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Web Programming & Scripting

State some types of transmission media: Copper wires (Coaxial & Twisted Pair), Fibre Optic, Radio & Satellites.
How is data transmitted over short distances? Small, discrete changes in electrical current.
How does a Local Area Network (LAN) work? It uses dedicated links between computers, with the computers themselves co-ordinating access.
What are the 3 common network topologies? Bus, Star and Ring.
How do computers share Ethernet? Data is divided into small chunks known as packets, each packet propagates to either end of the cable until it reaches it's destination. It is ignored by all other computers.
What is Carrier Sense Multiple Access (CSMA)? The electrical activity that occurs during packet transmission is known as the carrier. Before a computer sends a packet, it checks the network for a carrier, and will only transmit if the network is quiet.
What is collision detection? The transmitting computer monitors the network to check for interference. The system is collectively known as CSMA/CD.
What happens in the event of a collision? Both computers wait a random amount of time before re-sending the data. This maximum random time is doubled for each subsequent collision.
Why do discrete voltage changes not work when sending information over long distances? The signal attenuates to zero due to the resistance in the wire.
How is data sent over long distances instead? A continually oscillating wave. (Sine). Bits of data are modulated on to the wave at the transmitting end, and demodulated off at the receiving end.
What piece of hardware is required for successful long distance communication using continually oscillating waves? A MODEM. Modulator/Demodulator.
Define Bandwidth: The number of signals per second that a medium can accommodate.
Define Multiplexing: Several logical connections share a single physical connection.
Define Broadband: A transmission method which supports a relatively wide range of frequencies which may be divided into channels.
Describe "Thick" ethernet: Computers are connected to the thick ethernet cable via transceivers.
Describe "Thin" ethernet: Computers are connected directly to the thin ethernet cable using a BNC (a type of connector).
Describe twister pair ethernet: Physically it's a star, all computers are connected to a central hub. However logically it is a bus as the hub does not provide any central co-ordination, it simply simulates the action of a share cable.
How does a Dial-Up Modem send information? It sends the information over the voice telephone system.
Describe Digital Subscriber Line (DSL): Uses the two wire local loop from the local telephone exchange to homes, using the entire bandwidth. Discrete Multitone (DMT) divides the data into 247 channels. It makes use of the fact normal telephone lines are limited to the frequency of human voices.
Describe a Cable Connection: Modems deliver the computer data using the coaxial cable of the local tv company, using frequencies not dedicated to the delivery of tv channels.
Why are network protocols required? Communication hardware transfers a stream of bits. However, usually much more sophisticated instructions need to be transmitted, and software is required to provide interoperability, by maintaining standards.
Describe the protocol layered model: Protocol software on each computer is divided into modules - each corresponding with a layer. The collective protocols on a computer are known as a stack.
What is required, in terms of protocols, to allow network communication? The same protocol stack needs to be installed on all computers in the network, regardless of hardware or operating system.
Explain how TCP/IP help create the internet: Modems connect different networks, and translate between different frames and addressing schemes. IP creates the illusion that there is only one network, and provides a uniform addressing scheme. It also defines a universal virtual packet.
Describe the purpose of the IP protocol: It is a connectionless packet switching protocol. It defines a universal virtual packet - the IP datagram, and routes packets of data between nodes along a previously un-established path. It is responsible for forwarding packets based on their address.
Describe the purpose of the TCP protocol: Data may be sent in a continual stream of bits between hosts, TCP is responsible for verifying the correct delivery of data between machines.
Define Host: Any system that connects to an internet and runs an application.
What is a Router? A device that connects independant networks together to form an internetwork.
What is an IP number? All hosts on the internet must have a unique identifying number.
What are Domain Names and how are the assigned? They are labels assigned to IP numbers, they are retrieved from Domain NameServers (DNS).
IPv4 consists of 4 bytes, or 32 bits. What are the two parts that these are divided into? Prefix - The physical network to which the host is attached. Suffix - A host attached to a given physical network.
What notation does a IPv6 address use? Hexadecimal notation, it uses 128 bits for the addresses.
What is the hierarchy of domain names? Top level (Country/Category), Second level (Organisation), Third level (Subnet)
Domain names must be converted before communication can take place, how is this done? The client queries the Name Sever for the IP, which is then used to communication with the web sever and retrieve the specific page.
Describe the Client-Server Paradigm: The server application waits passively for content from clients. The client application actively initiates contact with the sever. Information travels in both directions.
What do web servers in an operating system do? They provide responses to browser requests, using HTTP. They are a back ground process, and monitor the communication port, awaiting HTTP requests.
What are Multipurpose Internet Mail Extensions (MIME) used for? Specifying document types transmitted over the web. (e.g. .html). Some types cause the server to send helper applications or plug-ins.
