software design and coding conecpts

8/3/2019 Software Design and Coding Conecpts

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What is design? Representation of something that is to be built. Design - > Implementation Example of designs in real life:

Blue print of a building architecture Plan for conducting a workshop Course plan

The process of applying various techniques and principlesfor the purpose of defining a device, a process or a system

in sufficient detail to permit its physical realization In sw engg the goal of the design phase is to transform the

requirements specified in the SRS document in a structurethat is suitable for implementation in some programminglanguage.


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What is design?An iterative process transforming requirements

into a blueprint for constructing the software.


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Design in software engg Process Design

Product Design


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Process design Design for the process of carrying out the design

Methodology selection

Project planning/execution plans Process & documentation standards

Resource allocation charts

Quality and reliability methods


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Product Design Design activities can be braodly classified into two

important parts: Preliminary (or high-level) design AND

Detailed design High-level design: identification of different modules and

the control relationships among them and the definition ofthe interfaces among these modules. Outcome of high-level design is called the program structure or softwarearchitecture.

Detailed design: data structure and the algorithms of thedifferent modules are designed. Outcome of this designstage is usually known as the module-specificationdocument.


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Design Principles The design process should suffer from tunnel vision- i.e., should

consider various alternative approaches based on requirements The design should be traceable to the requirements analysis model The design should not reinvent the wheel Reuse!

Design should be uniform and exhibit integrity- like one persondeveloped the entire system, rules for style & format Design should accommodate change Design should minimize coupling between modules (dependence) Design should accommodate unusual circumstances and should be

structured to degrade gently It should terminate gracefully and not bomb suddenly

Design is not coding, coding is not design Design should have quality assessment during creation, not afterwards

This is to reduce development time Design should be reviewed to minimize on conceptual errors -- Formal

design reviews!


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Product Design

Design of the product to be built


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Data Design The primary activity during data design is to select

logical representation of data objects (data structures)identified during the requirements analysis &

specification phase.Well-designed data can lead to better program

structure and modularity, and reduced proceduralcomplexity.

All data structures and the operations to be performedon each should be identified

A data dictionary should be established and used todefine both data and program design.


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Data Dictionary How analyst, designer and programmer maintain

consistency in naming of data objects?

Where is this data object used?What else will have to change if we modify it?

What will the overall impact of the change be?


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Data Dictionary Is an organized listing of all data elements that are pertinent to

the system, with precise definitions so that both user and systemanalyst will have a common understanding of inputs, outputs,components of stores and intermediate calculations.

Most of the data dictionaries contain following info Name- primary name of the data or control item, the data store, or

an external entity Alias other names used for the first entry Where-used/how used- a listing of the processes that use the data

or control item and how it is used(e.g., input to the process, outputfrom the process, as a store, as an external entity)

Content description- a notation for representing content Supplementary information- other information about data types,

preset values (if known), restrictions or limitations, etc.


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Data Dictionary Once a data object or control item name and aliases

are entered into the data dictionary, consistency innaming can be enforced.

Almost always implemented as part of a CASEstructure analysis and design tools

When a dictionary entry is created, the CASE tool

scans DFDs and CFDs to determine which processesuse the data or control information and how it is used.Therefore, where-used/how-used info is recordedautomatically.


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Data Dictionary-content

description notationNotation Meaning

= Is composed of

+ And

[ | ] Either-or

{ }n n repetitions of

( ) Optional data

* * Delimits comments


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Data dictionary- exampleName Telephone numberAliases None

Where used/how used Get contact Info/ Dial phone

Description Telephone number=[local extension | outside number]

Further refinement of Local extension and outside number:

Telephone number= [local extension | outside number]

Local extension= [500 | 501 ..| 550]

Outside number= [local number | std number]

Local number= any sixdigit string

Std number= 0 + ten digit number


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Architectural design Primary objective is to develop a modular program

structure and present the control relationshipsbetween modules.

software design and coding conecpts

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