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Date	May 2019	Marks available	3	Reference code	19M.2.SL.TZ0.8
Level	SL	Paper	2	Time zone	no time zone
Command term	Identify	Question number	8	Adapted from	N/A

Question

The Large Hadron Collider at CERN in Switzerland produces an average of 15 petabytes (15 million gigabytes) of experimental data every year. This data must be accessed and analysed by scientists around the world.

CERN has established the Worldwide LHC Computing Grid.

With reference to the URL https://home.cern/topics/large-hadron-collider

State the protocol used.

[1]

a.i.

With reference to the URL https://home.cern/topics/large-hadron-collider

Identify the steps taken by the domain name server when the scientist enters a URL such as https://home.cern into their web browser.

[3]

a.ii.

Explain two reasons why CERN would use grid computing to support its research.

[6]

Instead of copyrighting its experimental results, CERN has decided to publish its experimental results using Creative Commons licensing.

Explain two reasons why CERN would publish its experimental results using Creative Commons licensing.

[6]

Markscheme

Award [1 max].
HTTPS / hypertext transport protocol secure;

a.i.

Award [3 max].
The DNS looks up the domain name “home.cern” in its database;
If it doesn’t have this string, it passes the query to another DNS according to defined rules;
This process continues until either an IP address is passed back to the starting DNS or an error message is returned;
The IP address (or error message) is sent back to the client that initiated the call to the DNS;

a.ii.

Award [6 max].
Mark as [3] and [3].

Multiple copies of all or part of the data can be kept at different sites;
This ensures that there is no single point of failure;
and the redundant data helps to ensure against data loss;

Different computers on the grid can use different analysis and data visualization tools;
This allows scientists to run whatever analysis tools best suit their own specialism/area of interest;
Rather than being limited to the tools provided by CERN;

Analysis can be performed using distributed processing time/capacity;
This reduces load and/or reliance on a centralized system;
Allowing a greater number of processes to be run concurrently;

Computers on the grid can be in multiple time zones;
This gives scientists more equitable access to data;
And facilitates round-the-clock monitoring and the availability of expert support;

Resources can be distributed across the world rather than being held in one country;
This may attract funding from governments for their own locally-based research;
As they may see the benefits of international cooperation;

Award [6 max].
Benefits of CC licensing:
CERN want their experimental results to be freely accessible (within specified limits);
Allows for the more rapid dissemination of data/information while preventing people from repackaging them and selling them as a commercial product;
May further the advance of scientific knowledge / be seen as an altruistic gesture;
No need to contact CERN about using the work / allows CERN to focus on their primary function, i.e. scientific research;

Limitations of copyright:
May be impossible to enforce;
Enforcement would require significant costs associated with hiring of lawyers etc.;
It may not be possible to find all cases where work has been used without copyright permissions;
Plagiarism may occur outside of Switzerland where different copyright laws may exist;

Candidates are not required to make comparisons with copyright, however credit should be given where valid limitations of copyright are explained.
Mark as [3] and [3].

Examiners report

The question was answered correctly by most of the candidates.

a.i.

Many candidates reasonably answered this question. However, majority of the candidates failed to score full marks due to lacking specific details of the way the DNS server handles the URL.

a.ii.

Most responses tended to be generic and focused on explaining what grid computing is. Candidates were unable to explain why the grid computing would be useful to support the research. The connection with research was not addressed.

The responses were mostly focused on description of creative common licensing rather than why it was useful for publishing the results.

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.

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Option C: Web science

Question

Markscheme

Examiners report

Syllabus sections

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