02 - System

Question 1

What are the fundamental principles related to systems?

Answer 1

• Thinking with a systemic approach
• Reasoning according to an architecture paradigm

Question 2

What are the four considerations for thinking with a systemic approach?

Answer 2

• the objects of the reality are modeled as systems
• the system can be broken down into a set of smaller subsystems
• the system must be considered in interaction with other systems
• a system must be considered throughout its whole life cycle

Question 3

Explain how “the objects of the reality are modeled as systems” inside the systemic approach and give an example.

Answer 3

An object can be considered as a box performing a function and is defined by its perimeter, inputs, outputs, and internal state.

Example: Mobile Phone

• A system that takes in input a voice & keystrokes and outputs voices & displays.
• It can be on, off, or on standby.
• Overall, the phone allows one to make phone calls (among other functions).

Question 4

Explain how “the system can be broken down into a set of smaller subsystems” inside the systemic approach and give an example.

Answer 4

A system can be broken into subsystems. Each subsystem:
- is less than the whole system
- composition emerges new behaviors

Example: Mobile Phone

• is a screen, a keyboard, a body, a microphone, a speaker, and electronics.
• is the integration of all those elements
• cannot be understood completely from this set of elements.

Question 5

Explain how “the system must be considered in interaction with other systems” inside the systemic approach and give an example.

Answer 5

The system must be considered in interaction with its environment and other systems.

Example: Mobile Phone

• interacts with users, antennas (to transmit the signal), repairers (when broken), the ground (when falling), software, etc.
• All these systems
  • constitute its environment
  • shall be considered during its design.

Question 6

Explain how “a system must be considered throughout its whole life cycle” inside the systemic approach and give an example.

Answer 6

Considering the life cycle of a system means considering it from the moment it starts being produced and for any event, such as being sold, activated, switched on/off, malfunctioning, etc.

Example: Mobile Phone

• is designed, prototyped, tested, approved, manufactured, distributed, sold, used, repaired, and finally recycled.
• All these steps are important (and not only the moment when it is used).

Question 7

What are the five considerations for reasoning according to an architecture paradigm?

Answer 7

• a system can be linked to another through an interface
• a system can be considered at various abstraction levels
• a system can be viewed according to several layers
• a system can be described through interrelated models with given semantics
• a system can be described through different viewpoints

Question 8

Explain how “a system can be linked to another through an interface” inside the architecture paradigm approach and give an example.

Answer 8

A system can be linked to another through an interface that will model the properties of the link. The link requirements will model the provided interfaces.

Example: Mobile Phone

• our ear is in direct contact with the phone, and there is, therefore, a link between the two systems -the ear and the phone
• there is a hidden interface: the air. The properties of the air may influence the link between the ear and the phone (for example, if there is a lot of noise).

Question 9

Explain how “a system can be considered at various abstraction levels” inside the architecture paradigm approach and give an example.

Answer 9

A system can be considered at various abstraction levels, allowing it to consider only relevant properties and behaviors.

Example: Mobile Phone

• a device to make phone calls
• a device to take photos
• a set of material
• electronics components manufactured together
• All these visions are realistic but at different abstraction levels. Relevancy depends on the context.

Question 10

Explain how “a system can be viewed according to several layers” inside the architecture paradigm approach and give an example.

Answer 10

A system can be viewed according to several layers:

• its sense: why is it being produced? (offered functionality (Why?)
• functions: operation to fulfill offered functionality (What?)
• composition: definition of components necessary to implement the functions (How?)

Example: Mobile Phone

The phone is an object.

• whose sense is to accomplish several missions for its environment
  • making phone calls, being a fashionable object, offering various features of personal digital assistants, etc.
• is a set of functions organized to accomplish these missions:
  • displaying on the screen, transmitting a signal, delivering power supply, looking for user inputs, making noise if necessary, etc).
• physical components implement these functions:
  • Antenna, communication co-processor, network stack

Question 11

Explain how “a system can be described through interrelated models with given semantics” inside the architecture paradigm approach and give an example.

Answer 11

• properties that the system should provide (requirements)
• structure of the various components (how they interact)
• states of the system
• behaviors of the system
• manipulated data, etc
• described with SysML

Example: Mobile Phone

• From the point of view of properties, the phone is a device expected to meet requirements such as
  • “a phone must resist falls from a height of one meter”.
• But a phone will also change state :
  • when a phone is off, and the power button is pressed, the phone shall turn on.
• Function dynamics of the phone are also relevant:
  • when receiving a call, the screen will display the name, and the speaker will buzz, but if the user presses no button, the phone will stop after 30 seconds.

Question 12

Explain how “a system can be described through different viewpoints” inside the architecture paradigm approach and give an example.

Answer 12

• corresponding to various actors concerned by the system
• all these visions are important and define the system in multiple and complementary ways
  • commercials, designers, engineers (in charge of software, electronics, acoustics, materials, etc), users, repairers, etc

Example Mobile Phone

Different stakeholders view a phone in different ways:

• the designer will see the phone as an easy-to-use object centered on the user,
• the engineer will see it as a technological device that has to be efficient and robust.
• the commercial may rather see it as a product that must meet clients’ needs and market trends to be sold.