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Web Technology > Exam Prep > Flashcards

Exam Prep Flashcards

1
Q

History: the internet started in… ?

A

the 60s

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2
Q

What is IP?

A

IP is the fundamental protocol defining the Internet

Communication protocol: how computers talk - Transfer data packets from source to destination
host. If destination is unknown (e.g. host is in another
LAN), packet is sent to a gateway that connects to
more than one network

32-bit number (in IPv4)

Limitations of IP:
– No guarantee of packet delivery (packets can be
dropped without reporting an error)
– Communication is one-way (source to destination)

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3
Q

What is TCP?

A

Transmission Control Protocol - Vinton Cerf et al. wrote 1st TCP spec in 1974

TCP adds the notion of a connection,
implemented on top of IP
– Provides guarantee that packets delivered
– Provide two-way (full duplex) communication
– More like telephone than postal network

also adds concept of a port
– TCP header contains port number representing an
application program on the destination computer
– Some port numbers have standard meanings

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4
Q

what is UDP?

A

User Datagram Protocol

– Builds on IP
– Provides port concept
– No connection concept
– No transmission guarantee

Advantage of UDP vs. TCP:
– Lightweight, so faster for one-time messages

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5
Q

What is DNS?

A

Domain Name Service - the “phone book” for the Internet

Map between host names and IP addresses

DNS often uses UDP for communication

Labels separated by dots, e.g., www.example.org

Final label is top-level domain

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6
Q

what is FTP?

A

communication between ftp client and ftp server for interactive file
transfer

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7
Q

what is HTTP

A

communication between web client (browser) and web server for file
transfer on the web

Normally implemented over a TCP connection

URL schemes are http,
https, ftp, mailto, and file

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8
Q

what is World Wide Web?

A

Invented at CERN in 1989 by a software
engineer named Tim Berners-Lee

Distinctive feature of Web: support for hypertext
(text containing links)
– Locating documents using Uniform Resource
Locators (URL)
– Document representation using Hypertext Markup
Language (HTML, lecture 2,3)
– Communication via Hypertext Transport Protocol
(HTTP, 4)

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9
Q

what is a URI?

A

Uniform Resource Identifier

two types:
- Uniform Resource Name: Can be used to identify resources with unique names,
such as books (which have unique ISBN’s)
- Uniform Resource Locator: Specifies location at which a resource can be found

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10
Q

who invented html? when? how many tags did it have vs now?

A

Tim Berners-Lee, a physicist at the CERN research institute in Switzerland invented HTML in 1991. This first version consisted of 18 HTML tags. Now, there are currently about 140 HTML tags, although not all of them are supported by modern browsers.

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11
Q

what are some key advantages and disadvantages of JavaScript?

A

adv: speed, simplicity, popularity, interoperability, server load, rich interfaces, extended functionality, versatility, updates
dis: client-side security and browser support

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12
Q

what are typical examples of JavaScript usage

A

web development/applications, presentations, server applications, web servers, games, art, smartwatch/mobile applications, flying robots

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13
Q

what is DOM?

A

When writing web pages and apps, one of the most common things you’ll want to do is manipulate the document structure in some way.

This is usually done by using the Document Object Model (DOM), a set of APIs for controlling HTML and styling information that makes heavy use of the Document object.

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14
Q

what are events + event handlers + host objects?

A

JavaScript lets you execute code when events are detected. HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.

JavaScript event handlers designed to process events such as those listed above, with the object(s) that can support each event

Host objects are supplied by other environment through a connection. The Host Objects are can not be same always because of the environment. Any object which is not native is a host object, basically Host Objects are provided by the browser environment

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15
Q

what are the main differences between JavaScript and languages such as Python or C++

A

Python is a better-designed language that makes it easy to maintain, whereas JavaScript is poor.

Python is not good for mobile development, whereas Java-Script is good.

Python is slow to run compared to JavaScript.

Python provides a huge standard library, whereas JavaScript has a limited standard library.

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16
Q

underlying concepts of development, testing and debugging of JavaScript code

A

JavaScript development tools have been slow to materialize, but there are various options available today.

The Chrome Developer Tools are a quick way to debug your JavaScript code.

Visual Studio Code includes built-in JavaScript IntelliSense, debugging, formatting, code navigation, refactorings, and many other advanced language features.

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17
Q

key advantages and disadvantages of AJAX technology

A

adv: reduce server traffic and increase speed, Enable asynchronous calls, XMLHttpRequest, Reduce bandwidth usage, Form Validation
dis: Open-source, Search Engines cannot index Ajax pages, difficulties for your web pages to debug as well as make them prone to possible security issues in the future, considerable dependency on JavaScript, challenging to bookmark a specific state of the application

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18
Q

typical examples of AJAX usage

A

Create a XMLHttpRequest with a callback function, and retrieve data from a TXT file.

