A data flow diagram (DFD) is a graphical representation of data flow through a system. It shows what data is input and output from the system, what processes transform the data, and where data is stored. DFDs provide an overview of a system to communicate between users, analysts, and designers. A sequence diagram shows the interactions between objects in a system by displaying messages exchanged in time order. It models the dynamic behavior of the system and emphasizes the timeline of operations and message passing between objects. While a DFD focuses on data flow staticly, a sequence diagram illustrates the dynamic flow of control and processing through a system.

1. Presented By: Rafa Raheen

2. DFD(Data flow Diagram)
A data flow diagram (DFD) is a graphical
representation of the "flow" of data through
an information system, modeling
its process aspects. A DFD is often used as a
preliminary step to create an overview of the
system, which can later be elaborated. DFDs can
also be used for the visualization of data
processing (structured design).

3. Why DFD ?
Provide an overview of:
what data a system processes
what transformations are performed
what data are stored
what results are produced and where they flow
Graphical nature makes it a good
communication tool between:
user and analyst
analyst and system designer

4. External Entities
A rectangle represents an external entity
They either supply or receive data
They do not process data
Processes
A circle represents a process
Straight lines with incoming arrows are input data flow
Staright lines with outgoing arrows are output data flow

5. Data in motion
Marks movement of data through the system a piprline to
carry
Connect the processes, external entities and data stores
Data stores
A data store is a repository of data
Data can be written into the data store.this is depicted
by an incoming arrow
Data can be read from data store.this is depicted by an
outgoing arrow
External entity cannot be read or write to the data
store
Two data stores cannot be connected by a dafa flow

7. Various Levels of DFD
Level 0 DFD(Context diagram)
Shows an overall view of the system
It shows depict the system as a single bubble
All external entity interacting with the system should represented
in this diagram
level 1 DFD
This elaborate level 0 DFD and splits the process
into detailed form
Level 2 DFD
This elaborate level 1 DFD and displays the process
into more detailed form

10. Sequence diagram
Sequence diagram is interaction diagram that
shows the set of objects and messages send and
receive by those object.
It mainly emphases on time ordering and
messages.
It is used to illustrate the dynamic view of
system.
These are also called as “Isomorphic diagram”.

11. Terms and Concepts
Objects or Participants :-
 The sequence diagram is made up of collection of participants or objects.
Participants are system parts that interact each other during sequence
diagram.
 The participants interact with each other by sending and receiving message
 The object is represented by as below:
Object:Class_Name

12. Terms and Concepts
Lifeline:-
 Lifeline represents the existence of an object over a period of
time.
 It is represented by vertical dashed line.
 Most objects that appeared in ‘Interaction diagram’ will be in
existence for the duration of an interaction. So, these objects are
aligned at top at top of diagram with their lifeline from top to
bottom of diagram.

13. Terms and Concepts
Activation bar:-
 It is also called as focus of control. It shows the period of time during which
an object is performing an action.
 The top of rectangle is aligned with start of the action. The bottom is
aligned with its completion and can be marked by a written message
 It is represented by tall thin rectangle:

14. Terms and Concepts
Messages:-
 The interaction in a sequence diagram between the objects can be shown by
using messages.
 The messages on sequence diagram are specifies using an arrow from
participant that wants to pass the messages to the participant that receive
the messages .
 Messages can be flow in whatever direction required for interaction from
left to right and right to left.

15. Terms and Concepts
Messages:-
 It has following kinds of messages:
1)Synchronous messages:-
* It is a message where the sender is blocked and waits until
the receiver has finished processing of message.
* It is invoked the caller waits for the receiver to return from
the message invocation.
* It is represented by solid line with full arrow.
2)Asynchronous messages:-
* It is a messages where the sender is not blocked and can continue executing.
* It is represent by solid line with half arrow.

16. Terms and Concepts
Messages:-
 It has following kinds of messages:
3)Reflexive messages:-
* If the object sends the message to itself then it is called as ‘Reflexive message.
* It is represented by solid line with loops the lifeline of object.
4)Return messages:-
* It can be used at the end of activation bar to show that control flow of activation
returns to the participant that pass the original message.
* It is represent by dashed line from sender to receiver.

17. Terms and Concepts
Messages:-
 It has following kinds of messages:
5)Create messages:-
* It is used to create object during interaction.
* The object can be created by using <<create>> to indicate the timing of creation.
* Creating message can be shown as below:
6)Destroy messages:-
* It is used to destroy the objects during interaction.
* The objects can be terminated using <<destroy>> which points to an “x”.
* It indicates that object named message is terminated.

18. Terms and Concepts
Event:-
 It can be referred as smallest part of an interaction and event can occur of at any
given point in a Time.
 When interaction take place, Events are called as build in blocks for messages and
signals.
 Event is created while sending and receiving message.

19. Sequence diagram of Railway reservation
system

20. Difference between DFD & Sequence Diagram
DFD Sequence Diagram
 The purpose of DFD is to
show you how the data flows
through an information
system
 A DFD provides no
information about the timing
of processes or about whether
processes will operate.
 A sequence diagram shows
you information regarding
how the processes work
together and in what order
they operate
 In sequence which shows the
flow of control through an
algorithms, allowing a reader
to determine what operations
will be performed. It can also
trace the route that data
travels in a system, from start
to finish