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Machine Learning for Software Maintainability

The document discusses the application of machine learning techniques in software maintenance, emphasizing the importance of understanding software artifacts and reducing maintenance costs. It outlines various machine learning approaches for analyzing source code and detecting code clones, particularly through the use of kernel methods that facilitate the classification and clustering of software components. The case study on code clones highlights the use of abstract syntax trees and program dependency graphs to identify duplicated code fragments, thus improving software maintainability.

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MACHINE LEARNING FOR SOFTWARE MAINTAINABILITY Anna Corazza, Sergio Di Martino, Valerio Maggio Alessandro Moschitti, Andrea Passerini, Giuseppe Scanniello, Fabrizio Silverstri JIMSE 2012 August 28, 2012 Montpellier, France
SOFTWARE MAINTENANCE “A software system must be continuously adapted during its overall life cycle or it progressively becomes less satisfactory” (cit. Lehman’s Law of Software Evolution) • Software Maintenance is one of the most expensive and time consuming phase of the whole life cycle • Anticipating the Maintenance operations reduces the cost • 85%-90% of the total cost are related to the effort necessary to comprehend the system and its source code [Erlikh, 2000]
Software Artifacts UI Process Components UI Components Data Access Components Data Helpers / Utilities Security Operational Management Communications Business Components Application Facade Buisiness Workflows Messages Interfaces Service Interfaces • Provide models and views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE
• Provide models and views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE External Systems Service Consumers Services Service Interfaces Messages Interfaces Cross Cutting Security OperationalManagement Communications Data Data Access Components Data Helpers / Utilities Presentation UI Components UI Process Components Business Application Facade Buisiness Workflows Business Components Clusters of Software Artifacts
• Provide models and views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE External Systems Service Consumers Services Service Interfaces Messages Interfaces Cross Cutting Security OperationalManagement Communications Data Data Access Components Data Helpers / Utilities Presentation UI Components UI Process Components Business Application Facade Buisiness Workflows Business Components Clusters of Software Artifacts
Software Artifacts may be analyzed at different levels of abstractions SOFTWARE ARTIFACTS
Software Artifacts may be analyzed at different levels of abstractions SOFTWARE ARTIFACTS
Software Artifacts may be analyzed at different levels of abstractions The different levels of abstractions lead to different analysis tasks: • Identification of functional modules and their hierarchical arrangement • i.e., Clustering of Software classes • Identification of Code Clones • i.e., Clustering of Duplicated code fragments (blocks, SOFTWARE ARTIFACTS
• Mine information directly from the source code: • Exploit the syntactic/lexical information provided in the source code text • Exploit the relational information between artifacts • e.g., Program Dependencies Problem: Definition of a proper similarity measure to apply in the clustering analysis, which is able to exploit the considered representation of software artifacts SOFTWARE ARTIFACTS CLUSTERING
• Analysis of large and complex systems • Solutions and algorithms must be able to scale efficiently (in the large and in the many) MINING LARGE REPOSITORIES
Idea: Definition of Machine Learning techniques to mine information from the source code • Combine different kind of information (lexical and structural) • Application of Kernel Methods to software artifacts • Provide flexible and computational effective solutions to analyze large data sets ADVANCED MACHINE LEARNING FOR SOFTWARE MAINTENANCE
Idea: Definition of Machine Learning techniques to mine information from the source code • Combine different kind of information (lexical and structural) • Application of Kernel Methods to software artifacts • Provide flexible and computational effective solutions to analyze large data sets Advanced Machine Learning • Learning with syntactic/semantic information (Natural Language Processing) • Learning in relational domains (Structured-output learning, Logic Learning, Statistical Relational Learning) ADVANCED MACHINE LEARNING FOR SOFTWARE MAINTENANCE
KERNEL METHODS FOR STRUCTURED DATA • A Kernel is a function between (arbitrary) pairs of entities • It can be seen as a kind of similarity measure • Based on the idea that structured objects can be described in terms of their constituent parts • Generalize the computation of the dot product to arbitrary domains • Can be easily tailored to specific domains • Tree Kernels • Graph Kernels • ....
