sd revision
DESCRIPTION
Software DevelopmentTRANSCRIPT
Personnel Lifecycle
Languages
HLL constructs& Algorithms
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topic
Documentation
Characteristics
PersonnelPersonnel
Project Manager The head of the development team, this person will direct and monitor all aspects (personnel, time-scales, budget) of the project from start to finish
Client The company or organisation who want a new system
Systems Analyst Has the task of gaining an understanding of the client's needs and conveying these to the developer or team of developers. Outlines the basic problem in a problem specification. Discovers exactly what the client wants in the solution.
The Systems Analyst uses three main methods to find out about what the client wants and how to get them what they want:Experience (of all stages of software development, technical knowledge and working within time/money/technical restrictions)Analytical Observation & Problem solving (observing current system functions and how and documents are used)Communication (with the Clients staff and with the project manager)Programmers Implement the solution
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DocumentationDocumentation
specifies what the new system has to be capable of doingRequirements Specification(Operational Requirements)
states the desired system, setting out hardware and software specifications plus any human and organisational implications.
System Specification
Provides a snap-shot of the development and suggests possible options for solutions
Feasibility Study
A plan to solve the problem, shows functionality of system
System Design
A formatted printout of program code with indentation of loops and conditions
Structured Listing of Code
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The Software Development Lifecycle
Analysis
Testing
Documentation
Design
Evaluation
Implementation
Maintenance
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AnalysisAnalysis
Analysis is the process of finding out what the client wants and needs and looking at the existing system to find out what the new system needs to do.
Systems Analysts can use CASE tools to help them with the analysis phase (and other parts of the software development process)
CASE stands for Computer Aided Software Engineering
CASE tools can be used to:
* assist the summarising of a project's initial requirements.
* allow graphical representation of modules within a project tree structure allowing individual modules within a project, to be selected and worked on.
* facilities to have program code generated from the design which in turn has been generated from the specification.
* graphical design representation editing.
* code editing.
* documentation generation which tends to be in Rich Text Format (RTF) allowing data export to most word processing packages.
* work on networks, different languages and OS
Lifecycle
DesignDesign
This is where a plan for the new system is drawn up.
The HCI should be designed
A variable table be be created to specify any variables required
A structure diagram is a graphical approach to designing the main steps of the solution
Pseudocode is a textual approach to designing the main steps
An indication of Data Flow in the design.
A set of Test Data should be created to test the design at this stage. This will check for errors in the design such as logical errors
Lifecycle
ImplementationImplementation
Implementation means taking the design template and converting it into a form the computer can understand – code.
Things to consider:
Data StructuresThe correct types should/must be implemented.
Modular Code should be written which defines the subprograms. Coupling of existing subprograms that have been stored for use within other
programs e.g subprograms which search or sort a list of numbers, to save time and to improve speed and efficiency in development
Variable and Subprograms & functions and variable names should be clear, sensible subprogram names and meaningful.
Internal Internal commentary has no effect, but helps when maintenance Commentary activities take place.
Loop usage Make sure execution of these is carefully considered, and the proper 'escape' condition has been applied
Logic Tests Make sure execution of these is carefully considered, and the logical test has been applied correctly
Lifecycle
TestingTesting
There are different ways that software should be tested.
*** A Dry Run is the process of going through the program in your head and keeping a note of the different values of variables on paper.
This is used to try and eliminate many errors before your run the program.
Many programs have a built in ‘trace’ facility which will do this for you.
*** A specially designed set of test data is used to test your program when it runs.
This test data should include:* A set of normal, valid data to check for proper operation.* Test at the limits (extremes) to see if boundary conditions function as
expected.* ‘Exceptional’ data to see how the software will react to unexpected data
input.Alpha testing is the first stage of whole program testing and takes place with the developers.Beta testing (acceptance testing) is the second stage and often takes place within the company, under actual conditions
If programs are made up of different modules, the modules are tested separately then are tested again when they are integrated into the main program.
Lifecycle
DocumentationDocumentation
User Guide
Technical Guide
It tells the user how to successfully use the software and tends to be, as far as possible, in non-technical language
• Clear instructions on getting started: how to install the software onto hard disc and start the application.
• Backup procedures for the original disc(s) (if required)
• Structured novice tutorials: step by step information about what the user will see and how to respond when the software is running.
