The Systems Engineering Context
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What Is Systems Engineering?
Systems Engineering is an interdisciplinary approach and means to enable the realization of
successful systems. It focuses on defining customer needs and required functionality
early in the development cycle, documenting requirements, then proceeding with design
synthesis and system validation while considering the complete problem:
• Cost & Schedule
• Training & Support
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Systems Engineering Context
• The problem
• Major principles of systems engineering
• Managing the system evolution
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1.1: The Problem
• Traditional approach
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• The quality and cost of software has been a
• Delivered long behind schedule
• At much higher cost than anticipated
• Without giving the desired benefits and user
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• It is hard to understand the purpose of a system well
enough to plan its functionality in advance so that it will
really satisfy the user needs.
• The complexity of systems and their dynamic behavior is
• The visibility nature of the product makes the development
and maintenance process itself difficult to understand and
• There is a lack of proven components to use as high level
building blocks. Too much is developed from scratch.
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• User: all those who interact directly with the system and
use the system service to achieve some operative purpose.
• Owner: people that will either own or be responsible for
the system during part of its lifetime.
• Subject: known to the system but does not directly
interact with it. (e.g. people and objects represented in a database)
• Developer: people that actually develop the system.
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• System quality is the systems ability to
satisfy the needs and expectations of the
user and the owners, i.e. the system
• Quality depends on clear and unambiguous
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Essence of Quality Control
• To ensure that each communication link and
transformation step worked as intended.
– Overall process: the organization of the development
process into major steps where specific documents are
produced and certain quality assessment procedures
– Technical content: the information content in the
various documents, e.g. requirements specification,
system specification, and test plans.
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The Traditional Approach
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1.2: Major Principles of
• Main descriptions
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• Systems engineering is performed by a system
consisting of people and tools called the project
system or the engineering organization.
• The end results of systems engineering are target
systems and their documentation, in the form of
• The role of a systems engineering methodology is
to help the engineering organization make target
systems right the first time and every time, within
budget and on time.
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The Role of Methodology
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• A methodology is made up of a set of methods
each of which is a systematic way of producing
• A methodology prescribes a set of descriptions
and associated methods.
• Each method provides guidelines for structuring
and using descriptions in given notations.
• A methodology is a collection of methods that a
system organization uses to achieve right quality,
short lead time and low cost.
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Symbolic representations of the subject matters
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Main Descriptions (I)
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Main Descriptions (II)
• Why the system is needed
– Requirements specification
• What its functionality should be
– Functional design
• How it should be implemented
– Implementation design
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• Clarify the needs of the user and the owner
• Write the needs down as requirements
• The requirements can be clearly understood
by the user, the owner, and the developer
• Focus on the purpose and role of the system
• Two categories: functional requirements
and non-functional requirements
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Product Or ganizational External
requir ements requir ements requirements
Ef ficiency Reliability Portability Interoperability Ethical
requir ements requir ements requirements requirements requirements
Usability Delivery Implementation Standards Legislative
requirements requirements requir ements requirements requirements
Performance Space Privacy Safety
requirements requir ements requirements requirements
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• Define the system functionality as clearly
and completely as possible
• Define the architecture of the technical
solution that will be used to realize the
• Be represented as functional design and
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• Focuses on the technical solution and its
relation to the functional design
• Forms the basis of the implementation of
the concrete system consisting of hardware
• Tells how the system is going to be realized
• Is derived from the functional design and
the non-functional requirements
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• The conformance between the requirement
specification and the system.
• Process quality vs system quality
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Benefits of Systems Engineering (I)
• Step-wise quality assurance can be performed
during the entire development.
• The user and owner needs are put into focus.
• The functionality can be validated at an early
• The number of aspects to be considered at each
step is reduced.
• The cost of error correction is reduced since error
can be detected earlier.
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Benefits of Systems Engineering (II)
• Different descriptions corresponds to different kinds
of expert knowledge.
• Language can be selected to fit the specific purpose
of each description.
• Description can be modified without affecting each
• The functional design documents the system as whole
independently of the implementation technology
chosen for the various parts.
• Each step provides a firm foundation for the next
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1.3: Managing the System Evolution
• Reference model (waterfall model)
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• Activity: the means of producing results
• Phase: period of time where specific activities are
carried out and results produced
• Baseline: phase result, basis for future work
• Milestone: phase transition
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Milestones and Baselines
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