# HG changeset patch # User Chengsong # Date 1557349799 -3600 # Node ID c51178fa85fecb634efa9010d08f5eae3d9f1204 # Parent cd0ceaf89c1d24ea3ff6eb23ac43df3dd0b525d9 new version of slides diff -r cd0ceaf89c1d -r c51178fa85fe Spiral.scala --- a/Spiral.scala Sun May 05 22:02:29 2019 +0100 +++ b/Spiral.scala Wed May 08 22:09:59 2019 +0100 @@ -445,19 +445,19 @@ val r = ("ab"| SEQ(ONE, "ab"))//internalise(random_struct_gen(4))//ASTAR(List(),AALTS(List(),List(ASTAR(List(Z),ACHAR(List(),'a')), ASEQ(List(S),ACHAR(List(),'a'),ACHAR(List(),'b')))))//internalise(balanced_struct_gen(3))//SEQ(ALTS(List(STAR("a"),ALTS(List("a","c")))),SEQ(ALTS(List("c","a")),ALTS(List("c","b")))) //random_struct_gen(7) for(j <- 0 to s.length - 1){ val ss = s.slice(0, j+ 1) - val nangao = ders_simp(r, ss.toList) - val easy = bsimp(bders(ss.toList, r)) + val nangao = ders_simp(internalise(r), ss.toList) + val easy = bsimp(bders(ss.toList, internalise(r))) if(!(nangao == easy || pushbits(nangao) == (easy))){ println(j) println("not equal") println("string") println(ss) println("original regex") - println(annotated_tree(r)) + println(regx_tree(r)) println("regex after ders simp") println(annotated_tree(nangao)) println("regex after ders") - println(annotated_tree(bders(ss.toList, r)))//flats' fuse when opening up AALTS causes the difference + println(annotated_tree(bders(ss.toList, internalise(r))))//flats' fuse when opening up AALTS causes the difference println("regex after ders and then a single simp") println(annotated_tree(easy)) } @@ -551,16 +551,24 @@ println(bs3) } def essence_posix(){ - val s = "abab"//rd_string_gen(alphabet_size, 3)//"abaa"//rd_string_gen(alphabet_size, 3) - val r = STAR("ab"| SEQ(ONE, "ab"))//internalise(random_struct_gen(4))//ASTAR(List(),AALTS(List(),List(ASTAR(List(Z),ACHAR(List(),'a')), ASEQ(List(S),ACHAR(List(),'a'),ACHAR(List(),'b')))))//internalise(balanced_struct_gen(3))//SEQ(ALTS(List(STAR("a"),ALTS(List("a","c")))),SEQ(ALTS(List("c","a")),ALTS(List("c","b")))) //random_struct_gen(7) - ders(s.toList, r) + //val s = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"//rd_string_gen(alphabet_size, 3)//"abaa"//rd_string_gen(alphabet_size, 3) + val s0 = "a" + val r = SEQ(STAR(ALT("a", "aa")), "b")//internalise(random_struct_gen(4))//ASTAR(List(),AALTS(List(),List(ASTAR(List(Z),ACHAR(List(),'a')), ASEQ(List(S),ACHAR(List(),'a'),ACHAR(List(),'b')))))//internalise(balanced_struct_gen(3))//SEQ(ALTS(List(STAR("a"),ALTS(List("a","c")))),SEQ(ALTS(List("c","a")),ALTS(List("c","b")))) //random_struct_gen(7) + for(i <- 1 to 40){ + val s = s0*i + //printf("%d %d\n",i, size(ders(s.toList, r))) + printf("%d %d\n",i, asize(ders_simp( internalise(r), s.toList))) + //println(asize(ders_simp( internalise(r), s.toList))) + } } + def main(args: Array[String]) { //check_all() //radical_correctness() //correctness_proof_convenient_path() //retrieve_experience() - christian_def() + //christian_def() + essence_posix() } } diff -r cd0ceaf89c1d -r c51178fa85fe lex_blex_Frankensteined.scala --- a/lex_blex_Frankensteined.scala Sun May 05 22:02:29 2019 +0100 +++ b/lex_blex_Frankensteined.scala Wed May 08 22:09:59 2019 +0100 @@ -415,7 +415,7 @@ def flats_vsimp(rs: List[ARexp], position: Int): Int = (rs, position) match { case (_, 0) => 0 case (Nil, _) => 0 - case (ZERO :: rs1, _) => flats_vsimp(rs1, position - 1) - 1 + case (AZERO :: rs1, _) => flats_vsimp(rs1, position - 1) - 1 case (AALTS(bs, rs1) :: rs2, _) => rs1.length - 1 + flats_vsimp(rs2, position - 1) case (r1 :: rs2, _) => flats_vsimp(rs2, position - 1) } @@ -448,29 +448,29 @@ //case ASTAR(bs, r) => ASTAR(bs, bsimp(r)) case r => r } - def find_pos(v: Val, rs: List[Rexp]): Int = (rs, v) match{ + def find_pos(v: Val, rs: List[Rexp]): Int = (v, rs) match{ case (Right(v), r::Nil) => 1 case (Left(v), r::rs) => 0 case (Right(v), r::rs) => find_pos(v, rs) + 1 case (v, _) => 0 } - def remove(v: Val, rs: List[Rexp]) : Val = (rs,v) match {//remove the outmost layer of ALTS's Left and Right + def remove(v: Val, rs: List[Rexp]) : Val = (v,rs) match {//remove the outmost layer of ALTS's Left