DFD examples

steps Create a list of activities Construct Context Level DFD (identifies external entities and processes) Construct Level 0 DFD (identifies manageable sub process ) Construct Level 1- n DFD (identifies actual data flows and data stores ) Check against rules of DFD

External entities … noun Data flows .. Name of data Process ..verb phrase ( system name , sub sytem name) Data store ..noun

(draw your context diagram)

Level-0 DFD

Consider the following DFD. List two errors on this DFD 1.0 P2 E1 DF5 DS1 DF6 DF3 DF1 DF4 2.0 P1 DF2 E2

Logizian Analyst edition http://www.visual-paradigm.com/product/lz/tutorials/dfd.jsp

Ordering a tuna roll

Ordering some lunch Tuna roll please! The customer A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll.

The waitresses write this down and passes the order to the chef. Ordering some lunch The waitresses Order 1 x Tuna roll Order 1 x Tuna roll The waitresses write this down and passes the order to the chef.

Ordering some lunch Order The chef Order 1 x Tuna roll The chef gets the order and makes the roll. The roll is then passed back to the waitress.

The customer pays their bill. Ordering some lunch Coffee Control 1 tuna roll RM 2.99 Thank you The waitresses The customer Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the cash till. This shows how much the customer owes. The customer pays their bill.

Ordering some lunch The waitresses The customer When the food arrives from the chef, the waitress gives it to the customer.

Information flow The next few slides demonstrate how to produce the data flow diagram – this example is for ordering a tuna roll.

Analyse the problem Put a square around any inputs or outputs involved - these are entities. Circle any data stores. Underline any processing that takes place Sketch out the information flow, joining up the people (entities, the processing and the data stores

Square around inputs and outputs A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

Circle data stores A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

Underline any processing A customer wants to order some lunch. They walk to the counter and ask for the menu. They make their choice and ask the waitress for a tuna roll. The waitresses write this down and passes the order to the chef. The chef gets the order and makes the roll. The roll is then passed back to the waitress. Whilst the chef makes the roll, the waitress gives the customer a paper bill produced from the till. This shows how much the customer owes. The customer pays their bill. When the food arrives from the chef, the waitress gives it to the customer.

DFD Symbols External Entity Flow of Data Process Data Store Customer Chef Bill Flow of Data Process Preparing a bill Menu Data Store

The customer and the chef are ENTITIES Who are the ENTITIES? Customer Chef The customer is a source of information – the person who start the whole process off. The chef is a destination of the information. The customer and the chef are ENTITIES

What is a DATA STORE The menu is a DATA STORE Customer Chef The menu or price list keeps a record of prices – it is a data store. Sandwich prices The menu is a DATA STORE

The waitress is a process Who is a process? Order sandwich Customer Chef The waitress processes the order The waitress is a process Sandwich prices The waitress is not shown as an entity because she does not produce or receive information (ultimately – the order goes to the chef!!). She is not a data SOURCE or SINK!

The arrows indicate data flows 1. order Customer Order sandwich 5. invoice 2. order Chef 6. payment 8. Tuna 7. receipt 9. Tuna 4. price 3. query price Sandwich prices The arrows indicate data flows The final Data Flow Diagram

Before you start! A few rules to follow!!

There must always be a process between entities! Customer Chef X wrong! There must always be a process between entities!

Information flows must NEVER cross! Customer Order sandwich Chef X wrong! Sandwich prices Information flows must NEVER cross!