Detecting code clones has many software engineering applications. Existing approaches either do not scale to large code bases or are not robust against minor code modifications. In this paper, we present an efficient algorithm for identifying similar subtrees and apply it to tree representations of source code. Our algorithm is based on a novel characterization of subtrees with numerical vectors in the Euclidean space \mathbb{R}^n and an efficient algorithm to cluster these vectors w.r.t. the Euclidean distance metric. Subtrees with vectors in one cluster are considered similar. We have implemented our tree similarity algorithm as a clone detection tool called DECKARD and evaluated it on large code bases written in C and Java including the Linux kernel and JDK. Our experiments show that DECKARD is both scalable and accurate. It is also language independent, applicable to any language with a formally specified grammar.

/pdf/deckard-scalable-and-accurate-tree-based-detection-of-code-37e0p0rfkn.pdf

DECKARD: Scalable and Accurate Tree-Based Detection of Code Clones

https://www.cs.usask.ca/~croy/papers/2009/RCK_SCP_Clones.pdf

Comparison and evaluation of code clone detection techniques and tools: A qualitative approach

Many techniques for detecting duplicated source code (software clones) have been proposed in the past. However, it is not yet clear how these techniques compare in terms of recall and precision as well as space and time requirements. This paper presents an experiment that evaluates six clone detectors based on eight large C and Java programs (altogether almost 850 KLOC). Their clone candidates were evaluated by one of the authors as an independent third party. The selected techniques cover the whole spectrum of the state-of-the-art in clone detection. The techniques work on text, lexical and syntactic information, software metrics, and program dependency graphs.

/pdf/comparison-and-evaluation-of-clone-detection-tools-4951gpp7yk.pdf

Comparison and Evaluation of Clone Detection Tools

Code duplication or copying a code fragment and then reuse by pasting with or without any modiflcations is a well known code smell in software maintenance. Several studies show that about 5% to 20% of a software systems can contain duplicated code, which is basically the results of copying existing code fragments and using then by pasting with or without minor modiflcations. One of the major shortcomings of such duplicated fragments is that if a bug is detected in a code fragment, all the other fragments similar to it should be investigated to check the possible existence of the same bug in the similar fragments. Refactoring of the duplicated code is another prime issue in software maintenance although several studies claim that refactoring of certain clones are not desirable and there is a risk of removing them. However, it is also widely agreed that clones should at least be detected. In this paper, we survey the state of the art in clone detection research. First, we describe the clone terms commonly used in the literature along with their corresponding mappings to the commonly used clone types. Second, we provide a review of the existing clone taxonomies, detection approaches and experimental evaluations of clone detection tools. Applications of clone detection research to other domains of software engineering and in the same time how other domain can assist clone detection research have also been pointed out. Finally, this paper concludes by pointing out several open problems related to clone detection research.

/pdf/a-survey-on-software-clone-detection-research-3hmh7abinb.pdf

A Survey on Software Clone Detection Research

Context Reusing software by means of copy and paste is a frequent activity in software development. The duplicated code is known as a software clone and the activity is known as code cloning. Software clones may lead to bug propagation and serious maintenance problems. Objective This study reports an extensive systematic literature review of software clones in general and software clone detection in particular. Method We used the standard systematic literature review method based on a comprehensive set of 213 articles from a total of 2039 articles published in 11 leading journals and 37 premier conferences and workshops. Results Existing literature about software clones is classified broadly into different categories. The importance of semantic clone detection and model based clone detection led to different classifications. Empirical evaluation of clone detection tools/techniques is presented. Clone management, its benefits and cross cutting nature is reported. Number of studies pertaining to nine different types of clones is reported. Thirteen intermediate representations and 24 match detection techniques are reported. Conclusion We call for an increased awareness of the potential benefits of software clone management, and identify the need to develop semantic and model clone detection techniques. Recommendations are given for future research.

http://romisatriawahono.net/lecture/rm/survey/software%20engineering/Software%20Construction/Rattan%20-%20Software%20Clone%20Detection%20-%202013.pdf

Software clone detection: A systematic review

In this paper we describe a new approach for the detection of clones in source code, which is inspired by the concept of frequent itemsets from data mining. The source code is represented as an abstract syntax tree in XML. Currently, such XML representations exist for instance for Java, C++, or PROLOG. Our approach is very flexible; it can be configured easily to work with multiple programming languages

Clone detection in source code by frequent itemset techniques

syntax trees (ASTs) are known from compiler construction where they build the intermediate data format which is passed from the analytic front-end to the synthetic back-end. In model driven software development ASTs are used as a model of the source code. The object management group (OMG) has issued a request for proposals for AST models. Various levels of abstraction can be introduced. ASTs can be used for program analysis and for program transformation. In this paper we present an eclipse based representation framework for ASTs.

Abstract Syntax Trees - and their Role in Model Driven Software Development

The paper presents an online Java course consisting of a tutorial that provides a high level of interaction and an assessment tool that analyses the code and enables the students to run a suite of predefined tests.The hypertext tutorial contains a lot of interactive, editable examples and many exercises to check the student's progress.In the assessment tool various electronic evaluators check for the conformance of uploaded student programs to coding conventions, proper documentation, compliance with the specification and, last but not least, the correct execution of supplied functional tests.The tool not only provides a tremendous help for the correctors by reducing the manual assessment time by a factor of about 4, but also is appreciated by the students for its immediate reaction, because development times (especially during debugging) can be shortened considerably and students can gain a much higher confidence in the quality of their own program.

Improving the quality of programming education by online assessment

Simplifying Source Code Analysis by an XML Representation.

https://pi.informatik.uni-siegen.de/stt/23_2/01_Fachgruppenberichte/wsr2003.pdf

Gregor Fischer

Papers

Clone detection in source code by frequent itemset techniques

Abstract Syntax Trees - and their Role in Model Driven Software Development

Improving the quality of programming education by online assessment

Simplifying Source Code Analysis by an XML Representation.

Reasoning about Source Code in XML-Representation.