KERNELS FOR STRUCTURES            Computation of the dot product between (Graph) Structures
• Parse Trees represent the syntactic structure of a sentence • Tree Kernels can be used to measure the similarity between parse trees KERNELS FOR LANGUAGES
• Parse Trees represent the syntactic structure of a sentence • Tree Kernels can be used to measure the similarity between parse trees KERNELS FOR LANGUAGES • Abstract Syntax Trees (AST) represent the syntactic structure of a piece of code • Research on Tree Kernels for NLP carries over to AST (with adjustments) KERNELS FOR SOURCE CODE
KERNELS FOR PARSE TREE                                     
KERNELS FOR AST                                                                             
• Supervised Learning • Binary Classification • Multi-class Classification • Ranking • Unsupervised Learning • Clustering • Anomaly Detection Idea: Any learning algorithm relying on similarity measure can be used KERNEL MACHINES
KERNEL MACHINES FOR CONE DETECTION • Supervised Learning • Pairwise classifier: predict if a pair of fragments is clone • Unsupervised Learning • Clustering: cluster together all candidate clones
KERNEL FOR CLONES                                                                             
KERNEL LEARNING • Construct a number of candidate kernels with different characteristics • e.g., Ignore variables names or not • Employ kernel learning approaches which learn a weighted combination of candidate kernels • Useless/harmful kernels will get zero weight and will be discarded in the final model LEARNING SIMILARITIES
Supervised Clustering • Exploit information on already annotated pieces of software • Training examples are software projects/portions with annotation on existing clones (clustering) • A learning model uses training examples to refine the similarity measure for correctly clustering novel examples STRUCTURED-OUTPUT LEARNING
• Software has a rich structure and heterogeneous information • Advanced Machine learning approaches are promising for exploiting such information • Kernel Methods are natural candidate • e.g., see the analogy between NLP parse trees and AST • Many applications: • architecture recovery, code clone detection, vulnerability detection .... SUMMARY
CASE STUDY: KERNELS FOR CLONES
• Goal: “Identify and group all duplicated code fragments/functions” • Copy&Paste programming • Taxonomy of 4 different types of clones • Program Text similarities and Functional similarities • Clones affect the reliability and the maintainability of a software system CODE CLONE DETECTION
• Abstract Syntax Tree (AST) • Tree structure representing the syntactic structure of the different instructions of a program (function) • Program Dependencies Graph (PDG) • (Directed) Graph structure representing the relationship among the different statement of a program KERNELS FOR CLONESCODE STRUCTURES Kernels for Structured Data: • The source code could be represented by many different data structures
ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body = whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body = whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body = whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body = whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodes correspond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodes correspond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodes correspond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodes correspond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodes correspond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
CODE STRUCTURES PDG • Two Types of Nodes • Control Nodes (Dashed ones) • e.g., if - for - while - function calls... • Data Nodes • e.g., expressions - parameters... NODES AND EDGES while call-site argexpr
CODE STRUCTURES PDG • Two Types of Nodes • Control Nodes (Dashed ones) • e.g., if - for - while - function calls... • Data Nodes • e.g., expressions - parameters... • Two Types of Edges (i.e., dependencies) • Control edges (Dashed ones) • Data edges NODES AND EDGES while call-site argexpr
DEFINING KERNELS FOR STRUCTURED DATA • The definition of a new Kernel for a Structured Object requires the definition of: • Set of features to annotate each part of the object • A Kernel function to measure the similarity on the smallest part of the object • e.g., Nodes of AST and Graphs • A Kernel function to apply the computation on the different (sub)parts of the structured object KERNELS FOR CODE STRUCTURES
• Features: each node is characterized by a set of 4 features • Instruction Class • i.e., LOOP, CONDITIONAL_STATEMENT, CALL • Instruction • i.e., FOR, IF, WHILE, RETURN • Context • i.e., Instruction Class of the closer statement node • Lexemes • Lexical information gathered (recursively) from leaves KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST FOR FOR-INIT FOR- BODY