Describe the exchange between a web browser and a sever to retrieve a document and display it in the browser: Client establishes a connection to the server and sends a HTTP request. This consists of a request line, header files and an optional message body. The server responds generating a HTTP response. Containing a status line, header fields and response body.
Explain what HTML is: A mark-up language, it describes the general form and layout of documents to be displayed by web browsers.
What is HTTP, and what does it being a stateless protocol mean? Application level, client-server protocol. It is small, fast and easy to implement. Requests are not related, they are independent of each other.
What are the advantages of HTTP being a stateless protocol? Simplifies server design - no storage is required.
What are the disadvantages of HTTP being a stateless protocol? More information must be included in each request.
What are the two main directories on a web server? Server root, and a document root (with the user document root directory within this)
What is a virtual document tree? Part of the servable document collection stored outside the document root,
What is virtual hosting? Support for more than one site on a computer.
What is a proxy server? Serve documents that are in the document root of other machines.
What should the file name of a websites home page be? index.html
The opening and closing tags of an element act as a what, for the content they enclose? A container.
How are comments written in HTML? <!--
What are the differences between HTML and XHTML? HTML has lax syntax rules, leading to sloppy and ambiguous documents. XHTML has a much stricter syntax, leading to clean and clear documents in a standard form.
Nested lists can be nested in any type of list, however what must they be contained within? A list item.
What are HTML frames? Rectangular sections of the display window, each of which can display a different document.
What are the uses of HTML frames? Navigation systems, static title and advertising.
Why is the use of frames discouraged? The page is the basic unit of the web, and is represented by a URL. As frames allow more than one page to be shown at once, it breaks the fundamental paradigm of the web. It also causes usability issues.
What do style sheets allow you to do? Impose a standard style on a whole document, or a collection of documents.
What is an inline style? Specified for a specific occurrence of a tag, and only that tag.
What is a document level style? These apply to the whole document in which they appear, and are positioned in the <head> tag.
What is an external style? These can be applied to any number of documents, and are in a separate .css file.
What is the cascade hierarchy? Individual element - Web page - CSS file - Internet browser
What are pseudo classes? These styles happen when an event occurs rather than because the target element simply exists.
JavaScript is dynamically typed, what does this mean? Any variable can be used for anything, the interpreter determines the type of a particular occurrence of a variable.
JavaScript is interpreted, what does this mean? The source code is embedded within HTML documents, there is no compilation.
Why is JavaScript useful? It transfers some of the load from the server to the client. It also allows user interaction via the use of forms.
Describe JavaScript execution: It is executed entirely by the browser, once it is downloaded, the server is not involved (although JS can be used to issue HTTP requests). It does not require the Java VM, so is relatively fast.
What is the difference between Java and JavaScript? JavaScript is not object orientated, rather object based. JavaScript does not support polymorphism or class-based inheritance.
How is content dynamically changed on-screen using JavaScript? The Document object has a method, write, which allows content to be dynamically created. document.write("Hello <br>");
Describe an alert box: A dialogue box which displays a string, and an OK button.
Describe a confirmation box: A dialogue box that displays a parameter, an OK and a CANCEL button.
Describe a prompt box: A dialogue box with a string, a text box and OK and CANCEL buttons.
What is the Document Object Model? An abstract model that defines the interface between HTML documents and application programs - an API.
What are the four ways that HTML documents can be referenced? id, tag name, class name, HTML object collections.
Define Event: A notification that something specific has occurred, either within the browser or an action of the user.
Define Event Handler: A script that is implicitly executed in response to the appearance of an event.
What is dynamic HTML? A HTML document whose tag attributed, tag contents or element style properties can be changed after and whilst it is still being displayed by the browser.
What must the home page of a website contain? The purpose of the site, site content, and how to find the content in the site.
What must the web designer think about optimising when using Graphics and Text in a website? Storage and page loading times.
What user disabilities must the creator make the website suitable for? Visual, motor, cognitive, auditory impairments and seizures.
What does the Disability Discrimination Act (1995) mean for web designers? It makes it illegal to discriminate against people with disabilities. It applies to anyone providing a service.
Give examples of some assistive technologies: Speech recognition, screen magnification, keyboard overlays, screen reader software and braille keyboard.
What is the first principle of the Web Content Accessibility guidelines (WCAG)? Perceivable. Information and user interface components must be presentable to users in ways they can perceive. Text alternatives, alternatives for time-based media, adaptable and distinguishable.
What is the second principle of the WCAG? Operable. User Interface and components must be operable. Keyboard accessible, enough time, seizures and navigable.
What is the third principle of the WCAG? Understandable. Information and operation of the UI must be understandable. Readable, predictable and input assistance.
What is the fourth and final principle of the WCAG? Robust. Content must be robust enough that it can be interpreted reliably by a wide variety of user ages, including assistive technologies. Compatible.
What are some examples of server side applications: Search systems, document management systems, user administration, transactions and e-commerce.
