M150 – DATA, COMPUTING and INFORMATION AOU Leb. - F08 - M150 - Unit 5 1 q Week 6 (Unit 5)

AOU Leb. - F08 - M150 - Unit 5 1

M150 – DATA, COMPUTING and INFORMATION

q

Week 6(Unit 5)

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M150 – DATA, COMPUTING and INFORMATIONWhat you should do this week?

Read Unit 5

Submit TMA01 before 16 November

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M150 – DATA, COMPUTING and INFORMATIONOutline

Unit 5

What’s next

Some review questions

Your questions

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Four Themes

Data storage: Logical and physical storage.

Data transmission: How the Internet works?

Large collections of data: Databases facilitate storage, access & data protection Metadata helps providing access to multimedia DB

Keeping data secure:Privacy issuesOwnership of dataRisks on data

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Persistent Data

To facilitate subsequent retrieval, you store your documents in some logical arrangement on a suitable storage medium for holding persistent data such as your computer’s hard disk.

The cabinet has several drawers and each drawer may hold a large number of files. In turn, each file contains a number of related documents. You label each drawer of the filing cabinet with a name, and you put a name tag on each file….

Now you have a strategy for retrieving your documents quickly.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Hierarchical or nested folder structure

The lowest level of the hierarchy documents This is called a hierarchical or nested folder structure,

because each folder may contain other folders

An Explorer window has two panes. The right-hand pane is a folder window (content can be displayed as icons or as a list)

The left-hand pane does not show any documents, but it does show hard disks, folders and any icon which holds other items (e.g. ‘network share’).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Tree Structure

With a bit of imagination, you can think of the folder structure loosely as a tree lying on its side. The desktop is the root of the tree, and each folder is a branch. The leaves of the tree correspond to documents.

Any similar hierarchical arrangement of objects is frequently called a tree structure or just a tree

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Path

How many doc./folders should you keep in a single folder? There is no limit !! Preferably do NOT exceed 20!

There are two distinct folders called ‘mail’ (prev. figure)

but no confusion arises because each is in a different place and has a different path leading to it.

A path contains the names of all the folders that lead to it from the root.

In effect a path allows you to identify unambiguously a folder or document and is often referred to as its full name or full path name (documents in the same folder must have different names)

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Search/Find function

Search function find items you have ‘lost’In Windows XP, the search will begin in ‘My Computer’ (or elsewhere by using the drop-down list).

Consider the Windows path name:C:\Projects\M150\Assignments\TMA02.doc‘C:’ is the root. ‘Projects’ is the name of a folder at the top level of the hard disk which contains a folder called ‘M150’ which in turn contains an ‘Assignments’ folder. The document ‘TMA02.doc’ is in the ‘Assignments’ folder.

Another place where you can see full path names is in a ‘Search Results’ window.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Directories

Each folder has a list, or directory, of the folders and documents that it contains (A folder is sometimes loosely referred to as a directory !!!)

Part of the directory for a given folder can be displayed on screen in a number of ways (alphabetically , in order of last modification date, size , type …) to aid human identification of the contents.

The directory of a folder also lists the address or physical location (more discussion to come!) on the disk of each document and subfolder in that folder. This address is internal to the operating system and cannot be seen in a user window.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Storage Technologies

There are various technologies of data storage:Storing data can be on the hard disk (typically is built into your computer) or on removable storage media such as CDs, DVDs, Zip disks, high-capacity tape cartridges…

There are various measures of storage size (Capacity):

PS: ‘kilo’ usually means 1,000 but in computing it denotes 1024 (210)

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Hard disk storage

Nowadays a typical PC comes with a 40/80 GB hard disk

The general principle of hard-disk storage: coated with a magnetic material that can be magnetised into a pattern representing a sequence of bits i.e the surface consists of millions of tiny magnets, which can each be magnetised in two possible directions representing 1 or 0.

A hard disk is 1 to 3 inches in diameter, and consists of one or more circular plates (aluminum, ceramic or glass…), each having two surfaces.

Data is recorded on each surface by magnetising a series of concentric circles called tracks.

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The disk surface is divided into a number of equal sized wedge-shaped regions called sectors. Within a sector each track holds the same amount of data – usually 512 bytes.

This is the basic unit of data handled by the disk control mechanism, and is called a block (each block of data is guaranteed to be the same size)Question: How can a sector hold the same amount of data on each track when the outer tracks are large than the inner tracks? (check answer on page 14)

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The actual reading from and writing to the disk surface is performed by a read/write head, which is attached to an arm that moves to and from the centre. The disk is kept spinning continuously, so each sector is under the head at some time.

