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<TITLE>2012/13 MSc Projects</TITLE>
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<H2>2012/13 MSc Projects</H2>
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<H4>Supervisor: Christian Urban</H4>
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<H4>Email: christian dot urban at kcl dot ac dot uk, Office: Strand Building S1.27</H4>
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<H4>If you are interested in a project, please send me an email and we can discuss details. Please include
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a short description about your programming skills and Computer Science background in your first email.
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I will also need your King's username in order to book the project for you. Thanks.</H4>
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<H4>Note that besides being a lecturer in the theoretical part of Computer Science, I am also a passionate
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<A HREF="http://en.wikipedia.org/wiki/Hacker_(programmer_subculture)">hacker</A> …
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defined as “a person who enjoys exploring the details of programmable systems and
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stretching their capabilities, as opposed to most users, who prefer to learn only the minimum
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necessary.” I am always happy to supervise like-minded students.</H4>
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<ul class="striped">
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<li> <H4>[CU1] Regular Expression Matching and Partial Derivatives</H4>
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<p>
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<B>Description:</b>
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<A HREF="http://en.wikipedia.org/wiki/Regular_expression">Regular expressions</A>
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are extremely useful for many text-processing tasks such as finding patterns in texts,
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lexing programs, syntax highlighting and so on. Given that regular expressions were
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introduced in 1950 by <A HREF="http://en.wikipedia.org/wiki/Stephen_Cole_Kleene">Stephen Kleene</A>, you might think
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regular expressions have since been studied and implemented to death. But you would definitely be mistaken: in fact they are still
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an active research area. For example
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<A HREF="http://www.home.hs-karlsruhe.de/~suma0002/publications/ppdp12-part-deriv-sub-match.pdf">this paper</A>
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about regular expression matching and partial derivatives was presented this summer at the international
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PPDP'12 conference. The task in this project is to implement the results from this paper.</p>
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<p>The background for this project is that some regular expressions are
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“<A HREF="http://en.wikipedia.org/wiki/ReDoS#Examples">evil</A>”
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and can “stab you in the back” according to
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this <A HREF="http://tech.blog.cueup.com/regular-expressions-will-stab-you-in-the-back">blog post</A>.
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For example, if you use in <A HREF="http://www.python.org">Python</A> or
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in <A HREF="http://www.ruby-lang.org/en/">Ruby</A> (probably also in other mainstream programming languages) the
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innocently looking regular expression <code>a?{28}a{28}</code> and match it, say, against the string
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<code>aaaaaaaaaaaaaaaaaaaaaaaaaaaa</code> (that is 28 <code>a</code>s), you will soon notice that your CPU usage goes to 100%. In fact,
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Python and Ruby need approximately 30 seconds of hard work for matching this string. You can try it for yourself:
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/cgi-bin/repos.cgi/afl-material/raw-file/tip/re.py">re.py</A> (Python version) and
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/cgi-bin/repos.cgi/afl-material/raw-file/tip/re-internal.rb">re.rb</A>
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(Ruby version). You can imagine an attacker
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mounting a nice <A HREF="http://en.wikipedia.org/wiki/Denial-of-service_attack">DoS attack</A> against
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your program if it contains such an “evil” regular expression. Actually
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<A HREF="http://www.scala-lang.org/">Scala</A> (and also Java) are almost immune from such
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attacks as they can deal with strings of up to 4,300 <code>a</code>s in less than a second. But if you scale
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the regular expression and string further to, say, 4,600 <code>a</code>s, then you get a <code>StackOverflowError</code>
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potentially crashing your program.
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</p>
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<p>
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On a rainy afternoon, I implemented
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/cgi-bin/repos.cgi/afl-material/raw-file/tip/re3.scala">this</A>
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regular expression matcher in Scala. It is not as fast as the official one in Scala, but
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it can match up to 11,000 <code>a</code>s in less than 5 seconds without raising any exception
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(remember Python and Ruby both need nearly 30 seconds to process 28(!) <code>a</code>s, and Scala's
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official matcher maxes out at 4,600 <code>a</code>s). My matcher is approximately
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85 lines of code and based on the concept of
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<A HREF="http://lambda-the-ultimate.org/node/2293">derivatives of regular expressions</A>.