• Experienced users will be provided with a summary/quick reference guide.
• Screen dumps and an indication of how the user should interact with the software
• Step by step guide to software installation
• Hardware and Software requirements
• Storage requirements
• Common problems and how to solve then
• Registration/Support (Ph. No.) Details
• FAQ/Any other relevant information
provide information on aspects of the software and hardware requirements
* Both these documents can be supplied in a README or help file.*Lifecycle
EvaluationEvaluation
• How well have you understood the Client's problem?
• How well does the design reflect the Analyst's system specification?
• Does the program match the design and consequently solve the customers problem? Is it maintainable?
• Are there limits of the software reliability/robustness?
• What improvements that could be made to the visual appeal, screen layout, prompts for user, etc given time?
The evaluation stage allows you to compare what you have done with what you were asked to do. There are several questions which should be asked about different stages in the development process;
Lifecycle
MaintenanceMaintenance
Corrective Maintenance Eradicating errors reported by the Client, which were undetected at testing.
Adaptive Maintenance Altering the software to 'interface' with changes in the operating environment (new
hardware/software).Perfective Maintenance This is the largest of the four, allowing enhancements to the performance of the system in some way.Preventative Maintenance Improving the future maintainability of a development
There are four types of maintenance activity:
Lifecycle
CharacteristicsCharacteristics
A program is ROBUST if it can cope with problems that come from outside and are not of its own making. For example unexpected data entered by a user or an unexpected condition such as a printer jam.
RELIABILITY is an internal matter. A program is reliable if it runs well, and is never brought to a halt by a design flaw. A reliable program should be able to inform the user if an error occurs, try to recover from the error and if all else fails stop running with a minimum of fuss.
A program which is said to be PORTABLE is machine independent, it should run on most computer systems using different hardware and operating systems.
A program is said to be MODULAR if it is clearly divided into sub-programs or modules which each perform a specific task.
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LanguagesLanguages
Before you begin to implement a solution to a problem you must consider what type of programming language is most appropriate for the task.
There are four different types of programming language.
Procedural Declarative
Event-Driven Scripting
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ProceduralProcedural
A program written in a Procedural (Imperative) language will have a main program from which subprograms such as procedures/subroutines and/or functions will be called, i.e. the control of the flow of execution lies in the code in the main program.When choosing a procedural language to solve a problem, the best solution will be obtained when the particular features of the procedural language are most closely matched with the particular features of the problem to be solved. i.e. matching the objects and operations of the language to that of the problem
Common features of a Procedural language:
Data A range of data types and data structures can be used.
Calculation Arithmetic and logical operations are possible.
Sequencing The flow of control from one instruction to the next.
Control Repetition of instructions. (a fixed number of times or condition Structures controlled)
Conditional Which test some criteria and may transfer control elsewhere in the Structures program.
Modular Procedures or subroutines, which let you break a program into smaller Structures named sections.
Parameter Data flow into and out of the procedures/subroutines.Passing
Languages
A declarative language stores a list of facts and rules relating to these facts, in what is known as a knowledge base. When the user enters a query, the declarative language attempts to find a solution by searching the knowledge base. Because of their usefulness in resolving logical issues, much research in declarative language usage is being done in the sphere of Artificial Intelligence, where the intention is to develop machines which can make logical decisions in a natural way.
A declarative has a list of facts (things that are TRUE) in what is known as a knowledge base.
DeclarativeDeclarative
Declaration of Fact Interpretation
is_daughter(mary, susan) Mary is Susan's daughteris_daughter(susan, julia) Susan is Julia's daughteris_daughter(claire, alison) Claire is Alison's daughter
Query Result
is_daughter(claire, alison)? which will return the answer TRUE or YES because an exact match can be found in the database. is_daughter(tom, alison)? will return FALSE or NO as there is no match in the database.
These facts can be interrogated by a query.
Languages
An Event-Driven Language also uses a procedural approach, except that the procedures are associated with objects available within the application. Execution of a procedure is triggered by an EVENT (input from the user) involving an OBJECT, e.g. the click of a button on a form or the selection from a menu.
