System Analysis

SDLC (System development life cycle):

• "Waterfall"

• "Cascade"

• "Linear"

  CASE tool: (Computer Aid Software Engineering)

  • Context diagram (CD)

  • Data flow diagram (DFD)

  • Pert chart

  • Gantt chart (like a timeline)

• Tasks are done sequentially (one after the other)

  • e.g. after task one is executed, task 2 is run, and it continues on and on.

• Used in larger projects

• Have a number of steps that you have to execute:

  • e.g. making the bed, eating breakfast, etc.

• Six Main stages:

  1. Pre-analysis

     • "What is the problem?"

     • "What situation do I have to solve?"

     • Make an analysis of the situation, and what the potential options are.

     • Different steps:

       • Feasability Study (F.S.)

         • "Is it cost effective?"

         • "Is it worth doing?"

       • Define the Problem

         • "What is the problem?"

  2. Analysis

     • "What do you have to do?"

     • With the analysis break up into potential steps

     • Different Steps:

       • Model the "current system"

       • Requirements of the new system

  3. Design

     • "How can you solve the situation?"

     • Different Steps:

       • Logical Design

         • How does it work?

         • What do I need?

         • Specificatons?

         • Algorithms

         • pseudo-code

         • flow-charts

       • Physical Design

         • How does it look?

         • Where is it going to be stored?

         • actual code

     • Use context diagram

     • Use Data Flow diagram

  4. Develop

     • "What steps can I take to solve the issue?"

     • Steps taken:

       • Physical construction

       • Purchase hardware and software

  5. Implement

     • "This is how I will takle this?"

     • Steps taken:

       • Direct cut

         • Wasn't anything before, and you introduce something (new, and first time)

         • Introduced all at once

       • Phase

         • New system is 'phased' in, which repaces the older hardware/system

       • Pilot

         • Continually have new systems

           • Introduced bit by bit (once one has been implemented, implement new ones)

       • Parallel

         • Not replacing the older systems (using the new system in parallel to the old system)

  6. Evaluation/Maintenaince

     • Take information (through something like survey)

     • Maintain the new system

RAD (Rapid Application Development):

• Keeps cycling, until the result is satisfied (such as epochs in Machine Learning)

• Used mostly in smaller projeNcts

• flexible

• organic

• allows for movement

• can waste time and money

Context Diagrams:

• It is a data flow digram, with only one massive central process, subsumes everything inside of the scope of the system

• Represents how the system will recieve and send data flows to external entities involved.

Symbols:

• Circle: system is represented as a cirlce (what is processing it?)

• Curved arrow: data flow (where is the information going?)

• Square/rectangle: entities (such as customers)

DFD (Gane & Sarson): (Not used)

• rounded square: process

• straight arrow: data fow

• open ended retangle with a line through it: data store

• Source/Sink (external entitiy)

DFD symbols (DeMarco and Yourdon) The one we will be using:

• Circle: Process (has to have the word system), otherwise it could look like a process

• Straight arrow: data flow

• = : data store

• square: data source/sink (external entities)

Rules:

• Have to have a data input into the process

• Data has to be manipulated by the process

• Data has to be outputted

• Can't have 'miracles' (i.e. data that isn't being inputed, while having outputs)

• Can't have 'black-holes' (i.e. data going in and not going out)

• Can't have 'grey-holes' (i.e. manipulation of data is incorrect)

• Have to have processes (can't not use one)

Level-0 DFD:

• Shows the system's major processes, data flows, and data stores at a high level of abstraction

• After that you are able to go deeper into the system (where you go into 1.1, 1.2, 1.3, 1.4, etc.)

• Can be subdivided further (1.1.1, 1.1.2, 1.2.1, etc.)

• When the context diagram is expanded into DFD level-0, all the connections that flow into and out of process 0 needs to be retained.

Case:

1. Context Diagram

2. DFD (Level-0)

3. DFD (Level-1)

4. DFD (Level-2)

5. ... continues to DFD (Level-5)

Internal Data Flow:

• What happens within the system (between processes, databases, etc.)

External Data Flow:

• Things going into the data-flow and going out of the data flow

What is a balanced DFD? (First question in exam)

Level 1 Diagrams:

• Shows all processes (into a single process in the level 0 diagram)

• Shoes how information moves from and to to each of these processes

• etc.

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