1 Data Flow Diagrams. 2 Identifying Data Flows During the analysis stage of a project it is...
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Transcript of 1 Data Flow Diagrams. 2 Identifying Data Flows During the analysis stage of a project it is...
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Identifying Data Flows
During the analysis stage of a project it is important to find out how data flows through a system:
Where does the data originate?
What processing is performed on it and by whom?
Who uses the data?
What data is stored and where?
What output is produced and who receives it?
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DATA FLOW DIAGRAMS [DFDS]
A diagram to show how data is captured, processed, stored and distributed within a system.
This is generally represented during the analysis stage of a project, but can be further refined during the design stage to show more detail of how the system functions.
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PROCESS
DATA FLOW
E.g. Result of a query to a database, contents of a printed report : data that moves together to common destinations
Actions performed on data so that they are transformed, stored or distributed. This can be a computerised or manual transformation
SYMBOLS USED IN A DFD
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DATA STORE
A physical location to hold data e.g. a file folder or notebook etc.
SYMBOLS USED IN A DFD
Origin and/or destination of the data. Often referred to as external entities (source or sink)as they are outside the system. We are only interested in how data flows in to or from the system to them.
DATA SOURCE
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It is often impossible to represent a complete business on one diagram. For this reason it is quite common to use more than one level of Data Flow Diagram with each level showing more detailed information about part of the previous diagram.
It is important that the diagram should be made as clear as possible and for this reason it is not uncommon to draw the same source or sink [external entity] more than once to help achieve this.
How Much Detail ?
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Main steps when constructing a Level 0 Diagram :
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the correct symbols
Link them with data flows that are labelled
Context or Level 0 Diagram
The highest level view of a system. This only has one process which represents the overall function of the system and has no data stores as all the data is stored
within the process.
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Constructing a Level 1 diagram
Identify and draw the processes that make up the Level 0 process
Allocate descriptions to these
Lay out the sources/sinks and data flows from the Level 0 diagram
Draw in any data stores used in the process
Link the new processes and data stores with named data links
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IF it is necessary to produce a level 2 or level 3 diagram, the same steps
would be followed as used when constructing the Level 1 diagram
Constructing a Level 2/3 diagram
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Here is an example of how Data flow diagrams would be used to
model the logic of data flows in a small business that fits kitchens.
Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the correct symbols
Link them with data flows that are labelled
1. Context or Level 0 Diagram
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Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the correct symbols
Link them with data flows that are labelled
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Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out in a diagram using the correct symbols
Link them with data flows that are labelled
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Level 0 Context diagram
Customer Kitchen Fitter
Owner/Manager
Supplier
Kitchen Invoicing
and supply system
0
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Identify where data is captured from
Identify where data is distributed to
Describe the overall process
Map these out using the correct symbols
Link them with data flows that are labelled
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Level 0 Context diagram
Customer Kitchen Fitter
Owner/Manager
Supplier
Kitchen Invoicing
and supply system
0Customer Order
Invoice/quotes
Job Details
Product requestsProduct details
Management reports
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Constructing a Level 1 diagram
Identify and draw the processes that make up the Level 0 process
Allocate descriptions to these
Lay out the sources/sinks and data flows from the Level 0 diagram
Draw in any data stores used in the process
Link the new processes and data stores with named data links
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Level 0 Context diagram
Customer Kitchen Fitter
Owner/Manager
Supplier
Kitchen Invoicing
and supply system
0Customer Order
Invoice/quotes
Job Details
Product requestsProduct details
Management reports
Does this show enough detail?
2020
It is essential that you have a clear idea of EXACTLY what you wish to model.
Examples may be:
creating an invoice
Adding a supplier/customer/product
Searching for supplier/customer/product
Running a backup procedure
Archiving
Level 1 diagram
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Creating an invoiceCreating an invoice
• Created by: only the manager can do Created by: only the manager can do thisthis
• How often: either monthly or ad-hocHow often: either monthly or ad-hoc
• Inputs: Customer details (ref) and datesInputs: Customer details (ref) and dates
• Output medium: A4 paperOutput medium: A4 paper
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Creating an invoice for Creating an invoice for products collected between products collected between two datestwo dates• List what you need on the invoice, in detail List what you need on the invoice, in detail
(assume it is all in the system and you (assume it is all in the system and you only need to get it out)only need to get it out)– Customer details: name, address, phone, Customer details: name, address, phone,
postcode, email postcode, email – Product name, unit price, reference number, Product name, unit price, reference number,
descriptiondescription– Order details, date(s) of purchase, quantity, Order details, date(s) of purchase, quantity,
product, totalproduct, total– Invoice details: period start/end date, invoice Invoice details: period start/end date, invoice
date (because we are creating the invoice date (because we are creating the invoice these may need to be created at request time these may need to be created at request time and written back to the relevant data store)and written back to the relevant data store)
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Owner/Manager
customer data
Customer name/ref
Get customer name
Customer name/ref
Get start date
and end date
dates
order data
dates
list product
Id numbers between dates
Get product
details
product data
Sort into
groups
by customer
Generate
invoicePrint invoice
Customer
Customer details
Dates & product Id
product Id
product Idproduct details
dates
Invoice details
Invoice details
Invoice
Add invoice
date
Invoice date
Invoice date
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So that’s about as complex as So that’s about as complex as we need we need
• You can have level 1 DFDs that just You can have level 1 DFDs that just have one entity one process and one have one entity one process and one data storedata store