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Principals of Software Design and Development

Introduction to Programming Languages

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Learning Objectives

Revisit prior learning Describe the factors that influence the

programming languages. Select an appropriate language for a

given scenario Justify the choice of language

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Quick Quiz

Write down all the objects you can think of that we use in Visual Basic

Now write down properties that can be changed on these objects

Describe what an event is? Now give events that can be attached to these

objects Why do we use naming conventions Give naming conventions for a label, a text box, a

form and a command button CW-V1 SDD 020 3

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Types of Programming Language

Procedural Object-Oriented Visual – event driven

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Factors that influence programming languages

If you were going to choose a programming language to develop software for a large company what would you think about before you bought it?

organisational policy; development and maintenance costs; Ease of use The Interface – features and tools it offers Reliability Expandability Availability of trained staff to use or teach others

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Organisational Policy

Some organisations have an organisational policy as to which hardware and software is to be used.

Eg may choose Microsoft as very large company and need this level of support

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Development and Maintenance costs

When embarking on a project some organisations will look at costs.

Some languages have a reputation for cutting maintenance time where others don’t!

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Procedural Factors

Ease of Use

Easy to create small programs but larger ones become very complex. Large bank of commands and syntax has to be learnt.

Interface All instructions must be typed directly into an editor. Basic help files may be available.

Reliability Simple programs run reliably, but become less so as more procedures are added

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Procedural Factors

Expandability Adding on extra routines quickly leads to messy, unreliable and hard-to-read code

Training Requirement

The editing environment is very simple and easy to learn – may just be a text editor. However a lot of specialist knowledge in needed as debugging tools and help files will often be very basic and ‘unfriendly’. This can make training from each new language a long, expensive process.CW-V1 SDD 020

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Object Oriented FactorsEase of Use

Can make creating large, complex applications easier as objects, once coded, can be used multiple times in slightly different ways. However the languages themselves and the concepts involved tend to be very complex and difficult to learn. Very difficult to track errors as objects can be closely related.

Interface Usually a text editor. Later versions of languages have visual prompts, debugging tools and help files which can make the programmer’s life easier

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Object Oriented Factors

Reliability Programs are usually very reliable as multi-use objects will have been thoroughly tested.

Expandability Designed for this purpose. Extra objects can be added at any time. Objects can be changed once and will all share the changes

Training Requirement

Intensive, specialist training needed to begin with but little needed once the concepts have been learnt

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Visual(event driven) factors

Ease of Use

Designed to be easy to pick up. Becomes progressively more difficult as used for more complex programs.

Interface Standard Windows controls (e.g. option button, drop-down list) can be placed on a screen. Code is added using a user friendly editor that suggests actions that can be taken with the control and useful key command words. Help files are usually detailed and involve examples.

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Visual(event driven) factors

Reliability Variable, depending on programmer skill. Mixture of procedural and OO concepts can make code messy and difficult to follow / structure.

Expandability Becomes less reliable and harder to manage as more functionality is added although large programs can be created if initially designed that way.

Training Requirement

Minimal – designed as a non-expert programming tool.

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Activity

Read the scenario Select the type of programming language you think is best Open SDD021 and fill in the headings Justify why you have chosen it in terms of: organisational policy; development and maintenance costs; Ease of use The Interface – features and tools it offers Reliability Expandability Availability of trained staff to use or teach others

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What do you have to do now?

Task 1 presentation – now add slides on the following using today's presentation and your scenario notes SDD 021

Describe the factors influencing the choice of 3 types of languages. One of these must be a visual language. Give your reasons for the choice of language (P2)

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