and Right case (Right(v), r::Nil) => v case (Left(v), r::rs) => v case (Right(v), r::rs) => remove(v, rs) } - def simple_end(v: Value): Boolean = v match { + def simple_end(v: Val): Boolean = v match { case Left(v) => return false case Right(v) => return simple_end(v) case v => return true } - def isend(v: Val, rs: List[Rexp], position: Int): Boolean = { + def isend(v: Val, rs: List[ARexp], position: Int): Boolean = { val rsbh = rs.slice(position, rs.length) val out_end = if(flats(rsbh) == Nil) true else false val inner_end = simple_end(v) inner_end && out_end } - def get_coat(v: Val, rs: List[Rexp], vs: Val): Val = (rs, v) match{//the dual operation of remove(so-called by myself) + def get_coat(v: Val, rs: List[Rexp], vs: Val): Val = (v, rs) match{//the dual operation of remove(so-called by myself) case (Right(v), r::Nil) => Right(vs) case (Left(v), r::rs) => Left(vs) case (Right(v), r::rs) => Right(get_coat(v, rs, vs)) @@ -479,6 +479,7 @@ case 0 => v case i => coat(Right(v), i - 1) } + /* def bsimp2(r: ARexp, v: Val): (ARexp, Val => Val) = (r,v) match{ case (ASEQ(bs1, r1, r2), v) => (bsimp2(r1), bsimp2(r2)) match { case ((AZERO, _), (_, _) )=> (AZERO, undefined) @@ -510,7 +511,7 @@ } //case ASTAR(bs, r) => ASTAR(bs, bsimp(r)) case r => r - } + }*/ def super_bsimp(r: ARexp): ARexp = r match { case ASEQ(bs1, r1, r2) => (super_bsimp(r1), super_bsimp(r2)) match { case (AZERO, _) => AZERO diff -r cd0ceaf89c1d -r c51178fa85fe slides01.tex --- a/slides01.tex Sun May 05 22:02:29 2019 +0100 +++ b/slides01.tex Wed May 08 22:09:59 2019 +0100 @@ -3,7 +3,7 @@ \usepackage{./graph} \usepackage{./langs} \usepackage{./data} - +\usepackage{changepage} \hfuzz=220pt \lstset{language=Scala, @@ -82,7 +82,78 @@ 60000 43.0327746 \end{filecontents} +\begin{filecontents}{re-usize.data} +1 16 +2 33 +3 63 +4 108 +5 181 +6 297 +7 484 +8 785 +9 1271 +10 2056 +11 3325 +12 5377 +13 8696 +14 14065 +15 22751 +16 36804 +17 59541 +18 96329 +19 155852 +20 252161 +21 407991 +22 660128 +23 1068093 +24 1728193 +25 2796256 +26 4524417 +27 7320639 +\end{filecontents} +\begin{filecontents}{re-ssize.data} +1 12 +2 19 +3 19 +4 19 +5 19 +6 19 +7 19 +8 19 +9 19 +10 19 +11 19 +12 19 +13 19 +14 19 +15 19 +16 19 +17 19 +18 19 +19 19 +20 19 +21 19 +22 19 +23 19 +24 19 +25 19 +26 19 +27 19 +28 19 +29 19 +30 19 +31 19 +32 19 +33 19 +34 19 +35 19 +36 19 +37 19 +38 19 +39 19 +40 19 +\end{filecontents} \begin{document} @@ -96,9 +167,9 @@ \begin{frame}[t] \frametitle{% \begin{tabular}{@ {}c@ {}} - \\[-3mm] - \LARGE Compilers and \\[-1mm] - \LARGE Formal Languages (1)\\[-3mm] + \\[-1mm] + \LARGE Fast Regular Expression \\[-1mm] + \LARGE Matching Using Derivatives\\[-3mm] \end{tabular}} \begin{center} @@ -110,18 +181,46 @@ \normalsize \begin{center} \begin{tabular}{ll} - Email: & christian.urban at kcl.ac.uk\\ - Office: & N\liningnums{7.07} (North Wing, Bush House)\\ - Slides: & KEATS + %Email: & christian.urban at kcl.ac.uk\\ + %Office: & N\liningnums{7.07} (North Wing, Bush House)\\ + %Slides: & KEATS + Student: & Chengsong Tan\\ + Supervisor: & Christian Urban \\ + Date: & 2019/5/10 \end{tabular} \end{center} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame}[t] -\frametitle{Why Study Compilers?} +\frametitle{Regular Expressions} + +Their inductive definition:\\ +\hspace{10pt} +\vspace{100pt} + +\begin{textblock}{6}(1.5,3.5) + \begin{tabular}{@ {}rrl@ {\hspace{13mm}}l} + \bl{$r$} & \bl{$::=$} & \bl{$\ZERO$} & nothing\\ + & \bl{$\mid$} & \bl{$\ONE$} & empty string / \pcode{""} / $[]$\\ + & \bl{$\mid$} & \bl{$c$} & character\\ + & \bl{$\mid$} & \bl{$r_1 + r_2$} & alternative / choice\\ + & \bl{$\mid$} & \bl{$r_1 \cdot r_2$} & sequence\\ + & \bl{$\mid$} & \bl{$r^*$} & star (zero or more)\\ + \end{tabular} + \end{textblock} + + \begin{itemize} +\item { Formalized by Stephen Coles Kleene in 1950s} +\item {\bf What could be possibly interesting?} + \end{itemize} +\end{frame} + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\iffalse +\begin{frame}[t] +\frametitle{Regular Expressions} John Regehr {\small(Univ.