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These derivatives were introduced in 1964 by <A HREF="http://en.wikipedia.org/wiki/Janusz_Brzozowski_(computer_scientist)">
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Janusz Brzozowski</A>, but according to this
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<A HREF="http://www.cl.cam.ac.uk/~so294/documents/jfp09.pdf">paper</A> had been lost in the “sands of time”.
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The advantage of derivatives is that they side-step completely the usual
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<A HREF="http://hackingoff.com/compilers/regular-expression-to-nfa-dfa">translations</A> of regular expressions
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into NFAs or DFAs, which can introduce the exponential behaviour exhibited by the regular
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expression matchers in Python and Ruby.
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</p>
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<p>
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Now the guys from the
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<A HREF="http://www.home.hs-karlsruhe.de/~suma0002/publications/ppdp12-part-deriv-sub-match.pdf">PPDP'12-paper</A> mentioned
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above claim they are even faster than me and can deal with even more features of regular expressions
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(for example subexpression matching, which my rainy-afternoon matcher cannot). I am sure they thought
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about the problem much longer than a single afternoon. The task
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in this project is to find out how good they actually are by implementing the results from their paper.
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Their approach is based on the concept of partial derivatives introduced in 1994 by
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<A HREF="http://reference.kfupm.edu.sa/content/p/a/partial_derivatives_of_regular_expressio_1319383.pdf">Valentin Antimirov</A>.
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I used them once myself in a <A HREF="http://www.inf.kcl.ac.uk/staff/urbanc/Publications/rexp.pdf">paper</A>
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in order to prove the <A HREF="http://en.wikipedia.org/wiki/Myhill–Nerode_theorem">Myhill-Nerode theorem</A>.
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So I know they are worth their money. Still, it would be interesting to actually compare their results
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with my simple rainy-afternoon matcher and potentially “blow away” the regular expression matchers
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in Python and Ruby (and possibly in Scala too).
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</p>
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<p>
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<B>Literature:</B>
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The place to start with this project is obviously this
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<A HREF="http://www.home.hs-karlsruhe.de/~suma0002/publications/ppdp12-part-deriv-sub-match.pdf">paper</A>.
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Traditional methods for regular expression matching are explained
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in the Wikipedia articles
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<A HREF="http://en.wikipedia.org/wiki/DFA_minimization">here</A> and
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<A HREF="http://en.wikipedia.org/wiki/Powerset_construction">here</A>.
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The authoritative <A HREF="http://infolab.stanford.edu/~ullman/ialc.html">book</A>
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on automata and regular expressions is by John Hopcroft and Jeffrey Ullmann (available in the library).
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There is also an online course about this topic by Ullman at
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<A HREF="https://www.coursera.org/course/automata">Coursera</A>, though IMHO not
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done with love.
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Finally, there are millions of other pointers about regular expression
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matching on the Net. Test cases for “<A HREF="http://en.wikipedia.org/wiki/ReDoS#Examples">evil</A>”
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regular expressions can be obtained from <A HREF="http://en.wikipedia.org/wiki/ReDoS#Examples">here</A>.
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</p>
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<p>
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<B>Skills:</B>
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This is a project for a student with an interest in theory and some
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reasonable programming skills. The project can be easily implemented
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in languages like
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<A HREF="http://www.scala-lang.org/">Scala</A>,
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<A HREF="http://en.wikipedia.org/wiki/Standard_ML">ML</A>,
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<A HREF="http://haskell.org/haskellwiki/Haskell">Haskell</A>,
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<A HREF="http://www.python.org">Python</A>, etc.
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</p>
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<li> <H4>[CU2] Automata Theory in Your Web-Browser</H4>
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<p>
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This project is about web-programming (but not in Java):
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There are a number of classic algorithms in automata theory (such as the
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<A HREF="http://hackingoff.com/compilers/regular-expression-to-nfa-dfa">transformation</A> of regular
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expressions into NFAs and DFAs,
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<A HREF="http://en.wikipedia.org/wiki/DFA_minimization">automata minimisation</A>,
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<A HREF="http://en.wikipedia.org/wiki/Powerset_construction">subset construction</A>).
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All these algorithms involve a fair
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amount of calculations, which cannot be easily done by hand. There are a few web applications, typically
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written in <A HREF="http://en.wikipedia.org/wiki/JavaScript">Javascript</A>, that animate these
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calculations, for example <A HREF="http://hackingoff.com/compilers/regular-expression-to-nfa-dfa">this one<A/>.
