M150: Data, Computing and information
Outline
1.Unit sixteen: Realistic expectations
2.Review questions.
3.Your questions.
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1- Unit sixteen: Introduction
In this Unit:
The digital computer, the success of the twentieth century
Reaction to the rise of ICT
What can go wrong with computer applications
What computers cannot do or should not do
Ethics and computing
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The digital computer, the success of the twentieth
century
The invisible computer
The story is similar to “home electric motor” of the early 19th
Interesting tools: the GPS
Parallel computing
Moore’s law: interesting expectations
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The OSI Model
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OSI model Layers
Layer 1. Physical Layer: Defines the physical [hardware]
implementation and the electrical [signal level] implementation
of the bus; network cabling, connector type, pin-out, physical
data rates, maximum transmission distances, and data
transmission encoding.
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OSI model Layers
Layer 2. Data Link layer: Frame format, Transmitting frames
over the net [additional bit/byte stuffing, start / stop flags,
checksum, and CRC]. CAN bus, ATM, StarLAN, LocalTalk
and HDLC are layer 2 protocols. Different network and
protocol characteristics are defined by different data link layer
specifications.
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OSI model Layers
Layer 3. Network Layer: Provides address assignment, and
Packet's forwarding methods. Protocol Data Unit [PDU] is
called a Packet at this layer. This layer responds to service
requests from the Transport Layer and issues service requests to
the Data Link Layer.
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OSI model Layers
Layer 4. Transport Layer: Provides transfer correctness, data
recovery, and flow control. TCP is a layer 4 protocol. Protocol
Data Unit [PDU] is called a Segment at this layer. This layer
responds to service requests from the Session Layer and issues
service requests to the Network Layer.
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OSI model Layers
Layer 5. Session Layer: Establishing a communication
session, Security, Authentication. NetBIOS is a layer 5
protocol. Protocol Data Unit [PDU] is called Data at this layer.
This layer responds to service requests from the Presentation
Layer and issues service requests to the Transport Layer.
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OSI model Layers
Layer 6. Presentation Layer: Determines how computers
represent data [ASCII, GIF..]. Protocol Data Unit [PDU] is
called Data at this layer. This layer responds to service requests
from the Application Layer and issues service requests to the
Session Layer.
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OSI model Layers
Layer 7. Application Layer: The highest layer. Generates or
interprets data, may also provide encryption or decryption.
Applications using the network learn how to send a request,
how to specify a filename over the net, how to respond to a
request.
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The responses of individuals
The optimists
The pessimists
The realists
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What can go wrong
Dependence and risk
Hardware failure
Software crisis (the Y2K exemplary)
Inadequate requirements
Incorrect coding
Infeasibility of testing
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What can go wrong
Inadequate models
Over maintained code
The swing project
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Inadequate model
The Swing project
This is how the
customer explained it
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This is how the project
Leader understood it
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This is how the
engineer designed it
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This is how the
programmer wrote it
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This is how the sales
executive described it
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This is how the project
was documented
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These are the installed
components
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This is how the
customer was billed
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This is how the
helpdesk supported it
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This is what the
customer really needed
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What computers cannot do
Not everything is quantifiable
Limitation on accuracy of representation
Approximation of the reality
Human behavior vs explicit rules
Advanced e-thinking: computer playing chess.
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What computers should not do
It should not:
Remove humans from the control loop
Replace human knowledge and experience
Take the human role
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Ethics and computing
Ethics in the context of ICT
Ethics and computing profession
The persuasive computer
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Review questions
How many layers the OSI model has ?
Name three layers of the OSI model
Give an example of hardware failure
Give an example of software failure implications
Provide three examples of what computers cannot do
Do you think that someday we will be able to
Humanize computers? Discuss.
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3- Your questions
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