• Features: each node is characterized by a set of 4 features • Instruction Class • i.e., LOOP, CONDITIONAL_STATEMENT, CALL • Instruction • i.e., FOR, IF, WHILE, RETURN • Context • i.e., Instruction Class of the closer statement node • Lexemes • Lexical information gathered (recursively) from leaves KERNELS FOR CODE STRUCTURES: AST Instruction Class = LOOP Instruction = FOR Context = (e.g., LOOP) Lexemes = (e.g, name of variables in FOR- INIT..) TREE KERNELS FOR AST FOR FOR-INIT FOR- BODY
• Goal: Identify the maximum isomorphic Tree/Subtree • Comparison of blocks to each other • Blocks: Atomic unit for (sub) tree considered KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST BLOCK = = print x 1.0 y f x x y BLOCK = = print s 0.0 p f s 1.0 p
• Goal: Identify the maximum isomorphic Tree/Subtree • Comparison of blocks to each other • Blocks: Atomic unit for (sub) tree considered KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST BLOCK = = print x 1.0 y f x x y BLOCK = = print s 0.0 p f s 1.0 p
• Features of nodes: • Node Label • i.e., , WHILE, CALL-SITE, EXPR, ... • Node Type • i.e., Data Node or Control Node • Features of edges: • Edge Type • i.e., Data Edge or Control Edge KERNELS FOR CODE STRUCTURES: PDG GRAPH KERNELS FOR PDG while call-site arg expr expr
• Features of nodes: • Node Label • i.e., , WHILE, CALL-SITE, EXPR, ... • Node Type • i.e., Data Node or Control Node • Features of edges: • Edge Type • i.e., Data Edge or Control Edge KERNELS FOR CODE STRUCTURES: PDG Node Label = WHILE Node Type = Control Node GRAPH KERNELS FOR PDG while call-site arg expr expr Control Edge Data Edge
while call-site arg expr expr while call-site arg expr call-site GRAPH KERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
while call-site arg expr expr while call-site arg expr call-site GRAPH KERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
while call-site arg expr expr while call-site arg expr call-site GRAPH KERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
while call-site arg expr expr while call-site arg expr call-site GRAPH KERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: • To automatically modify an existing system with randomly generated clones EMPIRICAL EVALUATION
EVALUATION PROTOCOL • Comparison of results with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: • To automatically modify an existing system with randomly generated clones • Manual classification of candidate results EMPIRICAL EVALUATION
BENCHMARKS AND DATASET Project Size (KLOC) # PDGS Apache-2.2.14 343 3017 Python-2.5.1 435 5091 • Comparison with another Graph-based clone detector • MeCC (ICSE2011) • Baseline Dataset • Results provided by MeCC • Extended Dataset • Extension of Clones results by manual evaluation of candidate clones • Agreement rate calculation between the evaluators EMPIRICAL EVALUATION
EMPIRICAL EVALUATION OF TREE KERNEL FOR AST • Comparison with another (pure) AST-based clone detector • Clone Digger http://clonedigger.sourceforge.net/ • Comparison on a system with randomly seeded clones Results refer to clones where code fragments have been modified by adding/removing or changing code statements EVALUATION TREE KERNELS FOR AST
PRECISION, RECALL AND F1 PLOT 0 0.25 0.5 0.75 1 0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 Precision Recall F1 Clone results with different similarity thresholds EVALUATION TREE KERNELS FOR AST
LOREM I P S U M Threshold #Clones in the Baseline #Clones in the Extended Dataset 1.00 874 1089 0.99 874 1514 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.7" 0.8" 0.9" 0.99" 1" Soglia'di'Similarità' Apache'2.2.14'6'Precision'con'Oracolo'Esteso' Precision5 Baseline" Precision5 Extended" 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.99" 1" Soglia'di'Similarità' Apache'2.2.14'6'Recall'con'Oracolo'Esteso' Recall0 Baseline" Recall0 Extended" RESULTS WITH APACHE 2.2.14 EVALUATION GRAPH KERNELS FOR PDG
LOREM I P S U M Threshold #Clones in the Baseline #Clones in the Extended Dataset 1.00 858 1066 0.99 858 2119 0" 0.2" 0.4" 0.6" 0.8" 1" 1.2" 0.99" 1" Soglia'di'Similarità' Python'2.5.1'5'Precision'con'Oracolo' Esteso' Precision2 Baseline" Precision2 Extended" 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.7" 0.8" 0.9" 0.99" 1" Soglia'di'Similarità' Python'2.5.1'5'Recall'con'Oracolo'Esteso' Recall2Baseline" Recall2Extended" RESULTS WITH PYTHON 2.5.2 EVALUATION GRAPH KERNELS FOR PDG
CHALLENGES AND OPPORTUNITIES • Learning Kernel Functions from Data Set • Kernel Methods advantages: • flexible solution to be tailored to specific domain • efficient solution easy to parallelize • combinations of multiple kernels • Provide a publicly available data set
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Machine Learning for Software Maintainability

  • 1.
