Implementation

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Software Implementation– transforming design into code

Requirements Analysis

Software Design

Implementation

TestingDeploymentEvolution

Systems Engineering

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Implementation Approaches

Big bang Code entire system and test in an

unstructured manner Top-down

Start by implementing modules on top of hierarchy and test by coding stubs

Bottom-up Start by implementing modules on bottom

of hierarchy and code drivers to test Feature-driven

Implement and test a minimal set of modules implementing a function

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Implementation ApproachesAdvantages and Disadvantages

Big bang advantages None

Big bang disadvantages Difficult to debug Much throwaway

code Critical and

peripheral modules not distinguished

User does not see product until very late in the development cycle

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Implementation ApproachesAdvantages and Disadvantages

Top-down advantages

Separately debugged modules

System test by integrating previously debugged modules

Stubs are easier to code than drivers

User interfaces are top-level modules

Top-down disadvantages

Stubs must be written Low-level, critical

modules built last Testing upper-level

modules is difficult

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Implementation ApproachesAdvantages and Disadvantages

Bottom-up advantages Separately

debugged modules

System test by integrating previously debugged modules

Testing upper-level modules is easier

Bottom-up disadvantages Drivers must be

written Upper-level,

critical modules are built last

Drivers are more difficult to write than stubs

User interfaces are top-level modules

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Implementation Plan

Specifies which implementation strategy will be employed

Divides the project into phases Specifies a schedule for each phase

including the following steps for each phase: Coding Unit testing Integration of units Integration testing

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Sample Implementation PlanSchedule

Week number 4 5 6 7 8

Activity

Phase I codingPhase I unit testingPhase I integrationPhase I integration testingPhase II codingPhase II unit testingPhase II integrationPhase II integration testing

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Programming Standards

Most organization insist that their code conform to style, format and content standards.

Coding standards help organizations in several ways: Codes and associated documentation are clear to everyone. Standards and procedures help the organization of thoughts and

avoid mistakes. Individuals can leave and return to their work without losing

track of what they were doing. Standardized documentation helps in locating faults and making

changes. Standardized documentation clarifies which section of your

program perform which functions. Standards and procedures help in translating designs to code,

and make changes in design easier to implement in the code.9

Programming Standards

“A most critical standard is the need for a direct correspondence between the design components and the code components. This correspondence should occur in such areas as modularity, coupling, cohesion, etc. Without this correspondence testing, maintenance and configuration management become impossible.”

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Why Programming Standards?

The need to return to the code later to correct a problem, integrate a new feature, or tune for performance.

It should be possible to determine what you are doing without reading the code line by line. waste resources?, misinterpret the original

intent?, introduce errors? A well documented program will be easier

to modify, debug, and maintain. 11

Programming Standards

Areas where standards are usually applied

End-user documentation Application design documentation Source code

Layout & Style Classes/modules Methods/procedures Coding for Efficiency

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Programming Standards End-user Documentation

“There's nothing more frustrating for a user than to be sitting in front of an application and not know how to accomplish a task that the application is capable of doing.”

Provide online help Provide user manuals Provide Developers manual?

write the documentation at the level of understanding of the people who will use the software.

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Programming Standards

Application Documentation Give the application a name. State the goal of the application. Describe the features/packages of the application.

Provide a list of the features the application will support and how the features will be integrated into the final product.

Develop an implementation strategy.Break down the major components of the application design, describing how each will be implemented into the application and integrated with the other components.

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Layout & Style

Programmers should strive for simple and readable code

Shorter code is usually simpler code

Simpler code typically contains fewer decisions

Excessively nested logic should be avoided

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Layout & Style

Indent properly.Indent all the code within methods, indent all conditionals and loops, etc.

Use white space liberally. Use inline comments liberally. Code should be simple and easy

to read16

Comments and Internal Documentation

Most successful software systems exist for several years and require modification during that time

Comments are the chief source of information about the source code, and thus are extremely important

A header comment block summarizes the purpose of a module (class or method)

Line comments are inserted into the source code to explain the objectives of a subset of the instructions comprising a module

to describe data declarations and blocks of code where the purpose of a statement is not entirely

obvious Each major control structure (loop, selection) should

be clarified through a line comment17

Comment Blocks Place a header comment block at

the top of each method/module. what the method is called who wrote it where it fits in the general system when the method was written and revised why the method exists how it uses its data structures and

algorithms. Expected input and possible output Expected extensions or revisions

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Programming Standards Modularization Rules:

Each method must perform only one task Global variables should be used with care. Data should

be shared through the parameter list If, during implementation, a need arises for a class not

specified in the design, the design must be reexamined before the new class is implemented

Separate data management from the user interface. Write separate procedures to manage data and call them from the

user interface code. Give each module a clear, simple name that indicates

what it does.

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Programming Standards

Declarations: All variables must be declared and explicit types

used Name of variables and methods should describe

their content or usage. An exception can be made for naming subscripts and counters

Declarations of any files should precede variable declarations

Declarations of instance variables in a class should precede method definitions

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Programming Standards

Naming Conventions: Name of variables and methods should describe

their content or usage. E.g. a variable that represents the total number of

employees EmployeeTotal or EmployeeCount Is much better than n.

Use abbreviations consistently. "Tm", for example, is only two characters shorter than

"Time" and much less readable. Use common tags but be consistent

Num for Number, Idx for Index, … Don't use Num some of the time and Number or Count at other

times. 21

Programming Standards

Naming Conventions: Make the name readable.

A good rule to apply here is that you should be able to read your code to someone over the phone and have them be able to write it down without asking you for spellings.

Use a noun for variables - a word that represents the data.

Use a noun and a verb for procedures. E.g. "AddContact" for a procedure that adds a new

contact to a database.

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Programming Standards

User interface: Put control in the hands of the users.

provides features so users can customize their environment.

design interface to have the look, feel, and functionality of the applications with which users are already using.

Integrate your application with the operating system.

associating file types with your application supporting drag and drop where applicable supporting mail features, etc.

Apply the quality function deployment paradigm23

Quality function deployment

Goal Maximize user satisfaction

Needs of user software requirements Requirements

Normal requirements Expected requirements Exciting requirements

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Performance & Perception

True Performance This is the actual speed at which the

code is executing Perceived Performance

This is the performance as perceived by the user.

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Performance

Two basic ways to increase the perceived performance of an application: Distract the user during long processes.

Splash screens, pretty pictures, and progress meters are common tools used to give users something to look at while a long running process is taking place.

Give users something else to do during long processes.

When possible, you should try to move time consuming tasks into a background process and allow the user to continue with something else while the process is running.

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Examples of Coding Standards

Examples of Java coding standards may be found Here

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Summary

Understand the problem before you begin building the solution.

Follow accepted standards for code/user interface design.

Write code that is readable. Separate user interface and data management. Design for the most efficient use of the program by the

user. Design code that can be re-used. Keep the program simple Localize input and output

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The End

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______________________Devon M. Simmonds

Computer Science Department

University of North Carolina Wilmington____________________________________________ _________________

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