~Utah, LLVM compiler hacker)}\smallskip\\ @@ -162,9 +261,11 @@ \end{itemize}}} \end{frame} +\fi %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\iffalse \begin{frame}[c] \frametitle{Why Bother?} @@ -257,15 +358,24 @@ matching \texttt{[a?]\{n\}[a]\{n\}} and \texttt{(a*)*b} against $\underbrace{\texttt{a}...\texttt{a}}_n$ \end{frame} +\fi -\begin{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +\begin{frame}[c] +\frametitle{Catastrophic Backtracking} + +\begin{columns} \begin{column}{.5\textwidth} + \begin{tikzpicture} \begin{axis}[ xlabel={$n$}, - x label style={at={(1.05,0.0)}}, + x label style={at={(1.07,0.0)}}, ylabel={time in secs}, - y label style={at={(0.06,0.5)}}, + %y label style={at={(0.06,0.5)}}, enlargelimits=false, xtick={0,5,...,30}, xmax=33, @@ -273,20 +383,21 @@ ytick={0,10,...,40}, scaled ticks=false, axis lines=left, - width=6cm, - height=4.5cm, + width=5cm, + height=4cm, legend entries={Python, Java 8}, legend pos=north west] \addplot[blue,mark=*, mark options={fill=white}] table {re-python2.data}; \addplot[cyan,mark=*, mark options={fill=white}] table {re-java.data}; \end{axis} \end{tikzpicture} + \begin{tikzpicture} \begin{axis}[ xlabel={$n$}, - x label style={at={(1.05,0.0)}}, + x label style={at={(1.07,0.0)}}, ylabel={time in secs}, - y label style={at={(0.06,0.5)}}, + %y label style={at={(0.06,0.5)}}, %enlargelimits=false, %xtick={0,5000,...,30000}, xmax=65000, @@ -294,23 +405,58 @@ ytick={0,10,...,40}, scaled ticks=false, axis lines=left, - width=6cm, - height=4.5cm, + width=5cm, + height=4cm, legend entries={Java 9}, legend pos=north west] \addplot[cyan,mark=*, mark options={fill=white}] table {re-java9.data}; \end{axis} \end{tikzpicture} \end{column} +\end{columns}\bigskip +\center +matching \texttt{(a*)*b} +against $\underbrace{\texttt{a}...\texttt{a}}_n$ \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\begin{frame}[fragile] +\frametitle{Impact} + +\begin{itemize} +\item Network Traffic Analysis +\begin{itemize} +\item Snort: > 5 million downloads +\item Bro: > 10000 downloads +\item thousands of regexes +\item \alert{R}egular \alert{e}xpression \alert{D}enial \alert{o}f \alert{S}ervice (ReDoS)\medskip + +\end{itemize} + +\begin{verbatim} + Jan 2 00:53:19 talisker sshd: Received disconnect from 110.53.183.227: [preauth] + Jan 2 00:58:31 talisker sshd: Received disconnect from 110.53.183.252: [preauth] + Jan 2 01:01:28 talisker sshd: Received disconnect from 221.194.47.236: [preauth] + Jan 2 01:03:59 talisker sshd: Received disconnect from 110.53.183.228: [preauth] + Jan 2 01:06:53 talisker sshd: Received disconnect from 221.194.47.245: [preauth] + ... +\end{verbatim} + + +\item Compilers: lexical analysis +\end{itemize} + +\end{frame} + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame}[c] \frametitle{Evil Regular Expressions} \begin{itemize} -\item \alert{R}egular \alert{e}xpression \alert{D}enial \alert{o}f \alert{S}ervice (ReDoS)\medskip +%\item \alert{R}egular \alert{e}xpression \alert{D}enial \alert{o}f \alert{S}ervice (ReDoS)\medskip \item Evil regular expressions\medskip \begin{itemize} \item \bl{$(a^{?\{n\}}) \cdot a^{\{n\}}$} @@ -318,584 +464,296 @@ \item \bl{$([a$\,-\,$z]^+)^*$} \item \bl{$(a + a \cdot a)^*$} \item \bl{$(a + a^?)^*$} +\item \bl{$\^(.*?,)\{11\}P$} +\item \bl{$.*?.*?.*?.*?.*?]*>.*?.*?$} +\end{itemize} + +\item Pearl Compatible Regular Expression(PCRE) \bl{$(r) \backslash 1$} \end{itemize} -\item sometimes also called \alert{catastrophic backtracking} -\item this is a problem for \alert{N}etwork \alert{I}ntrusion - \alert{D}etection systems, StackExchange, Atom editor -\item \url{https://vimeo.com/112065252} +\end{frame} + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +\begin{frame}[c] +\frametitle{A Concrete Example} +\begin{adjustwidth*}{}{-1.2cm} +\resizebox{13cm}{4cm}{ + + \begin{tikzpicture}[shorten >=1pt,node distance=2cm,on grid,auto] + \node[state,initial] (q_0) {$0$}; + \node[state] (q_1) [right = of q_0] {$1$}; + \node[state] (q_2) [right=of q_1] {$2$}; + \node (q_dots1) [right = of q_2] {$\cdots$}; + \node [state] (q_n) [right = of q_dots1] {$n$}; + \node [state] (q_n1) [right = of q_n] {$n+1$}; + \node[state] (q_n2) [right=of q_n1] {$n+2$}; + \node[state,accepting] (q_n3) [right=of q_n2] {$n+3$}; + + \path[->] + (q_0) edge [loop above] node {$*$} (q_0) + (q_0) edge node {$a$} (q_1) + (q_1) edge node {$*$} (q_2) + (q_2) edge node {$*$} (q_dots1) + (q_dots1) edge node{$*$} (q_n) + (q_n) edge node{$*$} (q_n1) + (q_n1) edge node{$*$} (q_n2) + (q_n2) edge node{$*$} (q_n3); + +\draw [decorate,decoration={brace,amplitude=10pt,mirror,raise=10pt},yshift=0pt] +(q_2.south west) -- (q_n1.south east) node [black,midway,yshift = -2cm] {\footnotesize n states}; +%\draw [decorate,decoration={brace,amplitude=10pt,mirror,raise=4pt},yshift=0pt] +%(3.5,0.65) -- (3.5,6.5) node [black,midway,xshift=0.8cm] {\footnotesize +%$P_2$}; +\end{tikzpicture} +} +\end{adjustwidth*} + +\begin{itemize} +\item +NFA accepting Regex $.*a.{n}bc$ +\item +Matching the string aaaaaaaaaaaaaaa.....abc +\end{itemize} +\end{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\begin{frame}[c] +\frametitle{Brzozowski Derivative} + +\begin{itemize} +\item Brzozowski invented in his 1964 Phd thesis +\item Intuition: Chopping off the first character + +\begin{center} +\bl{$A \backslash c \dn \{ s \;|\; c\!::\!s \in A\}$ } +\end{center} +\item +For \bl{$A = \{\textit{foo}, \textit{bar}, \textit{frak}\}$} then + +\begin{center} +\bl{\begin{tabular}{l@{\hspace{2mm}}c@{\hspace{2mm}}l} +$A \backslash f $ & $=$ & $\{\textit{oo}, \textit{rak}\}$\\ +$A \backslash b $ & $=$ & $\{\textit{ar}\}$\\ +$A \backslash a $ & $=$ & $\{\}$\pause +\end{tabular}} +\end{center} +\item +\begin{tabular}{rp{4cm}} +\bl {$r \,matches \,s=c_1c_2...c_n$} +\bl{$\Leftrightarrow$} \bl{$c_1c_2...c_n \in L(r)$} \bl{$\Leftrightarrow$}\\ + \bl{$c_2...c_n \in L(r) \backslash c_1$}\\ +\bl{$\Leftrightarrow$} \bl{$\cdots$}\\ +\bl{$\Leftrightarrow$} \bl{$[] \in ((L(r)\backslash c_1) \backslash c_2)\cdots\backslash c_n$} +\end{tabular} + \end{itemize} \end{frame} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +\begin{frame}[c] +\frametitle{Previous Example} + +\begin{center} +\begin{tikzpicture} + \begin{axis}[ + xlabel={$n$}, + x label style={at={(1.09,-0.15)}}, + ylabel={time in secs}, + scaled x ticks=false, + enlargelimits=false, + xtick distance=10000, + xmax=44000, + ytick={0,10,...,30}, + ymax=35, + axis lines=left, + width=7cm, + height=3.5cm, + legend entries={Java \liningnums{9}+}, + legend pos=north west, + legend cell align=left] +\addplot[blue,mark=square*,mark options={fill=white}] table {re-java9.data}; +\end{axis} +\end{tikzpicture} +\end{center} + +\begin{center} +\begin{tikzpicture} + \begin{axis}[ + xlabel={$n$}, + x label style={at={(1.09,0.0)}}, + ylabel={time in secs}, + scaled x ticks=false, + xtick distance=2000000, + enlargelimits=false, + xmax=6400000, + ytick={0,10,...,30}, + ymax=35, + axis lines=left, + width=7cm, + height=3.5cm, + legend entries={Simple Scala}, + legend pos=north west, + legend cell align=left] +%\addplot[green,mark=square*,mark options={fill=white}] table {re2a.data}; +\addplot[black,mark=square*,mark options={fill=white}] table {re3a.data}; +\end{axis} +\end{tikzpicture} +\end{center} + +Regex: \bl{$(a^*)^* \cdot b$} \space\space\space\space\space\space +Strings of the form \bl{$\underbrace{\,a\ldots a\,}_{n}$} + +\end{frame} + %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{The Goal of this Module} +\begin{frame}[t] +\frametitle{Optimization} \begin{center} - \begin{tikzpicture}[scale=1, - node/.style={ - rectangle,rounded corners=3mm, - very thick,draw=black!50,minimum height=18mm, minimum width=20mm, - top color=white,bottom color=black!20}] - - \node at (3.05, 1.8) {\Large\bf write a compiler}; - - \node (0) at (-2.3,0) {}; - \node [above=5mm of 0] - {\makebox[0mm]{\footnotesize - \begin{tabular}{@{}l@{}}input\\[-1mm]program\end{tabular}}}; - - \node (A) at (0,0) [node] {}; - \node [below right] at (A.north west) {lexer}; - - \node (B) at (3,0) [node] {}; - \node [below right=1mm] at (B.north west) {\mbox{}\hspace{-1mm}parser}; - - \node (C) at (6,0) [node] {}; - \node [below right] at (C.north