    MACHINE LEARNING FOR SOFTWARE MAINTAINABILITY Anna Corazza,Sergio Di Martino, Valerio Maggio Alessandro Moschitti, Andrea Passerini, Giuseppe Scanniello, Fabrizio Silverstri JIMSE 2012 August 28, 2012 Montpellier, France
  • 2.
    SOFTWARE MAINTENANCE “A softwaresystem must be continuously adapted during its overall life cycle or it progressively becomes less satisfactory” (cit. Lehman’s Law of Software Evolution) • Software Maintenance is one of the most expensive and time consuming phase of the whole life cycle • Anticipating the Maintenance operations reduces the cost • 85%-90% of the total cost are related to the effort necessary to comprehend the system and its source code [Erlikh, 2000]
  • 3.
    Software Artifacts UI Process Components UI Components DataAccess Components Data Helpers / Utilities Security Operational Management Communications Business Components Application Facade Buisiness Workflows Messages Interfaces Service Interfaces • Provide models and views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE
  • 4.
    • Provide modelsand views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE External Systems Service Consumers Services Service Interfaces Messages Interfaces Cross Cutting Security OperationalManagement Communications Data Data Access Components Data Helpers / Utilities Presentation UI Components UI Process Components Business Application Facade Buisiness Workflows Business Components Clusters of Software Artifacts
  • 5.
    • Provide modelsand views representing the relationships among different software artifacts • Clustering of Software Artifacts • Advantages: • To aid the comprehension • To reduce maintenance effort SOFTWARE ARCHITECTURE External Systems Service Consumers Services Service Interfaces Messages Interfaces Cross Cutting Security OperationalManagement Communications Data Data Access Components Data Helpers / Utilities Presentation UI Components UI Process Components Business Application Facade Buisiness Workflows Business Components Clusters of Software Artifacts
  • 6.
    Software Artifacts maybe analyzed at different levels of abstractions SOFTWARE ARTIFACTS
  • 7.
    Software Artifacts maybe analyzed at different levels of abstractions SOFTWARE ARTIFACTS
  • 8.
    Software Artifacts maybe analyzed at different levels of abstractions The different levels of abstractions lead to different analysis tasks: • Identification of functional modules and their hierarchical arrangement • i.e., Clustering of Software classes • Identification of Code Clones • i.e., Clustering of Duplicated code fragments (blocks, SOFTWARE ARTIFACTS
  • 9.
    • Mine informationdirectly from the source code: • Exploit the syntactic/lexical information provided in the source code text • Exploit the relational information between artifacts • e.g., Program Dependencies Problem: Definition of a proper similarity measure to apply in the clustering analysis, which is able to exploit the considered representation of software artifacts SOFTWARE ARTIFACTS CLUSTERING
  • 10.
    • Analysis oflarge and complex systems • Solutions and algorithms must be able to scale efficiently (in the large and in the many) MINING LARGE REPOSITORIES
  • 11.
    Idea: Definition ofMachine Learning techniques to mine information from the source code • Combine different kind of information (lexical and structural) • Application of Kernel Methods to software artifacts • Provide flexible and computational effective solutions to analyze large data sets ADVANCED MACHINE LEARNING FOR SOFTWARE MAINTENANCE
  • 12.