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But they all have their deficiencies and can be improved with more modern technology.
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An instance is the impressive animation of Phython code found
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<A HREF="http://www.pythontutor.com">here</A>.
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</p>
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<p>
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There now many useful libraries for JavaScript, for example, this
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<A HREF="http://getspringy.com">one</A> for graphs or this
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<A HREF="http://demos.bonsaijs.org/demos/star/index.html">one</A> for graphics.
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There are also
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a number of new programming languages targeting JavaScript, for example
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<A HREF="http://www.typescriptlang.org">TypeScript</A>,
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<A HREF="http://coffeescript.org">CoffeeScript</A>,
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<A HREF="http://www.dartlang.org">Dart</A>,
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<A HREF="http://scriptsharp.com">Script#</A>,
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<A HREF="http://clojure.org">Clojure</A>
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and so on.
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The task in this project is to use a web-programming
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language and suitable library to animate algorithms from automata theory (and also parsing, if wanted).
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This project is for someone who
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want to get to know these new languages.
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</p>
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<B>Literature:</B>
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The same general literature as in [CU1].
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</p>
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<p>
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<B>Skills:</B>
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This is a project for a student with very good programming
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and <A HREF="http://en.wikipedia.org/wiki/Hacker_(programmer_subculture)">hacking</A> skills.
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Some knowledge in JavaScript, HTML and CSS cannot hurt. The algorithms from automata
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theory are fairly standard material.
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</p>
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<!--
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<li> <H4>[CU2] Equivalence Checking of Regular Expressions</H4>
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<p>
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<B>Description:</b>
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Solving the problem of deciding the equivalence of regular expressions can be used
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to decide a number of problems in automated reasoning. Recently,
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<A HREF="http://www.cs.unibo.it/~asperti/">Andreas Asperti</A>
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proposed a simple method for deciding regular expression equivalence described
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<A HREF="http://www.cs.unibo.it/~asperti/PAPERS/compact.pdf">here</A>.
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The task is to implement this method and test it on examples.
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It would be also interesting to see whether Asperti's method applies to
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extended regular expressions, described
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<A HREF="http://ww2.cs.mu.oz.au/~sulzmann/manuscript/reg-exp-partial-derivatives.pdf">here</A>.
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</p>
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<p>
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<B>Literature:</B>
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The central literature is obviously the papers
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<A HREF="http://www.cs.unibo.it/~asperti/PAPERS/compact.pdf">here</A> and
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<A HREF="http://ww2.cs.mu.oz.au/~sulzmann/manuscript/reg-exp-partial-derivatives.pdf">here</A>.
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Asperti has also some slides <A HREF="http://www.cs.unibo.it/~asperti/SLIDES/regular.pdf">here</a>.
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More references about regular expressions can be found
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<A HREF="http://en.wikipedia.org/wiki/Regular_expression">here</A>. Like in
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[CU1], I will give a lot of the background pf this project in
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my Automata and Formal Languages course (6CCS3AFL).
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</p>
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<p>
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<B>Skills:</B>
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This is a project for a student with a passion for theory and some
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reasonable programming skills. The project can be easily implemented
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in languages like Scala
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<A HREF="http://www.scala-lang.org/">Scala</A>,
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<A HREF="http://en.wikipedia.org/wiki/Standard_ML">ML</A>,
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<A HREF="http://haskell.org/haskellwiki/Haskell">Haskell</A>,
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<A HREF="http://www.python.org">Python</A>, etc.
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Being able to read <A HREF="http://haskell.org/haskellwiki/Haskell">Haskell</A>
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code is beneficial for the part involving extended regular expressions.
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</p>
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-->
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<li> <H4>[CU3] Machine Code Generation for a Simple Compiler</H4>
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<p>
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<b>Description:</b>
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Compilers translate high-level programs that humans can read into
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efficient machine code that can be run on a CPU or virtual machine.
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I recently implemented a very simple compiler for a very simple functional
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programming language following this
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<A HREF="http://www.cs.princeton.edu/~dpw/papers/tal-toplas.pdf">paper</A>
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(also described <A HREF="http://www.cs.princeton.edu/~dpw/papers/tal-tr.pdf">here</A>).