What is a cookie? A name and value pair that is passed between a browser and a server in the HTTP header.
What do cookies allow? Targeted advertising and shopping baskets.
Define session: The time span during which a browser interacts with a particular server.
Describe XML: A meta-markup language. It is used to create new markup languages for particular purposes. (It was used to define XHTML).
What is an XML based mark-up language called? A tag-set, or an XML application.
What is an XML processor? A program that parses XML documents and provides the parts to an application.
What do XML documents consist of? Data elements, mark-up declarations and processing instructions.
What is the XML declaration needed at the beginning of an XML document? <?xml version = "1.0" encoding = "utf-8"?>
What is the better alternative to attributes in XML, and why is is better? Define a new nested tag to provide more info about the content of a tag. These are better as they are able to describe structure more efficiently that attributes.
What are the two auxiliary files associated with XML files? One to specify the structural syntactic rule, and one to provide a style specification.
What are the reasons for the entity structure of XML documents? Makes larger documents easier to manage, repeated entities need not literally be repeated, binary entities can only be referenced in the document entities.
What are Document Type Definitions? A set of structural rules called declarations. They specify a set of elements, along with how and where they appear in a document. They provide a standard form for a collection of XML documents and define a mark-up language for them.
What do XML parsers do? Check for well 'formedness'. Some check validity, relative to a give DTD.
What does AJAX stand for? Asynchronous Javascript And XML.
What is AJAX used for? It is a technique for creating fast and dynamic web pages. It allows web pages to be updated asynchronously, by exchanging small amounts of data with the sever behind the scenes.
What type of applications benefit from AJAX, and give some examples: Those that have frequent interactions between the client and the server. e.g. google maps, Gmail, YouTube.
How does AJAX work? Browser creates a XMLHttpRequest, and sends it to the server through the internet. This processes the request and creates a response. This is sent to the browser via the internet, and the page content is updated.
Describe the request phase of an AJAX application: Communication with the server is made using the XMLHttpRequest object. When the server receives the request, it sends a sequence of notices called callbacks to the browser. The value of the input is then sent.
Describe the receiver phase of an AJAX application: The server response is fetched.
Why is a shared data channel such as those used in LAN, not suitable for long distance communication? With shared data channels, computers must co-ordinate their access. This is not suitable for WAN as delays will inhibit co-ordination.
How does the CSMA/CD protocol deal with collisions on an Ethernet network? Each computer senses for garbled transmission - a collision. After a collision is detected, computers wait a random time, up to a specified maximum before re-sending. The maximum is doubled for each subsequent collision.
What is a modem? Hardware that takes bits and applies modulation, and hardware that extracts bits from a modulated wave. A modem combines these, allowing full duplex communication.
Describe the purpose of the IP protocol: IP is a connectionless packet switching protocol. It defines a universal virtual packet - the IP datagram. It routes packets of data between nodes along a previously un-established path. It forwards packets based on their four byte destination address.
Describe the Ethernet address (Media Access Control, MAC) addressing scheme: A unique number built into each ethernet system by the manufacturer.
Describe the Internet Address (IP Number) addressing scheme: A unique identifying number for each host on the internet. It is 32 bits, but is usually displayed as four bytes separated by dots.
Describe the Hose Name addressing scheme: All hosts must have a unique name. This may be a single word, or follow a hierarchy.
What are the different parts of this HTTP response message? HTTP/1.1 200 OK HTTP/1.1 - The protocol version 200 - Status code OK - "Reason phrase" - explains the status code.
Explain what XML is: It is a meta-markup language. It is used to create new markup languages for particular purposes.
Explain what a Cascading Style Sheet (CSS) is: A w3c specification which provides the means to control the presentation of XHTML documents. They allow a standard style to be imposed on a whole document or collection of documents.
List three of Jacob Nielsen's "Top 10 worst mistakes of web design": Bad Search engine, PDF files for online reading and not changing the colour of visited links.
How is JavaScript embedded in an XHTML document? <script type = "text/javascript" > ....... </script>
Explain what the Document Object Model is: A specification for dealing with HTML/XHTML documents from JS by describing and providing access to their structure. It is an API.
Explain the difference between client side and server side scripting: Client side scripts are executed by the browser (the script is sent to the client by the server). Server side scripts are executed by the web server (the client never sees the script).
Explain what Java Servlets are: A compiled Java class executed on the server system under the control of the web sever. It is called through XHTML. They receive requests and return responses, both of which are supported by the HTTP protocol.
Why is it useful for the server to be able to relate a HTTP request to a session? It allows the implementation of: shopping carts for multiple simultaneous customers, customer profiling for advertising and custom layouts for various users.
How does PHP implement session tracking? PHP creates and maintains a session tracking ID, which is created with a call to "session_start" with no parameters. Subsequent calls retrieve any session variables that were previously registered in the session.
Created by: Sparksy