    Idea: Definition ofMachine Learning techniques to mine information from the source code • Combine different kind of information (lexical and structural) • Application of Kernel Methods to software artifacts • Provide flexible and computational effective solutions to analyze large data sets Advanced Machine Learning • Learning with syntactic/semantic information (Natural Language Processing) • Learning in relational domains (Structured-output learning, Logic Learning, Statistical Relational Learning) ADVANCED MACHINE LEARNING FOR SOFTWARE MAINTENANCE
  • 13.
    KERNEL METHODS FOR STRUCTUREDDATA • A Kernel is a function between (arbitrary) pairs of entities • It can be seen as a kind of similarity measure • Based on the idea that structured objects can be described in terms of their constituent parts • Generalize the computation of the dot product to arbitrary domains • Can be easily tailored to specific domains • Tree Kernels • Graph Kernels • ....
  • 14.
  • 15.
    • Parse Treesrepresent the syntactic structure of a sentence • Tree Kernels can be used to measure the similarity between parse trees KERNELS FOR LANGUAGES
  • 16.
    • Parse Treesrepresent the syntactic structure of a sentence • Tree Kernels can be used to measure the similarity between parse trees KERNELS FOR LANGUAGES • Abstract Syntax Trees (AST) represent the syntactic structure of a piece of code • Research on Tree Kernels for NLP carries over to AST (with adjustments) KERNELS FOR SOURCE CODE
  • 17.
    KERNELS FOR PARSE TREE                                    
  • 18.
    KERNELS FOR AST                                                                            
  • 19.
    • Supervised Learning •Binary Classification • Multi-class Classification • Ranking • Unsupervised Learning • Clustering • Anomaly Detection Idea: Any learning algorithm relying on similarity measure can be used KERNEL MACHINES
  • 20.
    KERNEL MACHINES FOR CONEDETECTION • Supervised Learning • Pairwise classifier: predict if a pair of fragments is clone • Unsupervised Learning • Clustering: cluster together all candidate clones
  • 21.
    KERNEL FOR CLONES                                                                            
  • 22.
    KERNEL LEARNING • Constructa number of candidate kernels with different characteristics • e.g., Ignore variables names or not • Employ kernel learning approaches which learn a weighted combination of candidate kernels • Useless/harmful kernels will get zero weight and will be discarded in the final model LEARNING SIMILARITIES
  • 23.
    Supervised Clustering • Exploitinformation on already annotated pieces of software • Training examples are software projects/portions with annotation on existing clones (clustering) • A learning model uses training examples to refine the similarity measure for correctly clustering novel examples STRUCTURED-OUTPUT LEARNING
  • 24.
    • Software hasa rich structure and heterogeneous information • Advanced Machine learning approaches are promising for exploiting such information • Kernel Methods are natural candidate • e.g., see the analogy between NLP parse trees and AST • Many applications: • architecture recovery, code clone detection, vulnerability detection .... SUMMARY
  • 25.
  • 26.
    • Goal: “Identifyand group all duplicated code fragments/functions” • Copy&Paste programming • Taxonomy of 4 different types of clones • Program Text similarities and Functional similarities • Clones affect the reliability and the maintainability of a software system CODE CLONE DETECTION
  • 27.
    • Abstract SyntaxTree (AST) • Tree structure representing the syntactic structure of the different instructions of a program (function) • Program Dependencies Graph (PDG) • (Directed) Graph structure representing the relationship among the different statement of a program KERNELS FOR CLONESCODE STRUCTURES Kernels for Structured Data: • The source code could be represented by many different data structures
  • 28.
    ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body =whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
  • 29.
    ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body =whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
  • 30.
    ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body =whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
  • 31.
    ABSTRACT SYNTAX TREE (AST) CODE STRUCTURES AST Function Body =whileprint k 10 = i + p = i 0 i 1.0 < i 7 AST embeds both Syntactic and Lexical Information • Program Instructions • Name of Variables, Literals...
