1. Visual Basic: An Object Oriented Approach
1 – The Software Life-Cycle

2. Introduction to Software
Software is…
the combination of instructions and data a computer system uses to perform tasks
complex in structure and detail
difficult to construct
can involve the development of many inter-related components
Software development needs a plan!

3. Software Structure A software system involves information (data)
processes (operations)
an organisational structure (some way of relating the operations and the data they must work on)
Large-scale structure

4. Objects Even in small software systems..
a lot of data
many different types of operation
very complex interactions between them
Objects combine items of data with the operations that work on them including links to other objects

5. Visual Basic Objects
Visual Basic can be used to create Object-Oriented Programs
Facilities to create…
New types of object
Forms (user-interfaces – a specific type of object)
Models of systems in which objects interact with each other
Object Interactions

6. Developing Software
Scale is important. Consider the differences between building…
A small garden wall
A house
A multi-storey building
The scale of a project should dictate the amount of analysis, planning and design work performed on it.

7. The Software Life-Cycle
The software development process takes place over a number of phases…
Find out what is required
Design a suitable solution to the requirements
Build a system to the design
Test to make sure it works as designed
Work with the system, changing it to meet changing requirements and repairing faults as they emerge
Different software developers approach these phases in different ways.

8. Factors that affect the form of the software life-cycle…
the size of the project
the number of developers
the size of the company that employs the developers
the level of formality applied to development
the developers’ expertise and experience
the customers’ experience of software deployment

9. Waterfall life-cycle Features… Advance planning of whole process
Fully planned allocation of resources
Rework can affect one or all phases
Very late emergence of any working software

10. Evolutionary Prototyping life-cycle
Features…
Suits small projects and small teams
Early feedback to customer
Unknown project completion date
Customer can cause project to drag on (possibility of feature creep)

11. Object-Orientation in the life-cycle
The decision to develop an object-oriented solution affects the whole process…
Requirements Analysis: identify objects
Design: describe objects in terms of their attributes and capabilities
Implementation: create objects as designed
Test objects in isolation and to ensure they interact properly
Upgrade objects and introduce new object and interactions during software use phase.

12. Software Requirements Specification
State what the software is to do
Start with a clear description
Decompose into individual requirements
The software should maintain a list of names and contact telephone numbers.
Add names and numbers to a list
Remove entries from the list
Retrieve a number given an name
Generate a printout of the list on a printer

13. Requirements Specification II
Add names and numbers to a list
Remove entries from the list
Retrieve a number given an name
Generate a printout of the list on a printer
Identify objects (nouns) in the requirements
Convert plurals to singular
Remove from the list…
duplicates
synonyms
incidental nouns that refer to objects with no responsibilities
vague or non-specific items (e.g. ‘details’, ‘information’)
nouns that describe simple attributes (colour, height)
objects that might be responsibilties e.g. PrintOut (vagueness of language has confused a noun with a verb)
Name (attribute of Entry)
Number (attribute of Entry)
List
Entry
Printout (responsibility of List)
Printer

14. Requirements Specification III
Assign responsibilities to the objects in the remaining list
Each object should be responsible for something action or operation (or it is probably not an object)
In some cases, a responsibility may not be until you consider the requirements of similar things in other programs. E.g an Entry does not just appear on a screen or printout – it must be made responsible for this
List Add entry, Remove entry,
Find entry, PrintOut
Entry Display, Print
Printer PrintText

15. Algorithms
An algorithm is the step-by-step description of an operation
May involve repeating some steps
May involve deciding whether to include some optional steps
An algorithm is commonly devised by task-decomposition (top-down decomposition)…
Take a task and break it into a two or more sub-tasks
Break each sub-task down and repeat until each individual step is tractable
…or sub-task synthesis (bottom-up composition)…
Combine incremental operations that you know how to do to form bigger operations

16. Objects and Algorithms
Objects have capabilities
Either…
we have designed them for a specific task (top-down decomposition)
…or…
they already exist and we will make use of their capabilities in a new task (bottom-up composition)
Either way, we can implement an algorithm by creating collaborations between objects
:List
[for all entries in list]: print
:Entry
:print
:Printer

17. Summary
Software development is complex and needs careful planning – a life-cycle approach is often used
Software is a combination of information (data) and operations (instructions)
The way that these are combined is the structure of the software
Objects are used to create smaller structures that can collaborate on a major task
In object-oriented design, we need to…
Identify the objects needed to do the task
Appoint these objects with responsibilities
Orchestrate the objects to collaborate on the overall task