Request Header Information

Retrieve Server Data with PHP and ASP

Retrieve Database Information

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19
Q

what is JSON data

A

Java Script Object Notation.

JSON is a lightweight format for storing and transporting data.

JSON is often used when data is sent from a server to a web page.

JSON is “self-describing” and easy to understand.

values must be one of the following data types: a string. a number. an object (JSON object) an array. a boolean. null. JSON values cannot be one of the following data types: a function.

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20
Q

the notion of a Client/Server Model

A

In many network applications, the roles of the
two pieces of software communicating over
the network is really different:
• One piece of software always takes the initiative,
and is called the client
• A second piece of software is always reactive,
and is called the serve

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21
Q

HTTP requests & response messages

A

Request-response protocol in the client-server computing model

Client submits an HTTP request message to the
server

Server typically provides resources such as
HTML files and other content

Response contains completion status
information

22
Q

what is IRI

A 
• Internationalized Resource Identifier
• Modern form of URI
• Is a generalized form of URI
– URI allows only ASCII characters
– IRI allows use of Unicode
23
Q

common http request methods

A

• GET
– Used if link is clicked or address typed in
browser
– No body in request with GET method
• POST
– Used when submit button is clicked on a form
– Form information contained in body of request
• HEAD
– Requests that only header fields (no body) be
returned

24
Q

HTTP request:

sample header fields

A

• Host
– host name from requested URL (required)
• User-Agent
– e.g. type of browser sending the request
• Accept
– Acceptable MIME types and encoding for responses
• Connection
– value close tells server to close connection or not
• Content-Type
– MIME type of POST body, if applicable
• Content-Length
– bytes in body
• Referer
– URL of document containing link that resulted in this request

25
Q

what are MIME types?

A 
• Standard identifier used to indicate the 
type of data that a file contains
– used for Web data, email attachments, …
• IANA manages the official registry of
media types
• Format of MIME types: type/subtype
– text/html
– image/png
– video/mp4
26
Q

HTTP response:

status codes?

A 
• Three-digit number
• First digit is class of the status code:
1=Informational
2=Success
3=Redirection (alternate URL is supplied)
4=Client Error
5=Server Error
• Other two digits provide additional 
information

200 The request was succesful. The client can read the result of the request in the body and the headers of the response.
201 The request succeeded, and a new resource was created as a result.
400 The server could not understand the request due to invalid syntax.
401 Bad or expired token. This can happen if the user revoked a token or the access token has expired. You should re-authenticate the user.
403 The web browser does not have permission.
404 The server can not find the requested resource. In an API, this can also mean that the endpoint is valid but the resource itself does not exist.
500 The server has encountered a situation it does not know how to handle.

27
Q

Virtual Hosts?

A

hosting multiple web sites on a single server

28
Q

Principles of REST network architectures?

A
  1. All pieces of information are resources that are uniquely addressable using a URI
  2. Both client and server do not need to be aware of intermediate proxies or caches nor how the server generates/client renders the representation of the resource
  3. There is no communication state (stateless)

simplifies global design and improves performance but sometimes makes server programming more difficult

29
Q

what are safe and idempotent HTTP methods?

A

HTTP GET method should be safe: no side-effects

Other methods than GET and POST should be idempotent: requesting the same
resource multiple times will yield the same result and no further
side effects as a single request

30
Q

web “cookies” and how they relate to HTTP state

A

HTTP cookies (also called web cookies, Internet cookies, browser cookies, or simply cookies) are small blocks of data created by a web server while a user is browsing a website and placed on the user’s computer or other device by the user’s web browser.

Cookies are placed on the device used to access a website, and more than one cookie may be placed on a user’s device during a session.

31
Q

Same origin policy VS cross origin resource sharing

A

Site A provides AJAX web services to support Web pages from site A
– But: does not want a script on a page from site B to also make calls to site A
– Users might have used site A before, and site B might be trying to steal
information from site A about the user
– But requests to A come from the client, and A doesn’t know if the client is
running a script from A or B!
– Only the browser knows it is running a script from B calling A
– So the browser will block calls to A on pages from B (except when A opts in
explicitly: CORS)

Was considered safe before AJAX
– HTML from site B often uses resources from A:
• GET: Images, CSS style sheets, JavaScript libraries
• POST: form submissions
– Harder to abuse than in the AJAX case
• E.g. requesting privacy sensitive data
• Opt-in policy using CORS http headers

32
Q

Common Log Format?

A

standardized text file format used by web servers when generating server log files. Because the format is standardized, the files can be readily analyzed by a variety of web analysis programs,

Each line in a file stored in the Common Log Format has the following syntax:

host ident author date request status bytes

33
Q

explain the difference between an information need and a search query

A

information need is the topic about which the user desires to know more, and is differentiated from a query, which is what the user conveys to the computer in an attempt to communicate the information need.