  • 32.
    while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodescorrespond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
  • 33.
    while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodescorrespond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
  • 34.
    while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodescorrespond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
  • 35.
    while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodescorrespond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
  • 36.
    while call-site expr decl param expr decl arg expr CODE STRUCTURES PDG • Nodescorrespond to instructions • Edges represent relationships between couple of nodes PROGRAM DEPENDENCIES GRAPH (PDG)
  • 37.
    CODE STRUCTURES PDG • Two Typesof Nodes • Control Nodes (Dashed ones) • e.g., if - for - while - function calls... • Data Nodes • e.g., expressions - parameters... NODES AND EDGES while call-site argexpr
  • 38.
    CODE STRUCTURES PDG • Two Typesof Nodes • Control Nodes (Dashed ones) • e.g., if - for - while - function calls... • Data Nodes • e.g., expressions - parameters... • Two Types of Edges (i.e., dependencies) • Control edges (Dashed ones) • Data edges NODES AND EDGES while call-site argexpr
  • 39.
    DEFINING KERNELS FOR STRUCTUREDDATA • The definition of a new Kernel for a Structured Object requires the definition of: • Set of features to annotate each part of the object • A Kernel function to measure the similarity on the smallest part of the object • e.g., Nodes of AST and Graphs • A Kernel function to apply the computation on the different (sub)parts of the structured object KERNELS FOR CODE STRUCTURES
  • 40.
    • Features: eachnode is characterized by a set of 4 features • Instruction Class • i.e., LOOP, CONDITIONAL_STATEMENT, CALL • Instruction • i.e., FOR, IF, WHILE, RETURN • Context • i.e., Instruction Class of the closer statement node • Lexemes • Lexical information gathered (recursively) from leaves KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST FOR FOR-INIT FOR- BODY
  • 41.
    • Features: eachnode is characterized by a set of 4 features • Instruction Class • i.e., LOOP, CONDITIONAL_STATEMENT, CALL • Instruction • i.e., FOR, IF, WHILE, RETURN • Context • i.e., Instruction Class of the closer statement node • Lexemes • Lexical information gathered (recursively) from leaves KERNELS FOR CODE STRUCTURES: AST Instruction Class = LOOP Instruction = FOR Context = (e.g., LOOP) Lexemes = (e.g, name of variables in FOR- INIT..) TREE KERNELS FOR AST FOR FOR-INIT FOR- BODY
  • 42.
    • Goal: Identifythe maximum isomorphic Tree/Subtree • Comparison of blocks to each other • Blocks: Atomic unit for (sub) tree considered KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST BLOCK = = print x 1.0 y f x x y BLOCK = = print s 0.0 p f s 1.0 p
  • 43.
    • Goal: Identifythe maximum isomorphic Tree/Subtree • Comparison of blocks to each other • Blocks: Atomic unit for (sub) tree considered KERNELS FOR CODE STRUCTURES: AST TREE KERNELS FOR AST BLOCK = = print x 1.0 y f x x y BLOCK = = print s 0.0 p f s 1.0 p
  • 44.
    • Features ofnodes: • Node Label • i.e., , WHILE, CALL-SITE, EXPR, ... • Node Type • i.e., Data Node or Control Node • Features of edges: • Edge Type • i.e., Data Edge or Control Edge KERNELS FOR CODE STRUCTURES: PDG GRAPH KERNELS FOR PDG while call-site arg expr expr
  • 45.
    • Features ofnodes: • Node Label • i.e., , WHILE, CALL-SITE, EXPR, ... • Node Type • i.e., Data Node or Control Node • Features of edges: • Edge Type • i.e., Data Edge or Control Edge KERNELS FOR CODE STRUCTURES: PDG Node Label = WHILE Node Type = Control Node GRAPH KERNELS FOR PDG while call-site arg expr expr Control Edge Data Edge
  • 46.
    while call-site arg expr expr while call-site arg expr call-site GRAPHKERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
  • 47.
    while call-site arg expr expr while call-site arg expr call-site GRAPHKERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
  • 48.