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My code, written in <A HREF="http://www.scala-lang.org/">Scala</A>, of this compiler is
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/compiler.scala">here</A>.
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The compiler can deal with simple programs involving natural numbers, such
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as Fibonacci
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or factorial (but it can be easily extended - that is not the point).
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</p>
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<p>
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While the hard work has been done (understanding the two papers above),
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my compiler only produces some idealised machine code. For example I
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assume there are infinitely many registers. The goal of this
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project is to generate machine code that is more realistic and can
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run on a CPU, like x86, or run on a virtual machine, say the JVM.
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This gives probably a speedup of thousand times in comparison to
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my naive machine code and virtual machine. The project
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requires to dig into the literature about real CPUs and generating
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real machine code.
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</p>
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<p>
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<B>Literature:</B>
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There is a lot of literature about compilers
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(for example <A HREF="http://www.cs.princeton.edu/~appel/papers/cwc.html">this book</A> -
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I can lend you my copy for the duration of the project). A very good overview article
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about implementing compilers by
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<A HREF="http://tratt.net/laurie/">Laurie Tratt</A> is
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<A HREF="http://tratt.net/laurie/tech_articles/articles/how_difficult_is_it_to_write_a_compiler">here</A>.
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An introduction into x86 machine code is <A HREF="http://ianseyler.github.com/easy_x86-64/">here</A>.
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Intel's official manual for the x86 instruction is
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<A HREF="http://download.intel.com/design/intarch/manuals/24319101.pdf">here</A>.
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A simple assembler for the JVM is described <A HREF="http://jasmin.sourceforge.net">here</A>.
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An interesting twist of this project is to not generate code for a CPU, but
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for the intermediate language of the <A HREF="http://llvm.org">LLVM</A> compiler
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(also described <A HREF="https://wiki.aalto.fi/display/t1065450/LLVM+IR">here</A> and
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<A HREF="http://llvm.org/docs/LangRef.html">here</A>). If you want to see
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what machine code looks like you can compile your C-program using gcc -S.
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</p>
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<p>
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<B>Skills:</B>
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This is a project for a student with a deep interest in programming languages and
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compilers. Since my compiler is implemented in <A HREF="http://www.scala-lang.org/">Scala</A>,
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it would make sense to continue this project in this language. I can be
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of help with questions and books about <A HREF="http://www.scala-lang.org/">Scala</A>.
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But if Scala is a problem, my code can also be translated quickly into any other
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language.
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</p>
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<li> <H4>[CU4] Implementation of Register Spilling Algorithms</H4>
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<p>
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<b>Description:</b>
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This project is similar to [CU3]. The emphasis here, however, is on the
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implementation and comparison of register spilling algorithms, also often called register allocation
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algorithms. They are part of any respectable compiler. As said
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165
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in [CU3] my simple compiler lacks them and assumes an infinite amount of registers instead.
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Real CPUs however only provide a fixed amount of registers (for example
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x86-64 has 16 general purpose registers). Whenever a program needs
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to hold more values than registers, the values need to be “spilled”
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into the main memory. Register spilling algorithms try to minimise
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this spilling, since fetching values from main memory is a costly
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operation.
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</p>
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<p>
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The classic algorithm for register spilling uses a
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<A HREF="http://en.wikipedia.org/wiki/Register_allocation">graph-colouring method</A>.
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However, for some time the <A HREF="http://llvm.org">LLVM</A> compiler
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used a supposedly more efficient method, called the linear scan allocation method
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(described
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<A HREF="http://www.cs.ucla.edu/~palsberg/course/cs132/linearscan.pdf">here</A>).
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However, it was later decided to abandon this method in favour of
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a <A HREF="http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html">
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greedy register allocation</A> method. It would be nice if this project can find out
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what the issues are with these methods and implement at least one of them for the
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simple compiler referenced in [CU3].
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</p>
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<p>
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<B>Literature:</B>
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The graph colouring method is described in Andrew Appel's
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<A HREF="http://www.cs.princeton.edu/~appel/modern/java/">book</A> on compilers
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(I can give you my copy of this book, if it is not available in the library).
|
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|
328 |
There is also a survey
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<A HREF="http://compilers.cs.ucla.edu/fernando/publications/drafts/survey.pdf">article</A>
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about register allocation algorithms with further pointers.
