arab open university - riyadh1 outline of unit 16: realistic expectations the digital computer, the...

Arab Open University - Riyadh 1

Outline of Unit 16: Realistic expectations

• 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 • What computers should not do• Ethics and computing

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The digital computer, the success of the twentieth centuryThe invisible computer.

In the same way that electric motors have disappeared from our

immediate awareness, computers – in the form of microprocessors

and their associated sensors, actuators and displays – are embedded

inside information appliances.

Interesting tools: the hand-held personal GPS navigators.

Massively Distributed Computing: The spare processing capacity of

relatively small personal computers, when combined appropriately

over a network, can be used to solve major problems.

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Moore’s law

• Gordon Moore, one of the founders of microprocessor manufacturer Intel and later its chairman, predicted in 1968 that he expected ‘a doubling of transistor density [...] every year’.

• Since Intel sold its first microprocessors in 1971, the semiconductor industry has managed to double the number of transistors on a chip roughly every 18 months, right up to the present time.

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Being driven to abstraction • Perhaps the most explicit example of abstraction and a

‘layered approach’ to managing complexity is the Open Systems Interconnection seven-layer model for handling the communication of information across networks.

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The OSI Model

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OSI model Layers

Layer 1. Physical Layer: Defines the physical

[hardware level] 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. The material about

OSI layers is additional (not from

M150).

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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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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.

OSI model Layers

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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.

OSI model Layers

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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.

OSI model Layers

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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.

OSI model Layers

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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.

OSI model Layers

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OutlineThe digital computer, the success of the

twentieth century• Reaction to the rise of ICT• What can go wrong with computer


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The responses of individualsThe optimists:

Respond in a wholly positive, enthusiastic way, seeing machines as freeing humans from drudgery as well as providing them with enhanced capabilities.

The pessimists:For them, any use of computers is potentially negative. They think that technology will increase power of surveillance of individuals by the state or other powerful organisations.

The realists: They are able to appreciate that the computer can act as a tool to enhance human activities but that it is limited in its potential by its (currently) digital nature and by our limitations in understanding our problems and ourselves.

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twentieth centuryReaction to the rise of ICT• What can go wrong with computer


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What can go wrong with computer applications?

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 with computer applications?

Inadequate models Over-maintained code: Every time changes are

made to a system they are likely to add to the complexity of the system, to introduce new errors, and to make subsequent maintenance more difficult.

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The Swing project

Inadequate requirements specification

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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twentieth centuryReaction to the rise of ICTWhat can go wrong with computer


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What computers cannot do

Not everything is quantifiable

Limitation on accuracy of representation

Models are only approximations to reality

Humans don’t work according to (explicit) rules

Advanced e-thinking: computer playing chess.

Can computers understand natural language?

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applications?What computers cannot do • What computers should not do• Ethics and computing

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What computers should not do

They should not:

Remove humans from the control loop

Replace human knowledge and experience

Take the human role

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applications?What computers cannot do What computers should not do• Ethics and computing

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Ethics and computingEthics in the context of ICT

‘Ten Commandments of Computer Ethics’

Terms of Service agreement

Ethics and computing professionprofessional morality: commitment to public well-being.

software development morality: commitment to ensuring quality in both process and product, arising from the adoption of ‘best practice’.

The persuasive computerThe Golden Rule of Persuasion: The creators of a

persuasive technology should never seek to persuade a person or persons of something they themselves would not consent to be persuaded to do.

arab open university - riyadh1 outline of unit 16: realistic expectations the digital computer, the...

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