    while call-site arg expr expr while call-site arg expr call-site GRAPHKERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
  • 49.
    while call-site arg expr expr while call-site arg expr call-site GRAPHKERNELS FOR PDG • Goal: Identify common subgraphs • Selectors: Compare nodes to each others and explore the subgraphs of only “compatible” nodes (i.e., Nodes of the same type) • Context: The subgraph of a node (with paths whose lengths are at most L to avoid loops) KERNELS FOR CODE STRUCTURES: PDG
  • 50.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector EMPIRICAL EVALUATION
  • 51.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset EMPIRICAL EVALUATION
  • 52.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems EMPIRICAL EVALUATION
  • 53.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available EMPIRICAL EVALUATION
  • 54.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: EMPIRICAL EVALUATION
  • 55.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: • To automatically modify an existing system with randomly generated clones EMPIRICAL EVALUATION
  • 56.
    EVALUATION PROTOCOL • Comparison ofresults with other two clone detector tools: • AST-based Clone detector • PDG-based Clone Detector • No publicly available clone detection dataset • No unique set of analyzed open source systems • Usually clone results are not available • Two possible strategies: • To automatically modify an existing system with randomly generated clones • Manual classification of candidate results EMPIRICAL EVALUATION
  • 57.
    BENCHMARKS AND DATASET Project Size(KLOC) # PDGS Apache-2.2.14 343 3017 Python-2.5.1 435 5091 • Comparison with another Graph-based clone detector • MeCC (ICSE2011) • Baseline Dataset • Results provided by MeCC • Extended Dataset • Extension of Clones results by manual evaluation of candidate clones • Agreement rate calculation between the evaluators EMPIRICAL EVALUATION
  • 58.
    EMPIRICAL EVALUATION OF TREEKERNEL FOR AST • Comparison with another (pure) AST-based clone detector • Clone Digger http://clonedigger.sourceforge.net/ • Comparison on a system with randomly seeded clones Results refer to clones where code fragments have been modified by adding/removing or changing code statements EVALUATION TREE KERNELS FOR AST
  • 59.
    PRECISION, RECALL ANDF1 PLOT 0 0.25 0.5 0.75 1 0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74 0.76 0.78 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 Precision Recall F1 Clone results with different similarity thresholds EVALUATION TREE KERNELS FOR AST
  • 60.
    LOREM I P SU M Threshold #Clones in the Baseline #Clones in the Extended Dataset 1.00 874 1089 0.99 874 1514 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.7" 0.8" 0.9" 0.99" 1" Soglia'di'Similarità' Apache'2.2.14'6'Precision'con'Oracolo'Esteso' Precision5 Baseline" Precision5 Extended" 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.99" 1" Soglia'di'Similarità' Apache'2.2.14'6'Recall'con'Oracolo'Esteso' Recall0 Baseline" Recall0 Extended" RESULTS WITH APACHE 2.2.14 EVALUATION GRAPH KERNELS FOR PDG
  • 61.
    LOREM I P SU M Threshold #Clones in the Baseline #Clones in the Extended Dataset 1.00 858 1066 0.99 858 2119 0" 0.2" 0.4" 0.6" 0.8" 1" 1.2" 0.99" 1" Soglia'di'Similarità' Python'2.5.1'5'Precision'con'Oracolo' Esteso' Precision2 Baseline" Precision2 Extended" 0" 0.1" 0.2" 0.3" 0.4" 0.5" 0.6" 0.7" 0.8" 0.9" 0.99" 1" Soglia'di'Similarità' Python'2.5.1'5'Recall'con'Oracolo'Esteso' Recall2Baseline" Recall2Extended" RESULTS WITH PYTHON 2.5.2 EVALUATION GRAPH KERNELS FOR PDG
  • 62.
    CHALLENGES AND OPPORTUNITIES • LearningKernel Functions from Data Set • Kernel Methods advantages: • flexible solution to be tailored to specific domain • efficient solution easy to parallelize • combinations of multiple kernels • Provide a publicly available data set
  • 63.
    THANK YOU FOR YOURKIND ATTENTION