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</p>
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332 |
|
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333 |
<p>
|
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|
334 |
<B>Skills:</B>
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|
335 |
Same skills as [CU3].
|
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336 |
</p>
|
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337 |
|
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|
338 |
<li> <H4>[CU5] A Student Polling System</H4>
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339 |
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|
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<p>
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341 |
<B>Description:</B>
|
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342 |
One of the more annoying aspects of giving a lecture is to ask a question
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343 |
to the students and no matter how easy the questions is to not
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receive an answer. Recently, the online course system
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345 |
<A HREF="http://www.udacity.com">Udacity</A> made an art out of
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346 |
asking questions during lectures (see for example the
|
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347 |
<A HREF="http://www.udacity.com/overview/Course/cs253/CourseRev/apr2012">Web Application Engineering</A>
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course CS253).
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349 |
The lecturer there gives multiple-choice questions as part of the lecture and the students need to
|
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350 |
click on the appropriate answer. This works very well in the online world.
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351 |
For “real-world” lectures, the department has some
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352 |
<A HREF="http://en.wikipedia.org/wiki/Audience_response">clickers</A>
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(these are little devices part of an audience response systems). However,
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they are a logistic nightmare for the lecturer: they need to be distributed
|
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355 |
during the lecture and collected at the end. Nowadays, where students
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356 |
come with their own laptop or smartphone to lectures, this can
|
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|
357 |
be improved.
|
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|
358 |
</p>
|
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|
359 |
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|
360 |
<p>
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361 |
The task of this project is to implement an online student
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|
362 |
polling system. The lecturer should be able to prepare
|
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questions beforehand (encoded as some web-form) and be able to
|
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|
364 |
show them during the lecture. The students
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|
365 |
can give their answers by clicking on the corresponding webpage.
|
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366 |
The lecturer can then collect the responses online and evaluate them
|
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367 |
immediately. Such a system is sometimes called
|
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368 |
<A HREF="http://en.wikipedia.org/wiki/Audience_response#Smartphone_.2F_HTTP_voting">HTML voting</A>.
|
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369 |
There are a number of commercial
|
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|
370 |
solutions for this problem, but they are not easy to use (in addition
|
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|
371 |
to being ridiculously expensive). A good student can easily improve upon
|
|
|
372 |
what they provide.
|
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|
373 |
</p>
|
|
|
374 |
|
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|
375 |
<p>
|
|
|
376 |
The problem of student polling is not as hard as
|
|
|
377 |
<A HREF="http://en.wikipedia.org/wiki/Electronic_voting">electronic voting</A>,
|
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|
378 |
which essentially is still an unsolved problem in Computer Science. The
|
|
|
379 |
students only need to be prevented from answering question more than once thus skewing
|
|
|
380 |
any statistics. Unlike electronic voting, no audit trail needs to be kept
|
|
|
381 |
for student polling. Restricting the number of answers can probably be solved
|
|
163
|
382 |
by setting appropriate cookies on the students'
|
|
154
|
383 |
computers or smart phones.
|
|
|
384 |
</p>
|
|
|
385 |
|
|
|
386 |
<p>
|
|
163
|
387 |
However, there is one restriction that makes this project harder than it seems
|
|
165
|
388 |
at first sight: The department does not allow large server applications and databases
|
|
|
389 |
to be run on calcium, which is the central server in the department. So the problem
|
|
|
390 |
should be solved with as few resources as possible
|
|
|
391 |
on the “back-end” collecting the votes.
|
|
163
|
392 |
</p>
|
|
|
393 |
|
|
|
394 |
<p>
|
|
154
|
395 |
<B>Literature:</B>
|
|
|
396 |
The project requires fluency in a web-programming language (for example
|
|
164
|
397 |
<A HREF="http://en.wikipedia.org/wiki/JavaScript">JavaScript</A>,
|
|
154
|
398 |
<A HREF="http://en.wikipedia.org/wiki/PHP">PHP</A>,
|
|
|
399 |
Java, <A HREF="http://www.python.org">Python</A>,
|
|
|
400 |
<A HREF="http://en.wikipedia.org/wiki/Go_(programming_language)">Go</A>,
|
|
|
401 |
<A HREF="http://www.scala-lang.org/">Scala</A>,
|
|
163
|
402 |
<A HREF="http://en.wikipedia.org/wiki/Ruby_(programming_language)">Ruby</A>).