west) {\mbox{}\hspace{-1mm}code gen}; - - \node (1) at (8.4,0) {}; - \node [above=5mm of 1] - {\makebox[0mm]{\footnotesize - \begin{tabular}{@{}r@{}}binary\\[-1mm]code\end{tabular}}}; - - \draw [->,line width=4mm] (0) -- (A); - \draw [->,line width=4mm] (A) -- (B); - \draw [->,line width=4mm] (B) -- (C); - \draw [->,line width=4mm] (C) -- (1); - \end{tikzpicture} - \end{center} - -\only<2,3,4>{ -\begin{textblock}{1}(1,2.1) -\begin{bubble}[9.8cm] -\normalsize -lexer input: a string\smallskip\\ -\hspace{5mm}\code{"read(n);"}\medskip\\ -lexer output: a sequence of tokens\smallskip\\ -\hspace{5mm}\code{key(read) lpar id(n) rpar semi} -\end{bubble} -\end{textblock}} - -\only<3,4>{ -\begin{textblock}{1}(6,7.8) -\begin{tabular}{c} -\includegraphics[scale=0.2]{rosetta.jpg}\\[-2mm] -\footnotesize lexing $\Rightarrow$ recognising words (Stone of Rosetta) -\end{tabular} -\end{textblock}} - -\only<4>{ -\begin{textblock}{1}(0.5,12)\small -\begin{tabular}{l@{}c@{}l} - \pcode{if} & $\;\Rightarrow\;$ & keyword\\ - \pcode{iffoo} & $\;\Rightarrow\;$ & identifier\\ -\end{tabular} -\end{textblock}} +\begin{tikzpicture} +\begin{semilogyaxis}[ + xlabel={$n$}, + x label style={at={(1.05,0.0)}}, + ylabel={regex size}, + enlargelimits=false, + xtick={1,4,...,30}, + xmax=33, + %ytick={0, 10,...,100}, + scaled ticks=false, + axis lines=left, + width=9cm, + height=4.5cm, + legend entries={Simple Scala}, + legend pos= south east, + legend cell align=left +] +\addplot[black,mark=square*, mark options={fill=white}] table {re-usize.data}; +%\addplot[brown,mark=pentagon*, mark options={fill=white}] table {re-ssize.data}; +%\addplot[red,mark=triangle*,mark options={fill=white}] table {re1.data}; +%\addplot[green,mark=square*,mark options={fill=white}] table {re2.data}; +\end{semilogyaxis} +\end{tikzpicture} +\end{center} +Regex: \bl{$(a+aa)^* \cdot b$} \space\space\space\space\space\space +Strings of the form \bl{$\underbrace{\,a\ldots a\,}_{n}$}\\ +\begin{itemize} +\item +Solution: Simplification%(Sulzmann \& Lu) +\begin{itemize} +\item $r+(r+s) = r+r+s = r+s$ +\item $1 \cdot r= r$ +\end{itemize} +\end{itemize} +\end{frame} +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\begin{frame}[t] +\frametitle{Optimization} -\only<5>{ -\begin{textblock}{1}(1,1.5) -\begin{bubble}[8.5cm] -\normalsize -parser input: a sequence of tokens\smallskip\\ - -{\small\hspace{5mm}\code{key(read) lpar id(n) rpar semi}}\smallskip\\ - -parser output: an abstract syntax tree\smallskip\\ -\footnotesize -\hspace{2cm}\begin{tikzpicture} - \node {\code{read}} - child {node {\code{lpar}}} - child {node {\code{n}}} - child {node {\code{rpar}}}; -\end{tikzpicture} -\end{bubble} -\end{textblock}} +Regex: \bl{$(a+aa)^* \cdot b$} \space\space\space\space\space\space +Strings of the form \bl{$\underbrace{\,a\ldots a\,}_{n}$} -\only<6,7>{ -\begin{textblock}{1}(1,1.5) -\begin{bubble}[4cm] -\normalsize -code generator:\smallskip\\ -\hspace{5mm}\code{istore 2}\\ -\hspace{5mm}\code{iload 2}\\ -\hspace{5mm}\code{ldc 10}\\ -\hspace{5mm}\code{isub}\\ -\hspace{5mm}\code{ifeq Label2}\\ -\hspace{5mm}\code{iload 2}\\ -\hspace{5mm}\code{...}\\ -\end{bubble} -\end{textblock}} - -\only<7>{ -\begin{textblock}{6}(8.4,7) -\begin{bubble}[5cm] -\mbox{\begin{tikzpicture}[scale=0.58,rounded corners=0mm] -\begin{axis}[axis x line=bottom, axis y line=left, ylabel=secs, - xlabel=n, - enlargelimits=0.05, - ybar interval=0.7, legend style=small] -\addplot file {interpreted2.data}; -\addplot file {compiled2.data}; -%\legend{interpreted, compiled} +\begin{center} +\begin{tikzpicture} +\begin{axis}[ + xlabel={$n$}, + x label style={at={(1.05,0.0)}}, + ylabel={regex size}, + enlargelimits=false, + xtick={1,4,...,30}, + xmax=33, + %ytick={0, 10,...,100}, + scaled ticks=false, + axis lines=left, + width=9cm, + height=4.5cm, + legend entries={Simplification Applied}, + legend pos= south east, + legend cell align=left +] +%\addplot[black,mark=square*, mark options={fill=white}] table {re-usize.data}; +\addplot[black,mark=triangle*, mark options={fill=white}] table {re-ssize.data}; +%\addplot[red,mark=triangle*,mark options={fill=white}] table {re1.data}; +%\addplot[green,mark=square*,mark options={fill=white}] table {re2.data}; \end{axis} -\end{tikzpicture}} -\end{bubble} -\end{textblock}} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{The Acad.