34
Q

define the notion of relevance in this context

A

relevant if it is one that the user perceives as containing information of value
with respect to their personal information need.

Our example above was
rather artificial in that the information need was defined in terms of particular words, whereas usually a user is interested in a topic like “pipeline
leaks” and would like to find relevant documents regardless of whether they
precisely use those words or express the concept with other words such as pipeline rupture

35
Q

define the evaluations metrics precision and recall in relation to the notion of relevance

A

Precision: What fraction of the returned results are relevant to the information need?

Recall: What fraction of the relevant documents in the collection were returned by the system?

36
Q

define the notion of precision at N

A

When the number of results grows larger, it

might not be relevant what the precision over the entire set is, but only first N results

37
Q

describe the advantage of ranking based

on tf.idf scores over ranking based on raw term counts

A

Ranking - State of the art search
engines use all kinds of
tricks for ranking

Example weighting scheme: tf.idf

Every word is assigned a weight for a document.
Some words are more important than others.

38
Q

explain how Zipf’s law and Heaps’ law related to word frequencies in natural text

A

Zipf’s law - The most frequent word will occur approximately twice as often as the second most frequent
word, three times as often as the third most frequent word, etc.
Formally: the frequency of a word is inversely proportional to its rank in the frequency table.

Heaps’ Law - By scanning the text we will hit upon the most
common words rather quickly, but we will,
(increasingly slower), continue to encounter
(infrequent) new words

39
Q

explain what a small world network is

A

The web has the nice property that there are very few pages that link to many others and a lot of pages that link to very few other pages

40
Q

Schneiderman’s definition of Web Science.

A

the “science of decentralized information systems”

41
Q

define net neutrality

A

Tim Wu, Columbia University media law professor, coining the term in 2003
“Network neutrality is best defined as a network design principle. The idea is
that a maximally useful public information network aspires to treat all
content, sites, and platforms equally.

42
Q

summarize the key arguments of the parties in favour of net neutrality and those who oppose it.

A

Netherlands - Second country with
Network Neutrality
Law (after Chile)
2011-2013

USA - Title II Net
Neutrality rules passed

43
Q

the motivation for, and concepts underlying Linked Open Data

A

Motivation: connect data across silos

Rules of Linked Data:

  1. Use HTTP URI (Uniform Resource Identifiers) as names for things
  2. When someone looks up a URI, provide useful information, using the standards (RDF)
  3. Include links to other URIs. so that they can discover more things.
44
Q

the motivation for, and concepts underlying re-decentralization of the Web and the Solid framework.

A

Re-decentralizing the Web
and Solid - “Solid (derived from “social linked data”) is a
proposed set of conventions and tools for building
decentralized social applications based on Linked
Data principles. Solid is modular and extensible and it
relies as much as possible on existing W3C standards
and protocols.”

Instead of hosting your data at
the service provider you own
your data and choose apps to
manage it

45
Q

the difference between a research question and a hypothesis

A 
A research question is:
• Also called Problem Statement
• Always a question (ends with a "?")
• Sometimes more than one.
• Has practical and/or theoretical relevance.

HYPOTHESIS:
• Describes the assumed relation between at least two variables
• “If X, then Y.”
• “The larger X, the smaller Y.”
• Website-Layout A enables users to find better relevant information than
Layout B.
• Variables can be any attribute or property of humans, objects or systems

46
Q

what dependent and independent variables are

A

Independent
Variable (cause) influences Dependent
Variable (effect)

In HCI often technology is one independent variable (e.g. website layout)

47
Q

what explorative, descriptive and explanatory research is

A

Explorative (what is related?)
• What factors determine if people come back to visit a website a second time?
• Is there a correlations between characteristics of my visitors and the types of
errors that they make?

Descriptive (what happens?)
• What percentage of people find my website through Google?
• What percentage by typing in the URL directly?

Explanatory (why does it happen?)
• Does the addition of a login function mean that more people come back to my
website a second time?
• Did the revision of the link structure of my website make visitors find what they
were looking for quicker?

48
Q

the difference between quantitative and qualitative research

A
  • Qualitative: non numerical, e.g. words, text, pictures or objects
  • Quantitative: analysis of numerical data
  • For quantitative data
  • Use descriptive statistics to describe your results.
  • Use inferential statistics to validate your hypothesis.
  • For qualitative data
  • Use text analysis
  • Affinity diagramming
49
Q

what A/B testing is

A

A/B testing (also known as bucket testing or split-run testing) is a user experience research methodology. A/B tests consist of a randomized experiment with two variants, A and B.

It includes application of statistical hypothesis testing or “two-sample hypothesis testing” as used in the field of statistics.

50
Q

main concepts from the WCAG 2.0

A

accessibility, accessibility guidelines, the principle of perceivability, impact of accessibility on website development.

Web Technology (4 decks)

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