DATA AND PROCESS
MODELING
PROCESSING MODELLING
Process modelling aims to graphically represent the processes
which capture, manipulate, store and distribute data.
• data flow diagrams
• function decomposition
• structured English
• decision tables and decision trees
Data flow diagrams model
Data flow diagrams model the flow of data into,
through, and out of an information system
• show the processes that change or transform data
• show the movement of data between processes
• represent a system as a network of processes
which transform data flowing between them
DATA FLOW DIAGRAM (DFD) COMPONENTS
Entities( External Agent (Source/Sink))
Entities include source and destination of the data. Entities
are represented by rectangle with their corresponding
names.
• An external agent represents an entity with which the system communicates and
which is outside the scope of the system e.g. an outside organization or individual,
another department or another system, a person or group within the department
supported by the system who interacts with the system
• an external agent is a source if it is an origin of data coming into
the system
• an external agent is a sink if it is a destination of data leaving the
system
Process:
The tasks performed on the data is known as process. each process has a
unique number and name.
• name each process using a verb and a noun phrase
• the name of a process should describe what the process does
• eg. calculate price ,check customer details ,accept supplier delivery
Data Flow:
a data flow represents data in motion, moving from one place in the system
to another.
The movement of data in the system is known as data flow. It is represented
with the help of arrow. The tail of the arrow is source and the head of the
arrow is destination.
Loan application
• name each data flow using a noun or noun phrase
e.g.. customer order
The name should include as much information as possible about the data
flow e.g. "customer payment" rather than just "payment
Data Storage:
Data storage includes the database of the system. It is represented by
rectangle with both smaller sides missing or in other words within two
parallel lines.
• The name should describe the contents of the data store
• A data store may represent many different types of physical locations of
data
• A data store may be a temporary or a permanent repository of data
Guidelines for Drawing DFDs
each object on a data flow diagram must have a unique name
2. each process must have at least one data flow coming in (input) and at
least one data flow going out (output)
3. the inputs to a process are different from the outputs of that process
4. a process must be able to build its outputs using only the information in
its input data flows plus any constant
1.
Data flows are permitted:
• between processes
• from a data store to a process
• from a process to a data store
• from a source to a process
• from a process to a sink
• data flows are NOT permitted:
• between external agents
• between data stores
• from an external agent to a data store
DFD LEVEL 0
A context diagram is a data flow diagram that only shows the top level,
otherwise known as Level 0. At this level, there is only one visible process node
that represents the functions of a complete system in regards to how it interacts
with external entities. Some of the benefits of a Context Diagram are:
• Shows the overview of the boundaries of a system
• No technical knowledge is required to understand with the simple notation
• Simple to draw, amend and elaborate as its limited notation
EXAMPLE: Food Ordering System
The figure below shows a context Data Flow Diagram that is drawn for a Food
Ordering System. It contains a process (shape) that represents the system to
model, in this case, the "Food Ordering System". It also shows the participants
who will interact with the system, called the external entities. In this example,
the Supplier, Kitchen, Manager, and Customer are the entities who will interact
with the system. In between the process and the external entities, there is data
flow (connectors) that indicate the existence of information exchange between
the entities and the system.
DFD LEVEL 1
• The Food Order System Data Flow Diagram example contains three
processes, four external entities, and two data stores.
• Based on the diagram, we know that a Customer can place an Order. The
Order Food process receives the Order, forwards it to the Kitchen, store it in
the Order data store, and store the updated Inventory details in the Inventory
data store. The process also delivers a Bill to the Customer.
• The Manager can receive Reports through the Generate Reports process,
which takes Inventory details and Orders as input from the Inventory and
Order data store respectively.
• The Manager can also initiate the Order Inventory process by providing
Inventory order. The process forwards the Inventory order to the Supplier and
stores the updated Inventory details in the Inventory data store.