.
 The architectural design representation – the
framework of a computer based system – can
be derived from the class based elements
and the flow –oriented elements.

8.  Describes how the software communicates
with systems that interoperate with it , and
with humans who use it.
 Usage scenarios and behavioural models
provide much of the information required for
interface design.

9.  The component-level design transforms
structural elements of the software
architecture into a procedural description of
software components.
 Information obtained from the class –
models, flow models and behavioral models
serve as the basis for component design.

10.  The design must implement all of 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 a readable ,
understandable guide for those who generate
code and for those who test and
subsequently support the software.

11.  A design should exhibit an architecture that
(1) has been created using recognizable
architectural styles or patterns , (2) is
composed of components that exhibit good
design characteristics and (3) can be
implemented in an evolutionary fashion.
 for smaller systems , design can sometimes be
developed linearly.

12.  A design should be modular ; that is , the
software should be logically partitioned into
elements or subsystems.
 A design should contain distinct
representations of data, architecture ,
interfaces and components.
 A design should lead to data structures that
are appropriate for the classes to be
implemented and are drawn from
recognizable data patterns.

13.  Abstraction – data , procedure , control.
 Architecture – the overall structure of the
software.
 Patterns – “conveys the essence “ of a proven
design solution.
 Modularity – compartmentalization of data
and function.
 Information hiding – single- minded function
and low coupling.

14.  Refinement – elaboration of detail for all
abstractions.
 Refactoring – a reorganization technique that
simplifies the design.