~Subject is Mature} - +\end{tikzpicture} +\end{center} \begin{itemize} -\item Turing Machines, 1936 -\item Regular Expressions, 1956\\ -\item The first compiler for COBOL, 1957\\ (Grace Hopper) -\item But surprisingly research papers are still published nowadays\\ -\item ``Parsing: The Solved Problem That Isn't'' +\item +Lexer? Not just matcher +\begin{itemize} +\item +Bit-Coded Regular Expression Parsing (Lasse Nielsen, Fritz Henglein 2011) +\item +Bit-Coded Regular Expression Parsing with Simplification (Sulzmann and Lu 2014) \end{itemize} -\begin{flushright} -\includegraphics[scale=0.3]{hopper.jpg}\\ -\footnotesize\textcolor{gray}{Grace Hopper} -\end{flushright} +\end{itemize} +\end{frame} -\begin{flushright} -\mbox{}\\[-6mm] -{\footnotesize\textcolor{gray}{(she made it to David Letterman's Tonight Show,\\[-2mm] - \url{http://www.youtube.com/watch?v=aZOxtURhfEU})}} -\end{flushright} -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Lectures 1 - 5} -transforming strings into structured data\\[10mm] - -{\LARGE\bf Lexing} {\hfill{}based on regular expressions}\medskip\\ -\hspace{5mm}(recognising ``words'')\\[6mm] - -{\LARGE\bf Parsing}\medskip\\ -\hspace{5mm}(recognising ``sentences'') - -\begin{textblock}{1}(10,9.1) -\begin{tabular}{c} -\includegraphics[scale=0.1]{rosetta.jpg}\\[-2mm] -\footnotesize Stone of Rosetta -\end{tabular} -\end{textblock} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{frame}[t] -\frametitle{Familiar Regular Expr.} -\small -\begin{center} -\texttt{[a-z0-9\_$\backslash{}$.-]+ @ [a-z0-9$\backslash{}$.-]+ . [a-z$\backslash{}$.]\{2,6\}} -\end{center}\smallskip - -\begin{center} -\begin{tabular}{@{}lp{8.5cm}@{}} -\pcode{re*} & matches 0 or more times\\ -\pcode{re+} & matches 1 or more times\\ -\pcode{re?} & matches 0 or 1 times\\ -\pcode{re\{n\}} & matches exactly \pcode{n} number of times\\ -\pcode{re\{n,m\}} & matches at least \pcode{n} and at most {\tt m} times\\ -\pcode{[...]} & matches any single character inside the brackets\\ -\pcode{[^...]} & matches any single character not inside the -brackets\\ -\pcode{a-z A-Z} & character ranges\\ -\pcode{\\d} & matches digits; equivalent to \pcode{[0-9]}\\ -\pcode{.} & matches every character except newline\\ -\pcode{(re)} & groups regular expressions and remembers -the matched text -\end{tabular} -\end{center} +\frametitle{Ongoing Work} -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Today} - -\begin{itemize} -\item While the ultimate goal is to implement a small compiler for the JVM - \ldots\bigskip -\end{itemize} - -Let's start with: +\begin{tikzpicture} +\begin{semilogyaxis}[ + xlabel={$n$}, + x label style={at={(1.05,0.0)}}, + ylabel={regex size}, + enlargelimits=false, + xtick={1,4,...,30}, + xmax=33, + %ytick={0, 10,...,100}, + scaled ticks=false, + axis lines=left, + width=9cm, + height=4.5cm, + legend entries={Naive, Simp}, + legend pos= north west, + legend cell align=left +] +\addplot[black,mark=square*, mark options={fill=white}] table {re-usize.data}; +\addplot[black,mark=triangle*, mark options={fill=white}] table {re-ssize.data}; +%\addplot[red,mark=triangle*,mark options={fill=white}] table {re1.data}; +%\addplot[green,mark=square*,mark options={fill=white}] table {re2.data}; +\end{semilogyaxis} +\end{tikzpicture} \begin{itemize} -\item a web-crawler -\item an email harvester -%\item \textcolor{gray}{(a web-scraper)} -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +\item +Correctness of Sulzmann \& Lu's algorithm -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{A Web-Crawler} - -\mbox{}\\[10mm] - -\begin{enumerate} -\item given an URL, read the corresponding webpage -\item extract all links from it -\item call the web-crawler again for all these links -\end{enumerate} - +\item +Size Bound $O(n^2t^2)$ of Dervatives (1995 Antimirov "Partial Derivative") +\item +More radical simplifications. +\item +Extend the algorithm to back-references. +\end{itemize} \end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{A Web-Crawler} - -\mbox{}\\[10mm] - - -\begin{enumerate} -\item given an URL, read the corresponding webpage -\item if not possible print, out a problem -\item if possible, extract all links from it -\item call the web-crawler again for all these links -\end{enumerate}\bigskip\pause - -\small (we need a bound for the number of recursive calls) - -\small (the purpose is to check all links on my own webpage) -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] - -\begin{textblock}{1}(2,5) -\begin{tabular}{c} -\includegraphics[scale=0.15]{servers.png}\\[-2mm] -\small Server -\end{tabular} -\end{textblock} - -\begin{textblock}{1}(5.6,4) - \begin{tikzpicture}[scale=1.1] - \draw[white] (0,1) node (X) {}; - \draw[white] (2,1) node (Y) {}; - \draw[white] (0,0) node (X1) {}; - \draw[white] (2,0) node (Y1) {}; - \draw[white] (0,-1) node (X2) {}; - \draw[white] (2,-1) node (Y2) {}; - \draw[red, <-, line width = 2mm] (X) -- (Y); - \node [inner sep=5pt,label=above:\textcolor{black}{GET request}] at ($ (X)!.5!(Y) $) {}; - \draw[red, ->, line width = 2mm] (X1) -- (Y1); - \node [inner sep=5pt,label=above:\textcolor{black}{webpage}] at ($ (X1)!.5!(Y1) $) {}; - \draw[red, <-, line width = 2mm] (X2) -- (Y2); - \node [inner sep=7pt,label=above:\textcolor{black}{POST data}] at ($ (X2)!.5!(Y2) $) {}; - \end{tikzpicture} -\end{textblock} -\begin{textblock}{1}(9,5.5) -\begin{tabular}{c} -\includegraphics[scale=0.15]{laptop.png}\\[-2mm] -\small Browser -\end{tabular} -\end{textblock} -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - - - - - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{A Regular Expression} - -\begin{itemize} -\item \ldots{} is a pattern or template for specifying strings -\end{itemize}\bigskip - -\begin{center} -\only<1>{\scode{"https?://[^"]*"}}% -\only<2>{\scode{""""https?://[^"]*"""".r}} -\end{center}\bigskip\bigskip - -matches for example\smallskip\\ -\hspace{2mm}\code{"http://www.foobar.com"}\\ -\hspace{2mm}\code{"https://www.tls.org"}\smallskip\\ - -but not\smallskip\\ -\hspace{2mm}\code{"http://www."foo"bar.com"}\\ - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Finding Operations in Scala} - -{\bf\code{rexp.findAllIn(string)}}\medskip - -returns a list of all (sub)strings that match the -regular expression -\bigskip\bigskip - - -{\bf\code{rexp.findFirstIn(string)}}\medskip - -returns either - -\begin{itemize} -\item \code{None} if no (sub)string matches or -\item \code{Some(s)} with the first (sub)string -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{Regular Expressions} - -Their inductive definition: -\begin{textblock}{6}(2,7.5) - \begin{tabular}{@ {}rrl@ {\hspace{13mm}}l} - \bl{$r$} & \bl{$::=$} & \bl{$\ZERO$} & nothing\\ - & \bl{$\mid$} & \bl{$\ONE$} & empty string / \pcode{""} / $[]$\\ - & \bl{$\mid$} & \bl{$c$} & character\\ - & \bl{$\mid$} & \bl{$r_1 + r_2$} & alternative / choice\\ - & \bl{$\mid$} & \bl{$r_1 \cdot r_2$} & sequence\\ - & \bl{$\mid$} & \bl{$r^*$} & star (zero or more)\\ - \end{tabular} - \end{textblock} - - - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -%\begin{frame}[t] -%\frametitle{Regular Expressions} -% -%\small -%In Scala:\bigskip -% -%\footnotesize -%\lstinputlisting{../progs/app51.scala} -% -% -%\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{Strings} - -\ldots are lists of characters. For example \code{"hello"} - -\begin{center} -\bl{$[h, e, l, l, o]$} or just \bl{$hello$} -\end{center} - -the empty string: \bl{$[]$} or \bl{\pcode{""}}\bigskip\\ - -the concatenation of two strings: - -\begin{center} -\bl{$s_1 \,@\, s_2$} -\end{center} - -\bl{\textit{foo $@$ bar = foobar}, \textit{baz $@\, []$ = baz}} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Languages, Strings} - -\begin{itemize} -\item \alert{\bf Strings} are lists of characters, for example -\begin{center} -\bl{$[]$},\;\bl{$abc$} \hspace{2cm}(Pattern match: \bl{$c\!::\!s$}) -\end{center}\bigskip - - -\item A \alert{\bf