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StagesThe guide gives these five as the stages of the software life cycle
Analysis: Data collection, interviews, etc, user requirement, feasibility report
Design: Data structures, algorithms, files. Hardware requirements. Data flow and object model.
Implementation: Also called installation. Direct changeover
Phased introduction
Parallel running
Operation: Detailed planning using GANTT and PERT charts
Maintenance: Bug fixing
But I have also seen these on past exam papers
Validation
Documentation
Analysis: Requirements Specification
Defining what the client wants Inputs: what data/information will
the system require Outputs: what information is
expected from the system Human resources requirements Schedule
Critical success factors. Key objectives.
GANTT and PERT charts
GANTT
List of activities
Order in which they are to be done
Total time required
PERT
Module diagram
Dependencies between modules
Analysis: IPO
Input Processing Output
What data or
information will the system need?
What will the system do to
the data? How will
information be stored and represented?
What information should the
system give its users?
Three stages of programming:
Analysis: Feasibility Report
Feasibility means “Can it be done?”
Brief description of the proposed system
Estimated costs Financial, technical, legal
responsibility Estimated completion date
Analysis: Systems Flowcharting
Tape Storag
e
Disk Storag
e
Document
Process
Input/ Output
Manual Input
Documents
Analysis: Pay System Example
Master FileTransaction
File
Payslips
Calculate Pay
Hours worked
Updated Master
File
(Inputs)
(Processing)
(Outputs)
Analysis: Systems FlowchartPast Paper Answer
Customer orders are collected on paper, keyed in, and stored in a customer orders file. A stock master file is searched to determine whether sufficient stock is available, and a report produced.
The mark scheme awarded one mark for each of the boxes, up to a maximum of five boxes. In my opinion you could have left out the keyboard input, or you could have specified the master file as tape drive (sequential access storage), and you would still get full marks.
Analysis: Review
Why is data collection important? What are the methods of data collection?
What is a requirements specification? What does it contain and what purpose does it serve?
Outline the features of a feasibility report.
Annotate the systems flowchart you created in the past paper exercise. Try to think of another computerised process you could model with a systems flowchart. Discuss with a colleague and prepare the flowchart.
Resources: Computer Science Java Enabled, IB Computing website, Richard Jones’ site (Int. Sch. Toulouse).
Design Stage
Forms (data capture) How the data will get in to the system
Classes, Data structures and Input Files How the data will be represented and stored
Algorithms How the data will be processed
Hardware The components required
Reports, Lists, Output Files What will the output of the system be?
Systems Flowchart Showing the whole system
Other concepts
Modularity: Breaking down the software to make it easier to understand. Can be done in several ways. Classes, input-related, output-related, processing-related.
Prototyping: Quickly building a partially-functioning version of the system with a view to getting constructive feedback from the user to help clarify the requirements.
CASE tools and IDEs: Computer Aided Software Engineering and Integrated Development Environment. Provide useful tools such as debugging, code-highlighting, entity-relationship diagrams, automatic instance variable encapsulation, etc.
Testing
Imagine you have a textbox that should only accept values from 0-100.
Normal data: Data that the system should expect, ie that is well within the normal range. Eg 23, 56, 89, etc
Extreme data: Data at the boundaries of what is acceptable, eg -1, 0, 1, 99, 100, 101
Abnormal data: Data that is outside the normal range of expected data and which perhaps should produce an error, eg -34, 155.
Also be familiar with tracing algorithms, debugging
White-box testing: Testing done by the programmer, focusing on an understanding of how the program should function
Black-box testing: Testing done by the user, focusing on an understanding of what the program should achieve, but not how it should achieve it.
Implementation Parallel running:
Keep the old system and the new system running at the same time. Adv: No disruption to business because even if new system doesn’t work, old system is still available. Disadv: Twice as much work required to keep both systems running.
Phased introduction: Bring the new system in gradually, replacing the old system function by function.
Adv: Can be the best of both worlds between Parallell Running and Direct Changeover. Disadv: Not often possible to replace a system bit by bit.
Direct changeover (big bang): “Flicking the switch” between old system and new system. Adv: Avoids extra
overhead of having two systems running in parallel. Disadv: Disruption to the business if the new system doesn’t work properly.
Things to consider: Bugs in the new system
Cost of running two systems in parallel
Training new users
Interruption to business
Operation and Maintenance
Constant review
Performance evaluation
Bug-fixing
Feeds back into the Analysis stage to create a cycle
Documentation Two types:
System documentation: Intended for programmers so they can maintain the system. Lists and descriptions of modules, classes, variables, data structures, hardware requirements, etc.
User documentation: Intended for users of the system so they can operate it usefully. Illustrated instructions, how to install, how to operate, etc.
Master File vs Transaction File
Master File Permanent
Complete set of records
Transaction File Temporary
Contains only those records that have been changed recently
Used to update the master file
Batch vs Online vs Real-TimeBatch Processing
A large amount of input happens over time and then then whole set of input is processed in one go
Examples: Any monthly billing, eg internet billing (you access the internet lots of times over the course of a month, then at the end of the month your ISP totals your usage and gives you the bill)
Online Processing (also known as interactive processing)
Input is processed (almost) immediately
Example: Flight booking system. As soon as you book the seat it is yours. Can you explain why flight bookings could not be processed in batches?
Real-Time Processing
Input is processed immediately and continuously
There is generally no user
Input comes from sensors
Examples: Auto-pilot. Large volume of data harvested from multiple sensors continuously. System reacts in real time.
Validation vs Verification
Validation
A validation check just checks if input is possible, appropriate or reasonable
Keppler accidentally enters 81 for his age, instead of 18
This is valid because he could be 81
Validation check does not check if it's actually true
Examples are range check (eg is aged entered between 0 and 100) and type check (eg has the user entered a number rather than a string)
Verification
The process of checking if data is true, factually correct
Two ways of doing it:
Visual checking, ie proofreading
Double-entry of data, ie inputting the whole data set again and checking if both sets are the same
Social Effects of Computer Systems
Positive More leisure time for people because computers do their work
Online commerce reduces the need for travel
Communication more immediate
More accessibility for elderly or disabled people
Computers can do dangerous/repetitive jobs
Labour-saving devices eg washing machines, security systems, etc
Negative Training required
Purchase of a computer sometimes required (cost)
Unemployment in areas where computers do work, eg factories
Longer hours worked by people always contactable eg email, mobile phone
Some health issues, eg eye-strain, back problems, RSI (repetitive strain injury)