The ENCOPLOT Similarity Measure for Automatic Detection of - PowerPoint PPT Presentation

The ENCOPLOT Similarity Measure for Automatic Detection of Plagiarism Cristian Grozea 1 Marius Nicolae Popescu 2 cristian.grozea@brainsignals.de Fraunhofer Institute FIRST – Berlin University of Bucharest Romania September 23, 2011 C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

I’ll be short... Thank you! . Our extended paper http://brainsignals.de/encsimTR.pdf C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Results External plagiarism, same language. ◮ 2009: 1 st ◮ 2010: 4 th (2 nd w. vers.2011) ◮ 2011: 2 nd (1 st ?) ◮ best score on the manual paraphrasing ◮ best recall on the non-translated corpus C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Encoplot and the Similarity Measure 350000 300000 250000 Suspicious Document Position 200000 150000 100000 50000 0 0 100000 200000 300000 400000 500000 600000 700000 Source Document Position C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Encoplot Features ◮ Guaranteed linear time – Dotplot is quadratic. ◮ Extremely fast highly optimized open-source implementation, for N-grams up to N=16, on 64 bit CPUs. Grozea et. al. (PAN 2009) C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

The Parallel Encoplot ◮ Open source, licensed under Apache APL http://code.google.com/p/parallel- encoplot/ ◮ Includes the parallelization with BSC SMPSs ◮ Scalable, tested on a machine with 256 cores HPC Europa2 - You can have that too! C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Ranking - 2010 1 Standard − ranking sources Standard − ranking destinations 0.9 Encoplot − global rank 0.8 0.7 0.6 Recall 0.5 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 7 Document pairs 6 x 10 C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Ranking - 2011 0.8 Standard − min rank Encoplot − min rank 0.7 0.6 0.5 Recall 0.4 0.3 0.2 0.1 0 5 6 10 10 Document pairs (logarithmic scale) C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Ranking - 2010 P-R 1 Standard − global rank Standard − min rank Standard − ranking sources 0.9 Standard − ranking destinations Encoplot − global rank Encoplot − min rank 0.8 0.7 0.6 Recall 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Precision C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Who’s the Thief? 7 x 10 5 6 5 Position in destination 4 3 2 1 0 0 0.5 1 1.5 2 2.5 3 Position in source x 10 5 Grozea and Popescu (CICLING 2010) – 75% C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Found anything useful to you? Thank you again! C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Reserve slides C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

2010 duplicates 350000 300000 250000 Suspicious Document Position 200000 150000 100000 50000 0 0 20000 40000 60000 80000 100000 120000 140000 Source Document Position C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

2011 Corpus Table: Results on 2011 Competition Data Subset Size Recall Precision F-score Granularity Plagdet score Entire corpus 49,621 0.34 0.81 0.48 1.22 0.42 No paraphrasing 976 0.90 0.84 0.86 1.02 0.85 Manual paraphras- 0.36 0.96 0.53 0.50 4,609 1.06 ing 0.58 Automatic low 19,779 0.90 0.71 1.27 0.60 Automatic high 19,115 0.08 0.64 0.14 1.19 0.13 Manual translation 433 0.08 0.25 0.12 1.01 0.12 Automatic transla- 4,709 0.23 0.40 0.29 1.07 0.28 tion C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Other Bits 2011 no obfuscation: 976 = 1.97% of 49 621 total (vs. 40%). The 18% includes about 10 000 from the intrinsic corpus. 2010 multiplicity problem: Maximum multiplicity =17 (source 8584, suspicious 3283). 55 723 external plagiarism instances 10 694 of which with multiplicity ≥ 2 (20% of total). 3 483 with multiplicity at least 3. Being able to handle multiplicity up to 4 would leave out only 506 instances. 2010 performance: plagdet score 0.72 (first team - 0.78), with recall 0.66 and precision 0.86, without handling the translated cases (14%). C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

N-Gram Coincidence Plot Algorithm Input: Sequences A and B to compare Output: list (x,y) of positions in A, respectively B, where there is exactly the same N-gram Steps 1. Extract the N-grams from A and B 2. Sort these two lists of N-grams 3. Compare these lists in a modified mergesort algorithm. Whenever the two smallest N-grams are the equal, output the position in A and the one in B. C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Small example A=abcabd B=xabdy Encoplot pairs Dotplot pairs 1 2 ab 1 2 ab N=2 4 2 ab 5 4 bd 5 4 bd Encoplot pairs Dotplot pairs N=3 4 2 abd 4 2 abd C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Fast Radix Sort for N-Grams for(i,NN)ix[i]=i; //radix sort, the input is x, // the output rank is ix for(k,RANGE)counters[k]=0; for(i,NN)counters[*(x+i)]++; for(j,DEPTH){ int ofs=j;//low endian t_int sp=0; for(k,RANGE){ startpos[k]=sp; sp+=counters[k]; } for(i,NN){ unsigned char c=x[ofs+ix[i]]; ox[startpos[c]++]=ix[i]; } memcpy(ix,ox,NN*sizeof(ix[0])); //update counters if(j<DEPTH-1){ counters[*pout++]--; counters[*pin++]++; } } C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

◮ Who’s the Thief? Automatic Detection of the Direction of Plagiarism, C.Grozea and M.Popescu, CICLING 2010 , LNCS 6008, DOI 10.1007/978-3-642-12116-6, 2010 ◮ ENCOPLOT: Pairwise Sequence Matching in Linear Time Applied to Plagiarism Detection, C.Grozea, C.Gehl, and M.Popescu – In Proceedings of the 3rd PAN Workshop. Uncovering Plagiarism, Authorship and Social Software Misuse, San Sebastian, Spain, 2009. Universidad Politecnica de Valencia 2009 ◮ Encoplot – Performance in the Second International Plagiarism Detection Challenge, C. Grozea and M. Popescu, Lab Report for PAN at CLEF 2010 ◮ Plagiarism Detection with State of the Art Compression Programs, C.Grozea Report CDMTCS-247, Centre for Discrete Mathematics and Theoretical Computer Science, University of Auckland, Auckland, New Zealand, 2004. C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania

Self-plagiarism 9 x 10 5 8 Suspicious Document Position 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 Source Document Position x 10 5 C.Grozea, M.Popescu: ENCOPLOT measure Fraunhofer Institute FIRST – Berlin, University of Bucharest Romania