The head hovers close to the spinning surface, which needs to be engineered carefully to avoid physical contact between the head and the surface (disk crash).

For each plate in a disk there are two read/write heads, one for each surface. In a read operation the head detects a magnetised pattern. In a write operation, the head magnetises the relevant pattern of bits on to the surface.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Hard disk storage The heads associated with all surfaces move in and out

together; at any one time they can read from the corresponding tracks on both surfaces of every plate in the disk. This set of tracks is called a cylinder (a disk may have 16000 cylinders i.e. each plate would have 16000 tracks on it).

Typical rotation speeds for hard disks are 5,000–15,000 revolutions per minute. A disk which rotates at 10,000 rev/min and has 60 sectors takes 0.1 millisecond (ms) for a 512-byte block of data to pass under the head.

On average it takes half a rotation (3ms) for the desired sector to reach the head – this is called the average latency. You also need to add to this the seek time (time taken for the head to move to the relevant track ~3–10ms)

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Removable storage media devices

Read/Write floppy disks: capacity limited to 1.4MB. Zip drive: 100MB or 250MB capacity Memory card: A removable medium which is very

popular (works on a principle that will not be discussed here).

Optical discs: CD (compact disc) DVD (digital versatile disc):

Store documents using a different technology based on the optical properties of the surface. The capacity of a CD is 650MB and data is stored on only one side of it in a single spiral groove which winds round the disc 22,188 times.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Optical discs

The data is packed uniformly along the groove, so that outer tracks of the groove hold more data than inner ones ( the disc spins more slowly when accessing data near the centre)

Conventional CDs are called CD-ROMs (Read-Only Memory), and have bits of data stored as ‘pits’ in their groove. Beams of laser light are used to burn the pits on the disc. A CD drive works by shining a low-power laser beam on the disc, which detects the presence or absence of a pit (the pits do not reflect the light).

DVDs (also called DVD-ROMs) pack the data more tightly, using smaller pits and a narrower groove which increase the capacity of a simple DVD to 4.7GB (Some DVDs use both sides having one or two layers each, yielding a theoretical maximum capacity of 19MB).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Hard disks vs. Optical disks

One important difference between CD/DVD-ROM discs and magnetic disks is the ability to write to them (once a pit has been burned, it cannot be erased).

There are two kinds of CDs:1. Recordable CDs, known as CD-R. Instead of burning

pits on the CD, the writing process dyes the relevant parts of the groove. When read by a CD drive these dye spots are indistinguishable from pits on a conventional CD. The process is not reversible.

2. Rewritable CDs, known as CD-RW, use a different technology altogether (heat a point on the disk to one of two temperatures corresponding to different states of the material). This process is reversible.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Labelling volumes

A hard disk or Zip disk or CD is called a volume.

Identifying a CD or other removable medium is necessary. It is important that each is given a label with a title. The volume can be stored in a rack with many similar looking ones but can be identified by its external label.

Besides its physical label a volume should also have an electronic label, which, for consistency, should be the same as the physical label. This electronic label is the name of the volume, and it will be displayed when you search the contents of your computer.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Sensible organisation of storage

Each volume contains a large number of documents, so there has to be a means of locating the one you want.

In the case of a magnetic disk three numbers are required to identify a block of data: cylinder number, surface number and sector number. This set of three numbers is called the address of the block.

To this end each volume has a volume table of contents or VTOC. The VTOC is a table with one line for each document.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Moving documents

What actually happens when you move a document ‘M150notes.doc’ from a folder (say ‘Current’) to another (say ‘Models’) on your hard disk?

Of course, you expect that from now on it will no longer be displayed in ‘Current’, but will appear when you inspect ‘Models’. What happens to the document itself, though? The simple answer is nothing. Moving a document between folders on a disk is really an illusion because the document does not move at all!

What really happens is something different. The document’s physical location remains unchanged, but the directories change (as illustrated in page 21).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Deleting documents

What actually happens when you delete a document? The operating system does not obey your instruction, but, instead moves the document to a special folder called ‘Recycle Bin’ or ‘Trash’ from which it can be retrieved.

When your hard disk is becoming too full – you can decide to ‘empty’ it. Once done, is there a hope for recovery?

When you moved documents to the recycle bin? They did not go anywhere; they remained in the same physical position on the disk. It was the directory entry for the document that was removed, with a new directory entry being created in the recycle bin.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Deleting documents

What you perceive when you navigate through the folders on your computer is not where the documents are located physically, but where they are located logically. That is, you are given a logical view of your documents which shows their relationship to each other in a hierarchical (nested) structure.

