Unit 3 Software Development Flashcards
Analysis
Stakeholders state what they require from the finished product. This information is used to clearly define the problem and the system requirements. Requirements may be defined by:
- Analysing strengths and weaknesses with current way this problem is being solved
- Considering types of data involved including inputs, outputs, stored data and amount of data
Design
The different aspects of the new system are designed, such as:
- Inputs: volume, methods, frequency
- Outputs: volume, methods, frequency
- Security features: level required, access levels
- Hardware set-up: compatibility
- User interface: menus, accessibility, navigation
A test plan may also be designed at this stage.
Development and testing
The design from the previous stage is used to split the project into individual,
self-contained modules, which are allocated to teams for programming.
Alpha testing
Alpha testing is carried out in-house by the software development teams within the company. Bugs are pinpointed and fixed.
Beta testing
Beta testing is carried out by end-users after alpha testing has been completed. Feedback from users is used to inform the next stage of development.
White box testing
This is a form of testing carried out by software development teams in which the test plan is based on the internal structure of the program. All of the possible routes through the program are tested.
Black box testing
This is a form of testing where the software is tested without the testers being aware of the internal structure of the software and can be carried out both within the company and by end-users. The test plan traces through inputs and outputs within the software.
Implementation
Once the testing stage has been used to make the appropriate changes to the software, it is installed onto the users’ systems.
Evaluation
After the implementation stage, the effectiveness of the software is evaluated against the system requirements defined at the analysis stage to evaluate its suitability in solving the problem. Different criteria are considered, including robustness, reliability, portability and maintainability.
Maintenance
Any errors or improvements that could be made to the software are flagged up by the end-users. Programmers will regularly send out software updates to fix any bugs, security issues or make any needed improvements.
Waterfall lifecycle
The waterfall model is based on a series of stages which are completed in sequence, from start to finish.
The analysis stage includes a feasibility study in which designers evaluate the feasibility of the project using ‘TELOS’: Technical, Economic, Legal, Operational, Scheduling
If a change needs to be made within a project being developed using the waterfall model, programmers must revisit all levels between the current stage and the stage at which a change needs to be made. This makes the model inflexible and so unsuitable to projects with changing requirements. This also means that users have little input as they are only involved at the very beginning and end of the waterfall lifecycle, during the analysis and evaluation stage.
Agile methodologies
The problem is broken down into sections which are developed in parallel. The design and analysis phase often occur together. Different sections of software can be at different stages of development. A working prototype is delivered early on and prototypes are built upon and improved in an iterative manner so that new prototypes are delivered regularly throughout the course of the development cycle.
Extreme programming
This is an agile model in which the development team consists of a pair of programmers alongside a representative end-user. The model is built on ‘user stories’: system requirements are specified by the end-user and used when designing the program. The aim of paired programming is to produce high-quality code, as the code is written by one person and critiqued by the other so is improved as it is written. Programmers work no longer than forty hours a week with the aim that quality is not compromised. Each iteration through the cycle generates what is called a ‘working version’ of the program which means it could function as the final product.
Spiral model
The spiral model is built on four key stages
with the focus of effectively managing risk-heavy projects:
- Analysing system requirements
- Pinpointing and mitigating risks
- Development, testing and
implementation
- Evaluating to inform the next iteration
If the project is found to be too risky at any point, the project is terminated. However hiring risk assessors to analyse the risks involved can be expensive, which makes this methodology suited to only very large-scale projects.
Rapid application development
RAD is an iterative methodology which uses partially functioning prototypes which are continually built-upon. User requirements are initially gathered using focus groups and used to develop an ‘incomplete’ version of the solution which is given to the user to trial. User feedback is then used to generate the next, improved prototype and this continues until the prototype matches the requirements of the end-users at which point it becomes the final product.
Algorithm
An algorithm is a set of instructions used to solve a problem. They are core to computer science and can be used to tackle a wide range of problems
Programming paradigms
Programming paradigms are different approaches to using a programming language to solve a problem. They are split into two broad categories - imperative and declarative - which can be broken down further into more specific paradigms. The imperative programming paradigm includes the procedural and object-oriented paradigms while the declarative paradigm is split into logic and functional paradigms. The paradigm used depends on the type of problem that needs solving.
