Object Variables and Flow Dependence Quiz

Program slicing is a technique to extract the part of the program that can affect the values computed at a given program point, known as the slicing criterion. It is significant in Java programs to understand and analyze the impact of specific code segments on the overall computation.

The System Dependence Graph (SDG) and its extensions like JSysDG and SSLDG are used to represent and analyze Java programs. These graphs help in understanding the dependencies and flow of values within the program, particularly in object-oriented Java programs.

The paper presents an incompleteness result showing that the System Dependence Graphs (SDGs), including JSysDG and SSLDG, do not always produce complete slices, especially when object variables are selected as the slicing criteria. This result highlights the limitations of these graph-based slicing techniques in certain cases.

Flow dependence and object-flow dependence are important concepts in program slicing of Java programs. They help in understanding the flow of data and dependencies between different parts of the program, particularly in the context of object-oriented programming. These dependencies play a crucial role in determining the impact of specific code segments on the overall computation.

The PDG is constructed from the CFG and contains control and flow dependences.

Control dependence occurs when a node post-dominates one but not all of another node's CFG successors.

Flow dependence occurs when a variable is defined at one node and used at another, without being redefined along the control-flow path between them.

The SDG connects the PDGs of all methods in a program, simulating parameter passing and method calls.

The SDG represents method parameters with formal-in and formal-out nodes, and method calls with actual-in and actual-out nodes.

Interprocedural parameter passing is represented with input and output arcs in the SDG.

The ClDG extends the SDG to consider object-oriented programs, representing class membership, data membership, and inheritance.

The JSysDG further extends the ClDG to handle polymorphic calls and dynamic binding in Java programs.

The JSysDG represents polymorphic method calls with a tree structure, with a node for each possible dynamic type connected to the corresponding method definition.

The JSysDG employs a k-limiting approach, where the tree representation is unfolded to a level k.

The JSysDG provides a graphical representation for scenarios involving polymorphic objects and method calls in Java programs.

JSysDG is a representation of Java object-oriented programs. It is considered the most accurate representation because it captures the dependencies between program statements and predicates that might affect the value of program variables.

JSysDG can produce incomplete slices, leading to limitations in its representation. In certain scenarios, the slice obtained by JSysDG is not complete when selecting some object variables as the slicing criterion.

In Java, program variables can be primitive or object variables.

Primitive variables are atomic and always defined and used atomically.

Object variables are compositionally formed by a collection of data members.

JSysDG was proposed by Walkinshaw et al. It extends the representation provided by Liang and Harrold for C++ by capturing the dependencies between program statements and predicates that might affect the value of program variables in Java.

Program slice and slicing criterion are defined as a set of program statements and predicates that might affect the value of a program variable.

Object variables can be considered as the slicing criterion, and the slice should include all statements that might affect the value of its data members.

Flow dependences between object definitions and uses in method calls are propagated through their data members, but they never connect the node that represents the object variable itself.

The standard notion of flow dependence for objects needs to be extended to solve the identified problem in JSysDG.

Object variables can be totally defined in a program statement if the execution of the statement makes the variable point to a different object, leading to split definitions of all the data members of the object variable.

The representation provided by Liang and Harrold for C++ was proposed by Liang and Harrold themselves.

Program representation is crucial for program analysis and transformation techniques because it provides a structured way to understand and manipulate the program's elements, such as objects and their dependencies, which is essential for tasks like software maintenance, debugging, and program specialization.

The paper proposes a program slicing technique for object-oriented programs based on a new program representation.

Program slicing is commonly used in software maintenance, debugging, and program specialization.

The proposed program representation aims to address the ill-defined representation of dependences between partial definitions of objects in existing approaches.

The extension of the representation with object-flow dependence allows for more accurate flow representation between object variables and their data members.

The new representation enables the obtainment of complete slices when an object variable is selected as the slicing criterion.

The proposed technique is illustrated using a Java code snippet and its corresponding slice with respect to a specific variable.

The Java System Dependence Graph (JSysDG) is a widely used program representation for slicing object-oriented programs.

The paper identifies a fundamental problem with JSysDG: it can produce incomplete slices in some scenarios.

The incompleteness problem arises from JSysDG's inability to select an object variable as the slicing criterion and include all its required data members in the slice.

The incompleteness of slices can lead to issues such as the slice not containing the bug or producing specialized code that is not equivalent to the original program.

The source of the problem is the ill-defined flow dependence in JSysDG, which leads to a lack of completeness in the slices.

The JSysDG and SSLDG fail to include all relevant data members and definitions in the resulting slice, leading to incomplete results when handling object variables in method calls.

The paper proposes introducing three more accurate definitions: standard flow dependence for primitive variables, object-flow dependence, and object-reference dependence to address the incompleteness issue.

The proposed approach requires the specialization of the 'defined variables' and 'used variables' sets of each statement in the JSysDG.

The paper is structured to recall key concepts about the construction of the JSysDG, explain and justify the incompleteness problem, redefine DEF and USE sets for every statement, introduce object-flow dependence and object-reference dependence, present slicing restrictions, provide empirical evaluation, review related work, and conclude.

The CFG represents all possible execution paths of a method, with each statement represented as a node connected if they may be executed sequentially.

Each CFG node is augmented with a definition set and a use set, denoting the variables defined and used at that node.

Definition 2.1 describes the definition set (DEF) as containing all program variables defined at a statement.

Definition 2.2 describes the use set (USE) as containing all program variables used at a statement.

The background information is aimed at providing a self-contained understanding of the JSysDG for readers.

To translate pseudo-code program into a programming language

To obtain complete slices in program slicing technique for object-oriented programs

As slicing criteria in JSysDG