System modeling is the process of developing abstract models of a system using graphical notations like the Unified Modeling Language (UML) to represent different views of a system. Models help analysts understand system functionality and communicate with customers. Models of existing and new systems are used during requirements engineering to clarify current systems, discuss strengths/weaknesses, and explain proposed requirements.

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 System modeling is the process of developing abstract
models of a system, with each model presenting a
different view or perspective of that system.
 System modeling has now come to mean representing a
system using some kind of graphical notation, which is
now almost always based on notations in the Unified
Modeling Language (UML).
 System modelling helps the analyst to understand the
functionality of the system and models are used to
communicate with customers.

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 Models of the existing system are used during
requirements engineering. They help clarify what the
existing system does and can be used as a basis for
discussing its strengths and weaknesses. These then lead
to requirements for the new system.
 Models of the new system are used during requirements
engineering to help explain the proposed requirements
to other system stakeholders. Engineers use these
models to discuss design proposals and to document the
system for implementation.
 In a model-driven engineering process, it is possible to
generate a complete or partial system implementation
from the system model.

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 An external perspective, where you model the context
or environment of the system.
 An interaction perspective, where you model the
interactions between a system and its environment, or
between the components of a system.
 A structural perspective, where you model the
organization of a system or the structure of the data
that is processed by the system.
 A behavioral perspective, where you model the dynamic
behavior of the system and how it responds to events.

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 The Unified Modelling Language is a standard graphical
language for modelling object oriented software.
 In 1997 the Object Management Group (OMG) started the
process of UML standardization
 The objective of UML is to assist in software
development
 It is not a methodology

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 Activity diagrams, which show the activities involved in a
process or in data processing .
 Use case diagrams, which show the interactions between
a system and its environment.
 Sequence diagrams, which show interactions between
actors and the system and between system components.
 Class diagrams, which show the object classes in the
system and the associations between these classes.
 State diagrams, which show how the system reacts to
internal and external events.

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 System Context Diagrams are diagrams used in systems
design to represent the more important external actors
that interact with the system at hand.
 This type of diagram usually pictures the system at the
center, with no details of its interior structure, surrounded
by all its interacting systems, environment and activities.
 The objective of a system context diagram is to focus
attention on external factors and events that should be
considered in developing a complete set of system
requirements and constraints.

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 Identify the system and its boundaries (the context)
 Identify external entities (providers, receivers of system
info)
 Identify external data flows (input, output)
 However, NO DATA STORE !!!
 Note: The whole system itself is a process (it receives
input and transforms into output)

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 Assumption: there is no revise order option
Customer
Vending
Machine
System
Send order
Submit order

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 Assumption: ONLY withdrawing money (not transfer,
checking balance, or other services….)
Customer
ATM
System
Complete transaction
Or
Revise transaction
Request transaction

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 A student sends in an application form containing their
personal details, and their desired course
 The university checks that the course is available.
 If the course is available and the student is enrolled in
the course, the university confirms the enrolment by
sending a confirmation letter that they are registered
for the course to the student.
 Or if the course is unavailable the student is sent a
rejection letter.
 What system is being modeled?

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 Letters of complaint received from citizens are entered
into a complaints master file by the City Clerk’s office. The
date, department code, and a complaint description are
stored for each letter. Weekly reports are produced from
the complaints master file and given to the City Manager.
Two weekly reports are produced: a department summary
and a detail report of complaint.

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