it systems analysis and design

Btec National - IT SYSTEMS ANALYSBtec National - IT SYSTEMS ANALYSIS AND DESIGNIS AND DESIGN

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IT Systems Analysis and IT Systems Analysis and DesignDesign

SSADM – DesignSSADM – Design


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AimsAims

Learn about Data Flow Diagrams (DFDs) Learn about Data Flow Diagrams (DFDs) and what they are used for.and what they are used for.

Be able to create context DFD and Level Be able to create context DFD and Level one DFDone DFD

Gain an insight into further levels of detail Gain an insight into further levels of detail (DFD)(DFD)


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Data Flow DiagramsData Flow Diagrams

DFDDFD– Data flows are used to show how a system Data flows are used to show how a system

will/does operate.will/does operate.

– They show how the data flows around the They show how the data flows around the system.system.


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DFDDFD

– Data flow diagrams show the system Data flow diagrams show the system boundary, the external entities, the processes boundary, the external entities, the processes and the data stores.and the data stores.


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External entities – things External entities – things outsideoutside the system, the system, such as people, organisations and other such as people, organisations and other systemssystems

Customer


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Process, should always start with an active verb. The Process, should always start with an active verb. The number in the corner is used to identify the parent number in the corner is used to identify the parent

process and to uniquely identify this process.process and to uniquely identify this process.

Calculate Benefit

1.3

Unique ID

Process description


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Data Flow DiagramsData Flow DiagramsData StoreData Store– This is used to store and retrieve data from, This is used to store and retrieve data from,

these are not shown at level 0 (context these are not shown at level 0 (context diagram)diagram)

Unique ID

Data store name

Customer DetailsD8


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Data Flow DiagramsData Flow DiagramsAs in Yourdon diagrams, a flow is shown by a line with a As in Yourdon diagrams, a flow is shown by a line with a flow name and an arrow at the destination end, e.g.flow name and an arrow at the destination end, e.g.

The data flow name must be a noun The data flow name must be a noun (i.e. a thing not an activity)(i.e. a thing not an activity)

Data flows may only go:Data flows may only go: between two processes;between two processes; between an entity and a process;between an entity and a process; between a data store and a process.between a data store and a process.

Data flow lines don’t merge or split Data flow lines don’t merge or split (but more than one line can go to/from the same (but more than one line can go to/from the same entity, process or data store)entity, process or data store)

Data flows must not cross Data flows must not cross (use duplicate entities and/or data stores to avoid crossing(use duplicate entities and/or data stores to avoid crossing lines)lines)

Customer address


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Context DiagramContext Diagram– A context diagram is the highest level DFD A context diagram is the highest level DFD

(general overview), it shows the data flows, (general overview), it shows the data flows, external entities, the process (system in external entities, the process (system in focus, don’t be tempted to divide the process focus, don’t be tempted to divide the process into too many steps or the diagram will into too many steps or the diagram will become too complicated)become too complicated)


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Context Diagram (high level) – Example (Notice no data stores)Context Diagram (high level) – Example (Notice no data stores)

Booking confirmation

Booking detailsCustomer

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Create Booking


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Moving from high-level to low-level– The high level DFD needs to be broken down into more detail

(decomposed) to produce a low-level DFD.

– The first step is to divide the identified process in the context DFD into several, more detailed processes.

– This is generally performed by using the information gathered so far to determine what the divided processes should be.

– Some analysts say as a rule of thumb there should be a single process dealing with each data flow attached to an external entity.


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1.1

Check Availability

1.2

Record new booking

1.3

Confirm booking

CustomerD1 Room Booking

Details

D2 Customer Details

Booking details

CustomerCustomer details

Room booking details

Customer details

Booking details

Booking confirmation

Availability details

Notice the system boundary


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Moving from Level 1 to Level 2– A level 1 may need breaking down again into further

processes i.e. if the confirm booking process (1.3) was complicated then that process could be broken down further to detail the complexities. The process IDs would start with 1.3.1, 1.3.2 etc.

– This would continue until the analyst is satisfied that he/she has a clear understanding.


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ConclusionConclusion

Learned about Data Flow Diagrams Learned about Data Flow Diagrams (DFDs) and what they are used for.(DFDs) and what they are used for.

We created context DFD and Level one We created context DFD and Level one DFDDFD

Gained an insight into further levels of Gained an insight into further levels of detail (DFD)detail (DFD)

it systems analysis and design

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