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User interface language: English | Español

Date	November 2018	Marks available	4	Reference code	18N.2.SL.TZ0.7
Level	SL	Paper	2	Time zone	no time zone
Command term	Explain	Question number	7	Adapted from	N/A

Question

The online edition of a newspaper includes a collection of audio podcasts. These podcasts are interviews with artists and scientists and last for up to 10 minutes. They may have been provided by other broadcasters and agencies.

At any time, no more than eight podcasts are available on the online edition of the newspaper.

The podcasts can either be downloaded or streamed.

The podcast can be stored online using either lossy or lossless compression.

A person is streaming one of these podcasts at home. However, he is experiencing buffering problems, where the podcast keeps stopping and starting.

Identify two actions relating to the source of these podcasts that should be taken by the newspaper before publishing them.

[2]

Outline one technical reason for restricting the number of podcasts to eight.

[2]

State one format for an audio file.

[1]

Compare these two approaches for a person who downloads or streams these podcasts.

[5]

Outline one reason for this problem.

[2]

These podcasts are normally displayed on the website in the chronological order in which they were added, with the most recent on top. However, users who regularly access the site for science podcasts, may see them presented in a different order, with all the scientific ones on top.

With reference to the technology involved, explain how this is made possible.

[4]

Markscheme

Award up to [2 max].
Provide a reference to the source/provider;
Obtain permission from the interviewee;

Award up to [2 max].
To better control access to their servers;
Because it could be cause of bottleneck on the server / to reduce/minimize risks of DDoS;

To better manage the UI;
So that the offer of podcasts is well visible also from small devices;

To have a smaller system that is easier to maintain;
That can be maintained more effectively also remotely by one person;

Award up to [1 max].
(accept for general sound format:) MP3, FLAC, WAV, WMA;

Award up to [5 max].
Award up to [4 max] for comparing lossless and lossy.
Award [1] for a conclusion with reference to the scenario.

In terms of audio quality for spoken language there is not much difference in using lossy or lossless compression/ lossless compression does not really bring benefit to the spoken audio;

A minor benefit could be in using lossy compression in relation to transmission while downloading (and also in streaming);

And it is relevant, in general, in a situation with low bandwidth;

However, these files are small in size anyway, because their duration is limited to 10 minutes;

And this suggests that for the specific nature and size of the files (spoken and 10 minutes duration) lossy might be slightly preferable for some users for downloading without compromising on quality of audio.

Award up to [2 max].
Award [1] for identifying a reason why buffering may occur and [1] expansion/example up to [2 max].

Too many people are using their own Internet access point at home simultaneously;
Possibly on different devices, including tablets, smartphones on WiFi;

There is low bandwidth because it is peak time;
Possibly too many people are downloading simultaneously;

Old router/modem/computer / outdated software may slow performance;
Computer that is not protected by antivirus may have performance affected by malware;
Performance;

There are too many applications running simultaneously on the computer;
So, memory is insufficient and one should close some applications;

Award up to [4 max].
Award up to [2 max] for the use of dynamic scripting.
Award up to [2 max] for the means of tracking a person’s preferences.

Dynamic web pages / scripting
Podcasts are associated to XML objects;
So, that the list of podcasts can be processed by scripts that can re-arrange the order of the XML objects;
To present them in a way that takes into account the previous uses from the user;
By monitoring their preferences, over time;

Tracking a person’s preferences
For example, counting the clicks and themes to extract regularities / support data analytics;
That can be identified for example by the IP of their device when this is not anonymised;
And also stored in the history of the browser/by use of cookies;

Examiners report

[N/A]

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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