Software Development
Year 10
Analysis
CONTEXT DIAGRAMS
To initially analysis the problem your software is going to solve it is best to start with a context diagram. The diagram is contained in a rectangle which represents the environment where the software will be used. For example; An office, at home, in a school, in a vehicle etc. The Circle represented the whole software solution and the user is now called an Entity. An entity is a person or thing (it can also be an outside database).
Context diagrams can be very useful when multiple users and outside organisations are connecting to the system you are building.
USE CASE DIAGRAMS
Use Case displays the way a solution will be used. Rather than writing a complex algorithm to solve the problem, the first stage is to identify the system in terms of it's users and what each "CASE" will be. Each CASE is a how a user interacts with the solution.
You create a USE CASE in 6 STEPS:
1. Create the System boundary
2. Identify the actors (the users roles)
3. Identify each CASE the user will interact with
4. Create associations between Actors and CASES
5. Add extra CASEs where there are more than one step required (includes)
6. Add extra CASEs where there may be an extra step involved on occasion(extends)
DATA FLOW DIAGRAM
It is important to know the structure of DFDs. First you must begin with a Context Diagram which is the highest level of DFD. It displays the system as a whole and how data flows in and out of the system to and from entities.
The Next Layer DFD takes the Context Diagram and adds up to 8 key processes that represent the solution. Please take care to use the all the rules as layered out on pages 42 - 43 of Adrian Jansen's text book:
A DFD contains: Processes, Enitities, Data Flows and Data Stores.
1. Reading the diagram should start at the top left and move to the bottom right.
2. Data can't flow entity to entity
3. Data from a Data Store must go through a process before going to another Data Store
4. A process must have data in and data out. Don't leave them hanging
5. Data coming out of a process must be different to the data entering it.
6. rejected data can be sent out of the diagram
7. Keep the DFD to 8 processes at the 2nd level
8. Use good processing verbs in your processes: Calculate, edit, delete, sort, add.