|
|
154
|
403 |
For web-programming the
|
|
|
404 |
<A HREF="http://www.udacity.com/overview/Course/cs253/CourseRev/apr2012">Web Application Engineering</A>
|
|
|
405 |
course at <A HREF="http://www.udacity.com">Udacity</A> is a good starting point
|
|
|
406 |
to be aware of the issues involved. This course uses <A HREF="http://www.python.org">Python</A>.
|
|
|
407 |
To evaluate the answers from the student, Google's
|
|
|
408 |
<A HREF="https://developers.google.com/chart/image/docs/making_charts">Chart Tools</A>
|
|
164
|
409 |
might be useful, which are also described in this
|
|
154
|
410 |
<A HREF="http://www.youtube.com/watch?v=NZtgT4jgnE8">youtube</A> video.
|
|
|
411 |
</p>
|
|
|
412 |
|
|
|
413 |
<p>
|
|
|
414 |
<B>Skills:</B>
|
|
163
|
415 |
This project needs very good web-programming skills. A
|
|
154
|
416 |
<A HREF="http://en.wikipedia.org/wiki/Hacker_(programmer_subculture)">hacker mentality</A>
|
|
|
417 |
(see above) is probably very beneficial: web-programming is an area that only emerged recently and
|
|
|
418 |
many tools still lack maturity. You probably have to experiment a lot with several different
|
|
|
419 |
languages and tools.
|
|
|
420 |
</p>
|
|
|
421 |
|
|
|
422 |
<li> <H4>[CU6] Implementation of a Distributed Clock-Synchronisation Algorithm developed at NASA</H4>
|
|
|
423 |
|
|
|
424 |
<p>
|
|
|
425 |
<B>Description:</B>
|
|
|
426 |
There are many algorithms for synchronising clocks. This
|
|
|
427 |
<A HREF="http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120000054_2011025573.pdf">paper</A>
|
|
164
|
428 |
describes a new algorithm developed by NASA for clocks that communicate by exchanging
|
|
154
|
429 |
messages and thereby reach a state in which (within some bound) all clocks are synchronised.
|
|
|
430 |
A slightly longer and more detailed paper about the algorithm is
|
|
|
431 |
<A HREF="http://hdl.handle.net/2060/20110020812">here</A>.
|
|
164
|
432 |
The point of this project is to implement this algorithm and simulate a networks of clocks.
|
|
154
|
433 |
</p>
|
|
|
434 |
|
|
|
435 |
<p>
|
|
|
436 |
<B>Literature:</B>
|
|
164
|
437 |
There is a wide range of literature on clock synchronisation algorithms.
|
|
154
|
438 |
Some pointers are given in this
|
|
|
439 |
<A HREF="http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120000054_2011025573.pdf">paper</A>,
|
|
|
440 |
which describes the algorithm to be implemented in this project. Pointers
|
|
|
441 |
are given also <A HREF="http://en.wikipedia.org/wiki/Clock_synchronization">here</A>.
|
|
|
442 |
</p>
|
|
|
443 |
|
|
|
444 |
<p>
|
|
|
445 |
<B>Skills:</B>
|
|
|
446 |
In order to implement a simulation of a network of clocks, you need to tackle
|
|
|
447 |
concurrency. You can do this for example in the programming language
|
|
|
448 |
<A HREF="http://www.scala-lang.org/">Scala</A> with the help of the
|
|
|
449 |
<A HREF="http://akka.io">Akka</a> library. This library enables you to send messages
|
|
|
450 |
between different <I>actors</I>. <A HREF="http://www.scala-lang.org/node/242">Here</A>
|
|
|
451 |
are some examples that explain how to implement exchanging messages between actors.
|
|
|
452 |
</p>
|
|
|
453 |
|
|
|
454 |
</ul>
|
|
|
455 |
</TD>
|
|
|
456 |
</TR>
|
|
|
457 |
</TABLE>
|
|
|
458 |
|
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|
459 |
<P>
|
|
|
460 |
<!-- Created: Tue Mar 4 00:23:25 GMT 1997 -->
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|
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<!-- hhmts start -->
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|
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Last modified: Wed Sep 12 16:30:03 GMT 2012
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<!-- hhmts end -->
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<a href="http://validator.w3.org/check/referer">[Validate this page.]</a>
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