<b>MSc Projects</b>

<p>
start of paragraph. <cyan> a <red>cyan</red> word</cyan> normal again something longer.
</p> 


 <p><b>Description:</b>  
  <a>Regular expressions</a> are extremely useful for many text-processing tasks such as finding patterns in texts,
  lexing programs, syntax highlighting and so on. Given that regular expressions were
  introduced in 1950 by <a>Stephen Kleene</a>, you might think 
  regular expressions have since been studied and implemented to death. But you would definitely be mistaken: in fact they are still
  an active research area. For example
  <a>this paper</a> 
  about regular expression matching and partial derivatives was presented this summer at the international 
  PPDP'12 conference. The task in this project is to implement the results from this paper.</p>

  <p>The background for this project is that some regular expressions are 
  <a>evil</a>
  and can stab you in the back; according to
  this <a>blog post</a>.
  For example, if you use in <a>Python</a> or 
  in <a>Ruby</a> (probably also in other mainstream programming languages) the 
  innocently looking regular expression a?{28}a{28} and match it, say, against the string 
  <red>aaaaaaaaaaaaaaaaaaaaaaaaaaaa</red> (that is 28 as), you will soon notice that your CPU usage goes to 100%. In fact,
  Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself:
  <a>re.py</a> (Python version) and 
  <a>re.rb</a> 
  (Ruby version). You can imagine an attacker
  mounting a nice <a>DoS attack</a> against 
  your program if it contains such an evil regular expression. Actually 
  <a>Scala</a> (and also Java) are almost immune from such
  attacks as they can deal with strings of up to 4,300 as in less than a second. But if you scale
  the regular expression and string further to, say, 4,600 as, then you get a 
  StackOverflowError 
  potentially crashing your program.
  </p>