Software Engineering

A little while ago a friend asked me what kind of programming I was interested in. I ended up explaining the difference between system programming and application programming: In application programming programmers build applications. Application programs include websites, video games, iPhone applications, Microsoft Word, Microsoft Excel, Web browsers and other programs that people use for entertainment, communications, accessing information, organizing, and getting work done. Application software interacts with people or users. Systems programming is creating technology that programmers use to build applications. In order for an applications programmer to build an application, he needs an operating system, a programming language, and other tools to get the application built, tested, and working. System programming includes creating and working on: operating systems database systems programming languages software libraries software that controls hardware very directly Software exists in layers. Application software runs on top of and interacts with system software. System software runs on top of and interacts with the physical hardware. Another way of looking at it: People make application software do work. Application software makes system software do work. System software makes the physical machine do work. TAKEN FROM HERE:http://nickmudge.info/?post=107
System programming is done for supporting or for executing another program.ie, OS , here the programming is done for supporting or executing another programs.

For eg: OS it make user friendly because of the execution of 1000 or more program inside that we cant see.

Programming language are use to program or mold for any particular task.For eg: wordprocessing software like MS word etc

1)whenever we are developing a small application we go for waterfall model.

2)when we have a short term project.

3)when we are sure that the requirement never changes.

These are the stages in which we adopt the waterfall model.

When we talk about the phases we talk about the steps compiler should do in order to finish it job. For example phases could be creating local variables symbol table, generating parsing tree, lexical checking, optimization, etc.

When we talk about passes we talk about times some operation was repeated. For example there are 2-passes Assembler compilers. It means that before giving the results it repeats some steps twice, most of time times optimization step. The more passes you put the better quality result you get. The same applies to music and video encoding.

For example:

Source code:

i++;

i++;

i++;

1st step (pass):

i = i + 1;

i = i + 1;

i = i + 1;

2nd step (pass):

i = i + 3;

Most of compiler before generating results converts source code some kind inner language that is easier to parse, check in later steps.

As you can see two-pass compiler would generate better quality code, than one-pass compiler, but the first one would be faster to compile.

Design is a creative process that occurs in many settings. The steps outlined below offer a structured format for a formal design process based on models from industry.

Analyze the situation

Before beginning the design, sort out what problem you are trying to address.

Write a brief

Write a short statement giving the general outline of the problem to be solved.

Research the problem

Sometimes a problem can be solved "straight out of your head," but in most cases you will need to gain some new information and knowledge.

Write a specification

This detailed description of the problem spells out what the design must achieve and what limitations will affect the final solution.

Work out possible solutions

Combine your ideas with information obtained from your research to suggest several possible design solutions. Sketch several possibilities on paper.

Select a preferred solution

Decide which solution to develop. Although the chosen solution should, ideally, be the one that best satisfies the specifications, other constraints such as time, cost, or skills may limit the decision.

Prepare working drawings and plan ahead

Draw the chosen design including all the details that are important to its construction.

Construct a prototype

Make the product. In industry a model is usually built first and the final product is developed from it, but in most classrooms, the model is the final product.

Test and evaluate the design

Testing is ongoing as the construction progresses, but a final test of the entire system or model proves if the project does the job for which it is designed. Look back at the specifications and check the requirements carefully. Ask such questions as: How well does the design function? Does the design look good? Is the product safe to use? Were suitable materials used? How could I have improved on my design?

Write a report

The report provides evidence of your work in analysis, planning, designing, carrying out the practical work, evaluating, and communicating.

Sales Job: "The money."

HR Job: "I like helping people."

Teaching Job: "I want to give others the same sort of education I had"

Mechanic Job: "I like cars."

Summary: There are as many answers as there are jobs and the answer is always glib and obvious.

A process model for software engineering is chosen based on the nature of the project and application the methods and tools to be used and the controls and deliverables that are required.

All software development can be characterized as a problem solving loop in which four distinct stage are encountered, these are status quo, problem definition, technical development, and solution integration, status quo represents the current state of affairs, problem definition identifies the specific problem to be solved, technical development solves the problem through the application of some technology, and solution integration delivers the result to those who requested the solution in the first place.

Technical development

Status quo

Solution integration

Problem definition

Figure: The phases of a problem solving loop

There are several models used in S.E these are –

i. The linear sequential model.

ii. The prototype model.

iii. The RAD model.

iv. The increment model.

v. The spiral model.

vi. The win win spiral model

vii. The concurrent development model

viii. The component based development model

#The linear sequential model/waterfall model-

The LSM sometime called the classic lifecycle or the waterfall model. This model suggests a systematic sequential approach to software development that designs at the system level and progress through analysis, design, coding, testing and support. The LSM encompasses the following activities-

System /information engineering and modeling .Because software is always part of a larger system the work begins by establishing requirements for all system elements and then allocating some subset of these requirements to software. This system view is essential when software must interact with other elements such as hardware, people and database. System engineering and the analysis encompass requirements gathering at the system level with a small amount of top level design and analysis. Information engineering encompasses requirements gathering at the strategic business level and the business area level.

i.Software requirements analysis-

The requirements gathering process is intensified and focused specially on software. To understand the nature of the problem to be built, the software engineering must understood the information domain for the software as well as required function. Behavior, performance and interface requirements for both the system and the software are documented and received with the customer.

ii.Design-

Software design is actually a multistep process that focuses on four distinct attributes of a program. Data structures, software architecture, interface representation and procedural detail the design process translates requirements into a design which documented and becomes part of the software configuration.

iii.Code generation-

The design must be translated into a machine readable form. The code generation steps perform this task. If design is performed in a detailed manner code generation can be accomplished automatically.

iv.Testing-

Once code has been generated, program begins. The testing process focuses on the logical internals of the software, ensuring that all function externals that is conducting tests to uncover errors and ensure that defined input will produce actual result that agree with required results.

v. Support-

System/information engineering

Analysis

Design

Code

Test
Software will undoubtedly undergo change often it is delivered to the customer change will occur because errors have been encountered because the software must be adapted to accommodate change in its external environment or because the customer requires functional or performance enhancements. Software support maintenance reapplied each of the proceeding phases to an existing program rather than a new one.