Using a Variety of n-Grams for the Detection of Different Kinds of Plagiarism Notebook for PAN at CLEF 2013

A text can be plagiarised in different ways. The text may be copied and pasted word by word, parts of the text may be changed, or the whole text may be summarised into one or two lines. Different kinds of plagiarism require different strategies to detect them. But rarely do we know beforehand what type of plagiarism we are dealing with. In this paper we present a system that can detect verbatim plagiarism and obfuscated plagiarism with similar accuracy. Our system uses three different types of n-grams: stopword n-grams, n-grams with at least one named entity, and all words n-grams. After detecting and merging the detections to obtain passages, the system finds new detections incrementally based on the idea that the passages on the vicinity of plagiarised passages are more likely to be plagiarised. The system performs well on verbatim as well as obfuscated plagiarism cases.