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User interface language: English | Español

Date	November 2020	Marks available	4	Reference code	20N.2.SL.TZ0.7
Level	SL	Paper	2	Time zone	no time zone
Command term	Describe	Question number	7	Adapted from	N/A

Question

Pugh University has a website that allows computer science students to enter their name and customize the web pages.

Consider the section of HTML and CSS code shown below.

File name: index.html

<!DOCTYPE html>
<html>
<body>
<script>
    function setVar(){
    var subject=document.getElementById("kippers").value;
    document.getElementById("subj").innerHTML = subject;
    }
</script>
<h2>My First Page</h2>
<p>Welcome to the <span id="subj"></span> Faculty</p>

<input type="text" id="kippers"/>
<button onclick="setVar();"/>clickme</button>
</body>
</html>

When a student enrolls, they must enter their name on a web page. Before being added to the database, the system should check that the name typed is not blank and that it has not already been added to the database.

Consider the following URL:

https://www.follettibstore.com

The common gateway interface (CGI) offers a standard protocol for web servers.

State the output of the index.html file in the web browser.

[2]

a.i.

Describe the processing that takes place when the user inputs “Pugh” into the text box and then uses the clickme button.

[3]

a.ii.

Explain why these two validation checks occur on different computer systems.

[4]

Explain how website certificates are used to authenticate a user’s browser through secure protocol communications like HTTPS.

[3]

Describe the working of the common gateway interface (CGI).

[4]

Pugh University uses cloud computing services, such as Google Docs or Office 365.

Describe how cloud computing is different to a client–server architecture.

[4]

Markscheme

Award [2 max].
Award [1] for the text within the <p> tags (My First Page large font/Welcome to the Faculty in a smaller font;
Award [1] for the text box and correctly labelled button;

Award [2 max ].
Initially it displays:
My First Page – in large font;
Welcome to the Faculty – in normal font;
A text box + a button labelled “clickme”;
A Then if you type in the text box and then press the button, it displays what is typed between “Welcome to the” and “Faculty” – e.g. type “Science” and it will display; “Welcome to the Science Faculty”;

Note: Students either show the output on the web-browser or describe what would be displayed on the web-browser.

a.i.

Award [3 max].
The button’s onclick method is called, i.e. setVar();
This first sets the variable subject to the value of the HTML element with id kippers, i.e. the text box;
and then sets the inner text of the element with id subj, i.e. the span, to “Pugh”, so that the display is “Welcome to the Pugh Faculty”;

a.ii.

Award [4 max].
Award [1] for identifying correct validation check.
Award [1] for describing the validation check.

Presence check:
It happens in JavaScript in the web page on the client;
because this will save the server handling many transactions/to avoid sending a null value that will need to be handled by the server;

Lookup check
It happens on the server;
because the database is stored on the server rather than on the client’s computer;

Mark as [2] + [2]

Award [3 max].
The website certificate is used to initiate sessions between the user’s browser and the server;
The web server sends the browser a copy of its SSL certificate;
If the browser trusts the certificate, it sends a message to the web server;
The web server sends back a digitally signed acknowledgement to start an SSL encrypted session;

Award [4 max].
The Common Gateway Interface (CGI) is used to provide interactivity to web applications/enable forms to be submitted;
It uses a standard protocol that acts as an intermediary between the CGI program and the web server;
The CGI allows the web server to pass a user’s request to an application program;
And then the forwarded data is received to the user’s browser;

Award [4 max].
Cloud computing is based on sharing computing resources over the internet;
Cloud computing can be offered as a service to individuals and companies (SaaS) which means they do not have to maintain the infrastructure;
Cloud computing and applications are more scalable than client-server architectures;
Client-server architecture does not need to be operating over the internet, but instead can be limited to a local network;
Client-server architectures may require more maintenance of the infrastructure by the organization who are using it;
cloud computing is typically more resilient than client server, because the services offered are more widely distributed, rather than being concentrated on one server or on a small number of alternative servers;

Examiners report

Not all students were familiar with the processing of web scripts. The processing of such scripts is fundamental to the functioning of the web commercially and is an important part of the Web Science course.

a.i.

a.ii.

The question was testing the students' knowledge of client-side and server-side processing. Not many brought this aspect into their answers. As with part (a) more practical experience is recommended.

Poorly answered. Not many understood what these certificates were and even fewer could correctly explain the process involved.

Students were more comfortable with this concept and were aware of its role as an intermediary between application and server.

This was a comparison question which required relating different aspects to both paradigms. It was not answered particularly well.

Syllabus sections

Option C: Web science » C.1 Creating the web

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17N.2.SL.TZ0.8d:

A fragment of a script and a web form are provided below.
In the script some functions are not implemented, and only their specification is provided.

<?php
  //include a database of urls
  include('url_db.php');
  $url = $short = "";

  if ($_SERVER["REQUEST_METHOD"] == "POST")
  { $url = $_POST['url'];
    $short = make_short($url);
    function make_short($u)
    { $x = make_alpha_string($u);
      $y = first4_last4($x);
      $z = limits($x);
      $v = $y. ".".$z;   //string concatenation
      return $v;
  }

  function make_alpha_string($u)
  { // It removes, in this order: substrings corresponding to
    // protocol names, the substring www, and all characters
    // except for letters
  }

  function first4_last4($u)
  { // It returns the string made of the first 4 characters
    // followed by the last 4 characters of $u
  }

  function limits($u)
  { // It returns the string made of the first character and
    // last character of $u
  }

  mysql_query("
    INSERT INTO url_db(orig_url, short_url, url_ip) VALUES
    ( '".$_POST['url']."',
      '".$short."',
      '".$_SERVER['REMOTE_ADDR']."'
    )
  ");
 }
?>

<form method="post" action="">
URL:
<input type="text" name="url" />
<br><br>
<input type="submit" name="Submit" value="Submit" />
</form>

Describe the processing that occurs when the form is filled with the URL https://www.the2nd.org/bin.php?id=70 that the server discovers is associated with the IP address 172.16.254.1.

Hide related questions

Option C: Web science

Question

Markscheme

Examiners report

Syllabus sections

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