The operating system hides from you where items are located physically. The document does not need to be moved when you empty the bin but marked for deletion!!!!!!!!

So the document may remain on your disk for a long time without being overwritten. However, it is inaccessible since its directory entries have disappeared.

Specialized software can recover Privacy issue???

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Other storage media

Magnetic tape is a linear storage medium which is slow and difficult to access. So why would you want to use it?The main strengths of tape are its high capacity, its reusability and its cheapness.

A hologram is a three-dimensional image made with the aid of a laser which helps storing much higher volumes of data.

A Biological storage media idea is to represent 0s and 1s using two colour states of a suitable form of synthetic DNA. A number of such memory units would be attached to a support substrate to form a memory cell.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Computer networking

Networks of computers have been around for more than thirty years. In recent years, the internet has become a part of society, like the telephone, radio and television.

The web, which is based on the internet, has become the platform on which all kinds of information are disseminated. For example, it has generated e-commerce, new educational system …

Such applications, all of which use the internet, are creating novel forms of communication.

Besides the internet, many other computer networks exist (banks, Police, Travel agents and airline…).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Networking issues

A network of computers is linked together by communication links. These links may be: dedicated cable links; public telephone networks; radio or microwaves links.

Networks do not have to be dispersed over a wide area; their benefits are available locally. Any organisation using more than one computer is likely to have a local area network (LAN) to exploit the benefits of resource sharing.

Pocket-sized computers known as PDAs (personal digital assistants) can communicate with each other and with desktop computers using infra-red / Bluetooth signals. They form a small local network.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: The internet

The internet comprises a huge collection of computers (called hosts) with telecommunications links between them.

The internet has its roots in the American military-funded research community of the early 1970s. The first applications to use the internet were based purely on text.

The internet then began to be used for email and for file transfer. Modern graphical tools for accessing the internet (like Netscape Navigator) are much more recent dating back to the early 1990s.

How big is the internet? ARPANET was a network of just four computers. By 1996 that figure had grown to 15 million host computers, in 2002 it had multiplied ten times to 150 millions.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: The internet

The internet links together not just one type of computer but any type of computer running any operating system. By adopting the internet protocol each of these computers can become an internet host.

The telephone system (which uses analogue signals consisting of a continuously varying voltage) was designed for voice transmission.

As your computer communicates using digital signals (consisting of discrete bit patterns), a modem (modulator-demodulator) which is a piece of equipment will be sitting between your computer and the telephone socket.

The modem converts the data signals from the computer into analogue signals, a modem at the other end will convert the signal back into digital.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Browsing the web

In 1990, Tim Berners-Lee at CERN created the forerunner of the web which today is a collection of hypertext documents distributed worldwide and linked by the internet.

The value of the web is that trillions of pages of web content are linked together via multiple hyperlinks.

As you have learned in previous units:

the software you use on your computer to access and view documents on the web is called a web browser;

the basic unit of web content is the web page which is an HTML document.

The browser accesses the page, held on a remote computer (web server), and downloads it to your computer (the client).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Internet addressing

The address has several levels to it (like the posting system):

At the highest level: domain (a collection of internet hosts). Two types of top-level

codes of three letters

codes with two-letter (normally countries)

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Country code domains are usually subdivided ac.uk (academic community), co.uk (commercial), gov.uk (national and local government)

Many individual domain names are available within each top-level domain. Within ac.uk there is open.ac.uk, the OU domain (the central address for the OU on the internet)

Once the domain name open.ac.uk has been approved by an external agency, the OU is free to allocate subdomains and host names within this naming scheme.

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How addressing down to the document level?The address associated with a hyperlink is given in the form of a URI (uniform resource indicator), which specifies the service requested and the full address of the document.

An example of a URI:http://mcs.open.ac.uk/mcsexternal/courses/m150.htm http:// identifies the protocol (HTTP) mcs.open.ac.uk’, specifies the server. The host

address is in two parts:1) ‘mcs’ , which identifies a particular computer2) ‘open.ac.uk’, which identifies its domain.

The rest of the address is the path within ‘mcs’ that leads to the required document.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Naming hosts

It is usually convenient to assign a name to each computer on a network so that users can identify it easily. In a large network it is common to use a systematic naming scheme.

A typical naming system might use names like ‘anemone’ or ‘buttercup’. These hosts in the OU domain would then be known to the internet as ‘anemone.open.ac.uk’ and ‘buttercup.open.ac.uk’

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: IP numbers

The naming scheme (convenient for humans) is not actually used by the messages that travel across the internet. Instead each host has a 4-byte number associated with it, called its IP (internet protocol) number.