language} is a set of strings, for example\medskip -\begin{center} -\bl{$\{[], hello, \textit{foobar}, a, abc\}$} -\end{center}\bigskip - -\item \alert{\bf Concatenation} of strings and languages - -\begin{center} -\begin{tabular}{rcl} -\bl{$\textit{foo}\;@\;bar$} & \bl{$=$} & \bl{$\textit{foobar}$}\medskip\\ -\bl{$A\;@\;B$} & \bl{$\dn$} & \bl{$\{ s_1\,@\,s_2 \;\mid\; s_1 \in A \wedge s_2 \in B\}$} -\end{tabular} -\end{center} - -%\item The \alert{\bf meaning} of a regular expression is a set of -% strings, or language. -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\mode{ -\begin{frame}[c] -\frametitle{\begin{tabular}{c}The Meaning of a\\[-2mm] - Regular Expression\end{tabular}} -\begin{textblock}{15}(1,4) - \begin{tabular}{rcl} - \bl{$L(\ZERO)$} & \bl{$\dn$} & \bl{$\{\}$}\\ - \bl{$L(\ONE)$} & \bl{$\dn$} & \bl{$\{[]\}$}\\ - \bl{$L(c)$} & \bl{$\dn$} & \bl{$\{[c]\}$}\\ - \bl{$L(r_1 + r_2)$} & \bl{$\dn$} & \bl{$L(r_1) \cup L(r_2)$}\\ - \bl{$L(r_1 \cdot r_2)$} & \bl{$\dn$} & \bl{$\{ s_1 \,@\, s_2 \;|\; s_1 \in L(r_1) \wedge s_2 \in L(r_2) \}$}\\ - \bl{$L(r^*)$} & \bl{$\dn$} & \onslide<4->{\bl{$\bigcup_{0 \le n} L(r)^n$}}\\ - \end{tabular}\bigskip - -\onslide<2->{ -\hspace{5mm}\bl{$L(r)^0 \;\dn\; \{[]\}$}\\ -\bl{$L(r)^{n+1} \;\dn\; L(r) \,@\, L(r)^n$}\hspace{9mm}\onslide<3->{\small\textcolor{gray}{(append on sets)}\\ -\small\hspace{5cm}\textcolor{gray}{$\{ s_1 @ s_2 \;|\; s_1\in L(r) \wedge s_2 \in L(r)^n \}$}} -} - \end{textblock} - -\end{frame}} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{The Meaning of Matching} - -\begin{bubble}[10cm] -\large\bf -A regular expression \bl{$r$} matches a string~\bl{$s$} -provided - -\begin{center} -\bl{$s \in L(r)$}\\ -\end{center} -\end{bubble}\bigskip\bigskip - -\ldots and the point of the next lecture is -to decide this problem as fast as possible (unlike Python, -Ruby, Java) - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Written Exam} - -\begin{itemize} -\item Accounts for 80\%.\bigskip - -\item The question ``\textit{Is this relevant for - the exam?}'' is very demotivating for the lecturer!\bigskip\\ - -\item Deal: Whatever is in the homework (and is not marked - ``\textit{optional}'') is relevant for the exam.\bigskip - -\item Each lecture has also a handout. There are also handouts about -notation and Scala. -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[t] -\frametitle{Coursework} - -\begin{itemize} -\item Accounts for 20\%. Two strands. Choose \alert{\bf one}!\bigskip -\end{itemize} - -\begin{columns}[t] -\begin{column}{.5\textwidth} -\underline{\bf Strand 1}\medskip -\begin{itemize} -\item four programming tasks: -\begin{itemize} -\item matcher (4\%, 12.10.) -\item lexer (5\%, 02.11.) -\item parser (5\%, 23.11.) -\item compiler (6\%, 14.12.) -\end{itemize} -\item in any lang.~you like,\\ but I want to see the code -\end{itemize} -\end{column} - -\hspace{-45pt}\vrule{}\hspace{10pt} -\begin{column}{.5\textwidth} -\underline{\bf Strand 2}\smallskip\begin{itemize} -\item one task: prove the correctness of a regular expression matcher in -the \underline{Isabelle} theorem prover -\item 20\%, submission on~14.12.\hspace{-5mm}\mbox{} -\end{itemize} -\end{column} -\end{columns}\medskip - -\small -\begin{itemize} -\item Solving more than one strand will {\bf not} give you more -marks. - -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% - -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% -\begin{frame}[c] -\frametitle{Lecture Capture} - -\begin{itemize} -\item Hope it works\ldots\pause actually no, it does not!\medskip\pause -\item It is important to use lecture capture wisely\\ (it is only the ``baseline''): -\begin{itemize} -\item Lecture recordings are a study and revision aid. -\item Statistically, there is a clear and direct link between attendance and - attainment: Students who do not attend lectures, do less well in exams. -\end{itemize} - -\item Attending a lecture is more than watching it online -- if you do not -attend, you miss out! - -\end{itemize} - -\end{frame} -%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%