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Date	November 2017	Marks available	3	Reference code	17N.2.SL.TZ0.7
Level	SL	Paper	2	Time zone	no time zone
Command term	Explain	Question number	7	Adapted from	N/A

Question

BuildYourWebSite is an online company that provides a number of common templates for building your own website. Each template includes one HTML file, one CSS file, a folder of web images, and a folder of special sound effects.

Each template can be downloaded as a single compressed file, using a web browser.

Identify two characteristics of HTML.

[2]

Discuss the benefits and disadvantages of the template including a CSS file in addition to the HTML page.

[6]

Explain why TCP/IP is a reliable protocol in relation to downloading operations.

[3]

Evaluate lossy compression and lossless compression when used to download files.

[4]

Markscheme

Award up to [2 max].
Mark-up language;
Can contain scripting commands/code;
Can imbed objects;
Uses tags to structure page;
Provides constructs to build hyperlinks;
Can be integrated with CSS and JavaScript;
Note: Accept other reasonable characteristics.

Award marks as follows up to [6 max].
Award [1] for identifying an advantage, [1] for identifying a disadvantage, and a further [4 max] for expanding on these advantages/disadvantages.

Advantages
It saves time (in web development);
Because modification of style needs to only be made to the CSS;
It saves space;
Because the code (of the style) is not repeated in each HTML file;
Quicker load of many pages / Quicker download of many pages from the same site;
HTML files are smaller;
It gives a uniform appearance to the entire website;
Which makes it more attractive/appealing/easy to navigate;
It can be integrated with outside sources (e.g. RSS feeds);
Which makes the website more interactive/dynamic for the user;
Quicker to make changes to layout/formatting/page positioning;
Therefore, it helps separating the jobs/tasks of illustrators (designer) from those that produce content;
Increases accessibility of authoring to non-experts;
Supported by most browsers;
Increasing the number of users;

Disadvantages:
Downloading pages from different sites can be slow (general browsing);
Because each page may have its own CSS;
(However, downloading many pages from the same site is instead faster;)
CSS syntax is different from HTML and can be slightly ambiguous;
Not a user-friendly language (but available as IDE) that the developer needs to learn;
(e.g. the same cascade style name may have slightly different effects when used by different browsers;)
An HTML page saved without CSS, and seen offline, will not display nicely;
Because it would require access to external files, including CSS (including images, video, sound);
Anybody with read/write permission to the CSS can easily override just the CSS;
Showing unwanted information to an entire web-site (risk of hacking in just one point/internal threat with high risk);
Some browsers do not support exactly the same CSS (some styles/fonts for example);
The view can be slightly different using different browsers/risk of slight incompatibility;
(For large, corporate sites) Integration of HTML + CSS with other content management systems (CMS) may be tricky;
Because CMS also use their own CSS, and there can be collisions, and it requires technical competence;

Award up to [3 max].
(When a request of download is received at the Application level (e.g. HTTP with a browser), appropriate data packets are generated and sent to the transport layer/TCP;)

TCP uses the header of the data packets to order them and to check their contents;
And sends an acknowledgement signal to the transmitter upon correct reception, before preparing a new data packet with a further header for the IP/Internet level;
If the transmitter does not receive the acknowledgement from the TCP, the transmitter re-sends the packet;
Therefore, all correct packets will be available to the TCP at some point to be made available to the IP and specifically to the IP destination/receiver (in the header);
IP ensures that the package reaches the correct address;

Award marks as follows up to [4 max].
Award [1 max] each for outlining the two techniques (lossy and lossless).
Award [up to 2 max] for relating both to actual applications ([1] if related to file types instead).

Images and audio can be compressed using lossy techniques;
This will create a smaller file/faster transmission time;
But the data loss will not seriously affect quality;

However, CSS and HTML files might lose possible scripting;
As you need to recover the original data;
Lossless compression is more suitable;

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

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Syllabus sections

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