The IP number carried by a message ensures that it reaches the correct destination. How does the message discover the IP number of its destination host? Answer is that special directories, called domain name servers, keep this infor.

The first thing that happens when a URI is executed is that the host name is sent to a domain name server to be resolved (new hosts are being added so domain name servers need to be kept up to date).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Logical and physical names

Suppose that your website on ‘orchid.open.ac.uk’ has crashed. And you acquired an up to-date computer which you name ‘peony.open.ac.uk’ and move your website there.

Problem: Now no one can find your web pages any more, as they are no longer at the same address.

A good solution is to avoid reliance on named physical machines. The way to do this is to identify the web server to the internet not by the name of the physical computer it resides on, but by a logical name.

This means that an index must be kept which associates the logical name of a server with its current physical host.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Email

Very popular use of computer networking: Email

A mail application, or mail client, combines high speed with apermanent record. Email is asynchronous

Email combines immediacy and permanent record

Organisations can have their own internal email system that is independent of the internet

Email achieves its universality by using text messages comprising ASCII-coded text only. Unlike other URIs, an email address identifies a user: [email protected]

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The internet works using a standard protocol. You despatch an email message and expect it to arrive. You do not know which route it took or which countries it passed through.

When data travels across the internet, it is broken up into units of a standard size called packets. Each packet carries the address information so that it will reach its intended destination. The packets are re-assembled into a single item on arrival.

Along with the actual data, an email also carries transmission information in a number of lines, called headers.

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Email address of the recipient Date and time of despatch. Subject of the message ‘Reply-to’ field gives the reply

address of the sender

Headers whose names begin with ‘X-’ are are used to convey additional information. The header X-Mailer reveals that the message was composed using version 4.01 of the Pegasus

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Sending attachments

Email transmission is restricted to text but how is it possible to attach documents of any kind to an email message?Ans: By encoding the attached file as a series of alphabetic characters and appending them to the end of the message. (An arbitrary attachment can be converted into ASCII code)

In order to enable the receiving mail client to decode the

attachment, the encoding scheme must conform to a standard. One of the internet standard for encoding mail attachments is MIME (Multipurpose Internet Mail Extensions)

Content-type: text/plain indicates the nature of data and will usually be followed by ‘charset=iso-8859-1’ for English text

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: How does data travel?

The transmission medium could be a wire carrying electrical signals or an optical fibre carrying light signals. Wireless connection could be infra-red, radio or microwave link.

Communication takes place in the form of serial transmission Protocols are needed to ensure that, on arrival, the receiving

computer interprets the stream of bits with its original meaning.

The receiver need to know when the transmission begins. A simple protocol is to include start & stop bits with each byte

If something has gone wrong, the receiver sends a simple message to the transmitter indicating a failed transmission.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Databases

A database (db) is a collection of data stored in a computer system according to a set of rules, and organised to facilitate access involving complex searches and selection.

The primary emphasis of database applications is on making the data persistent, and structuring it so as to minimise redundancy, avoid inconsistency & maximise the usefulness of the data for the purposes of access and updating.

A query (request to db) is used to get specific information from the db. The response to the query ideally extracts from the database all the relevant information. So a database is part of an information system.

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Key ???

What is the engine size of Tom Cobbley’s car?(Hint: use the two tables in combination)

Table ???Row ???Field ???

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Databases consist of many tables holding vast amounts of data, designed with great care in order to be able to provide answers to (possibly complex) queries.

A typical industrial database system will consist of: A collection of tables Data (called metadata) which describes the tables

(what each column in a table means, and how many tables there are in a database….)

Facilities for backing up the tables. Facilities for ensuring security (credit card details) A query facility.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Object database

Object database may contain video, voice and music along with more traditional forms of data.

A data object (sound, image, video) may be contained within a database as ‘an object in a box’. The box has a name and the database can access the object using this name.

An object stored in this way is called a BLOB (binary large object). There are facilities for the storage and retrieval of these data types but the weakness of this approach is that you can NOT query the content of a BLOB (the BLOB has NO structure to it).

Solution: Metadata

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Metadata

In order to describe anything other than the simplest of data, it is necessary to provide some form of explanatory data (i.e. metadata) about the data. Email headers are good examples.

Web pages have a rudimentary form of metadata in the form of keywords that can be used by search engines to locate web pages of a particular topic.

Each item in the <HEAD> section of an HTML document is an example of metadata. It is not part of the content of the document; rather, it says something about the content.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Metadata

An adequate collection of metadata (hooks or pointers) will identify the various features of multimedia databases to make it searchable.

Each still picture, audio clip and video will have a number of associated items of metadata.