Event-DrivenEvent-Driven
Typical Objects Typical Events When to execute code
Command Button Click Mouse click on objectRadio Button Double-Click Mouse double-click on objectToggle Button Got Focus Cursor over objectList Box Lost Focus Cursor moved from objectMessage Box Key Down Mouse button pressed but not releasedDialogue Box Key Up Mouse button releasedText Box On Enter Application, Form, Dialogue Box openedImage Box On Exit Application, Form, Dialogue Box closed
Languages
ScriptingScripting
A scripting language is one which is designed to be used in a particular operating or application environment. They tend to be an additional facility available in several applications packages, particularly database management packages.The benefits of using a scripting language are that it increases the flexibility of a programming language, allowing it to be customised to meet the users needs. Features that may not be readily available in a package can be added using scripts - e.g. a set of commands or actions can be carried out with a single key press (similar to a macro)
Languages
High Level Language Constructs & High Level Language Constructs & AlgorithmsAlgorithms
ModuleLibraries
Data Types
Linear Search
CountOccurrence
Maximum &Minimum
Parameters
Variables Menu
Module LibrariesModule Libraries
Module Libraries are pre-written and tested routines that the programmer can CALL upon to support and speed up the development process.
Most software companies will build up or buy in module libraries of regularly used modules of code, often in a variety of languages. These library modules would be tried and tested, robust code.
Comprehensive libraries of these modules can almost lead to the "cut and paste" method of software development. This approach requires very little new code to be written and the software consists almost entirely of library modules, customised for the task and linked together in the required logical order.
HLL page
Data TypesData Types
Simple Data Types
Type Description Sample Data
String text & numbers Hello, 95 Clifton Road
Integer whole numbers 12, 267, 2300
Single real numbers 2.99, 13.725, 15.01
Boolean true or false True, False (or Yes, No)
Complex Data Types
An Array is a set of information that is related. You set how many data item you want the array to store.
DIM Name(10) of String this is an array which can hold 10 names
HLL page
VariablesVariables
There are two different ways variables can be used:
Global Variables
Global Variables are declared at the beginning of your program and can be used and changed throughout the whole program. They may be used in different sub-programs and can be passed as parameters.
Local variables
Local Variables are declared within ONE sub program and can the data only be used and changed within that one sub program. Local variables cannot be passed as parameters.
It is good programming practise to try and have as many local variables and as few Global variables as possible.
HLL page
ParametersParameters
Parameters handle the flow of data within your program. A parameter can be either a variable or a value. Parameters can be passed into and out of a sub-program.
There are two different ways to pass parameters between sub-programs.
You can pass parameters by VALUE or you can pass parameters by REFERENCE
By Value
Parameter Passing by VALUE is when a value is passed into a subprogram for use by the subprogram, but the changed value is not passed out.
Parameters passed by Value are indicated by putting brackets around the parameter name.
By Reference
Parameter Passing by REFERENCE is when a value is passed into a subprogram for use by the subprogram, and then the changed value is passed out to be used by other sub-programs.
Parameters are passed by Reference by default and are simply listed in the parameter list. HLL page
Linear SearchLinear Search
A linear search is the process of examining a list, file or group of data to see if a given data item occurs in it.Sometimes called a serial search, this method involves looking at each data item in turn to see if there is a match with the value required.
1 prompt user to enter the number 2 set count to 1 3 while number is not array(count) AND count <> 10 4 add one to count 5 end while 6 if count =10 AND number is not array(count) 7 print number not in list 8 else 9 print number at position count 10 end if
Example Algorithm
HLL page
Count OccurrencesCount Occurrences
HLL page
This is the process of counting the number of times a data item occurs in a list, file or group of data.Based on the linear search it merely notes the number of times a match is found
1 prompt user to enter a name 2 set occur to zero 3 repeat for person 1 to 100 4 if name same as array(person) 5 add 1 to occur 6 end if 7 end loop 8 if occur=0 9 print name not in list 10 else 11 print it appears occur times 12 end if
Example Algorithm
Maximum and MinimumMaximum and Minimum
HLL page
This is the process of finding the largest or the smallest value in list, file or group of data
1 set max to zero 2 repeat for numbers 1 to 100 3 if array(number)>max 4 make max the array(number) 5 endif 6 end loop 7 print biggest value is max
Example Algorithm
The Algorithm for minimum would be the same except it would test for <min rather than >max