Imperative
Imperative programming paradigms use code that clearly specifies the actions to be performed.
Procedural
Procedural programming is one of the most widely-used paradigms as it can be applied to a wide range of problems and is relatively easy to write and interpret. This is a type of imperative programming which uses a sequence of instructions which may be contained within procedures. These instructions are carried out in a step-by-step manner.
Examples: Pascal, Python, Logo
Object-oriented
Object-oriented programming (referred to as OOP) is another popular paradigm as it is applicable to certain types of problem with lots of reusable components which have similar characteristics. OOP is built on entities called objects formed from classes which have certain attributes and methods. OOP focuses on making programs that are reusable and easy to update and maintain.
Examples: Python, Delphi, Java
Declarative
Declarative programming focuses on stating the desired result rather than the exact series of instructions that need to be performed to get to the result. It is the role of the programming language to determine how best to obtain the result and the details about how it is obtained are abstracted from the user. This type of programming is common in expert systems and artificial intelligence.
Functional
Functional programming uses the concept of reusing a set of functions, which form the core of the program. Programs are made up of lines of code consisting of function calls, often combined within each other. Functional programming is closely linked to mathematics.
Examples: Haskell, C#, Java
Logic
Logic languages are also part of the declarative programming paradigm and use code which defines a set of facts and rules based on the problem. Queries are used to find answers to problems.
Example: Prolog
Procedural language
Procedural programming is used for a wide range of software development as it is very simple to implement. However, it is not possible to solve all kinds of problems with procedural languages or it may be inefficient to do so.
Procedural languages use traditional data types such as integers and strings which are built into the language and also provide data structures like dictionaries and arrays.
Structured programming
Structured programming is a popular subsection of procedural programming in which the control flow is given by four main programming structures:
- Sequence
Code is executed line-by-line, from top to bottom.
- Selection
A certain block of code is run if a specific condition is met, using IF statements.
- Iteration
A block of code is executed a certain number of times or while a condition is met. Iteration uses FOR, WHILE or REPEAT UNTIL loops.
- Recursion
Functions are expressed in terms of themselves. Functions are executed, calling themselves, until a certain condition known as a base case (which does not call the function) is met.
Assembly language
Assembly language is the next level up from machine code and is part of a family of low level languages. This is converted to machine code using an assembler when it is executed.
Assembly language uses mnemonics rather than binary, which makes it easier to use than direct machine code.
Each mnemonic is represented by a numeric code.
However, the commands that assembly language uses are processor-specific as it directly interacts with the CPU’s special purpose registers. This allows for direct interaction with hardware so is useful in embedded systems. Typically, each instruction in assembly language is equivalent to almost one line of machine code.
Mnemonic, Instruction
ADD Add SUB Subtract STA Store LDA Load INP Input OUT Output HLT Halt DAT Data BRZ Branch if zero BRP Branch if positive BRA Branch always
ADD
Add the value at the given memory address to the value in the Accumulator
SUB
Subtract the value at the given memory address from the value in the Accumulator
STA
Store the value in the Accumulator at the given memory address
LDA
Load the value at the given memory address into the Accumulator
INP
Allows the user to input a value which will be held in the Accumulator
OUT
Prints the value currently held in the Accumulator
HLT
Stops the program at that line, preventing the rest of the code from executing.
DAT
Creates a flag with a label at which data is stored.
BRZ
Branches to a given address if the value in the Accumulator is zero. This is a conditional branch.
BRP
Branches to a given address if the value in the Accumulator is positive. This is a conditional branch.
BRA
Branches to a given address no matter the value in the Accumulator. This is an unconditional branch.
Immediate Addressing
The operand is the actual value upon which the instruction is to be performed, represented in binary,
Direct Addressing
The operand gives the address which holds the value upon which the instruction is to be performed. Direct addressing is used in LMC.
Indirect Addressing
The operand gives the address of a register which holds another address, where the data is located.
Indexed Addressing
An index register is used, which stores a certain value. The address of the operand is determined by adding the operand to the index register. This is necessary to add an offset in order to access data stored contiguously in memory such as in arrays.