MPEG-7 provided a visual descriptors (colour, texture, shape, position, motion and face recognition) and audio descriptors (key, mood, tempo and tempo changes).Example: This is a scene with a barking brown dog on theleft and a blue ball on the right, with the sound of passingcars in the background.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Privacy

Privacy – keeping some things removed from general or public knowledge – is central to our way of thinking.

There is a lot of data about us in a semi-public domain that we may not even be aware of (loyalty card at a supermarket allow to track all your purchases!).

Computer systems provide the facility for government, local authority, tax authorities, your bank … to have control over vast, and detailed, amounts of data about you. They can store it for indefinite periods and use it in a variety of ways.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Data and the law

Data protection or data access legislation may vary from jurisdiction to jurisdiction, and depends on the willingness of the relevant authorities to enforce it, and of most individuals and organisations to adhere to it.

Data protection laws in any jurisdiction are likely to have some or all of the following characteristics: a legal definition of data (limited to electronic forms or

also covers handwritten and typed data, photographs..); a description of how data may be acquired lawfully; what uses the data may be put to; any time limits on storage; who may lawfully access and use the data, and for what.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Computer ethics

Ethics is defined as a set of moral principles that should guide our acts as a citizen. 1) Thou shalt not use a computer to harm other people.2) Thou shalt not interfere with other people’s computer work.3) Thou shalt not snoop around in other people’s computer files.4) Thou shalt not use a computer to steal.5) Thou shalt not use a computer to bear false witness.6) Thou shalt not copy or use software for which you have not paid.7) Thou shalt not use other people’s computer resources without

authorisation or proper compensation.8) Thou shalt not appropriate other people’s intellectual output.9) Thou shalt think about the social consequences of the program

you are writing or the system you are designing.10) Thou shalt always use a computer in ways that ensure

consideration and respect for your fellow humans.

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Linking and theft

Web pages often contain links to web pages developed by other users (gateways).

Consider a site which sets itself up as an internet newspaper and contains links to individual stories stored at other online newspaper sites. What should the ethical position be on this?

It could be regarded as an example of intellectual property theft.

It could be argued that the material has not been stolen because the text has not been cut and pasted but simply linked to!!!

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Security

Legislation to protect data, and in particular computerised data, is desirable. However, the law itself is never sufficient.(You never leave your home open when you go out!!)

Once you link your computer to the internet, you need to think about ways of making it less accessible to unwanted visitors who, in computer jargon, are termed hackers.

One solution is to allow access using a password only. It may be desirable to secure a whole network of computers from unauthorised outside access by using a firewall (a software system which controls data traffic entering and leaving the network).

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Ownership and rights over data

The concept of data ownership is legally very unclear in most countries. Who actually ‘owns’ medical records?? (Patients, Doctors, pharmacists or health departments)

Intellectual Property Rights (IPR): the right to gain financially from the products one creates

Moral rights: the right to say how one’s products can be used (the content of letters that you write, and even the content of assignments that you prepare …)

Copyright laws: afford some sort of protection for intellectual property (databases are subject to copyright)

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M150 – DATA, COMPUTING and INFORMATIONUnit 5: Worm, Viruses and Trojan horses

A worm is a program intended to subvert a whole network of computers. It transfers copies of itself to other machines on the network.

A virus is a program designed to cause specific damage to your software by attaching itself to documents. Ex: deleting important documents from your hard disk.

A Trojan horse is a code which looks legitimate but attempts to do something quite different (modify documents on your hard disk, collect passwords…). Typically the name of the document will be misleading.

Anti-virus softwares will protect your system but needs regular updates because new viruses appear on a daily basis.

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M150 – DATA, COMPUTING and INFORMATIONWhat’s next

Unit 6: The structure of hardware and software

Hardware, software and computer systems The resources of a computer, and how they are

managed Running a program Types of programming language The structure of computer programs

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M150 – DATA, COMPUTING and INFORMATIONSome review questions

How can you locate a previously saved document in order to open it? What is the name of the document in C:\My Documents\

MyHomePage.htm and where would you expect to find it? How can a sector hold the same amount of data on each track, when

the outer tracks are large than the inner tracks? At what stage is a document deleted physically from a disk? What resources do you think can be shared across a LAN? What is a hyperlink? What does the part of the email address following @ symbol

represent? Identify a difference between telephone and radio communication. What characterises data as persistent? How can metadata help locate specific content in a multimedia db? What is the main aim of data-protection legislation? What security advantage do read-only media have over read/write

media?

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M150 – DATA, COMPUTING and INFORMATIONYour questions

?