A Non-Deterministic Approach to Restructuring Flow Graphs

The history of programming is filled with works about the properties of program flow graphs. There are many approaches to defining the quality of such graphs, and to improving a given flow graph by restructuring the underlying source code. We present here a new, twofold approach to restructuring the control flow of arbitrary source code. The first part of the method is a classical deterministic algorithm; the second part is non-deterministic and involves user interaction. The method is based on node splitting, enabling it to satisfy the definition of the extended Nassi-Shneiderman diagrams

Knowledge restructing and the development of expertise in computer programming

This thesis reports a number of empirical studies exploring the development of expertise in computer programming. Experiments 1 and 2 are concerned with the way in which the possession of design experience can influence the perception and use of cues to various program structures. Experiment 3 examines how violations to standard conventions for constructing programs can affect the comprehension of expert, intermediate and novice subjects. Experiment 4 looks at the differences in strategy that are exhibited by subjects of varying skill level when constructing programs in different languages. Experiment 5 takes these ideas further to examine the temporal distribution of different forms of strategy during a program generation task. Experiment 6 provides evidence for salient cognitive structures derived from reaction time and error data in the context of a recognition task. Experiments 7 and 8 are concerned with the role of working memory in program generation and suggest that one aspect of expertise in the programming domain involves the acquisition of strategies for utilising display-based information. The final chapter attempts to bring these experimental findings together in terms of a model of knowledge organisation that stresses the importance of knowledge restructuring processes in the development of expertise. This is contrasted with existing models which have tended to place emphasis upon schemata acquisition and generalisation as the fundamental modes of learning associated with skill development. The work reported here suggests that a fine-grained restructuring of individual schemata takes places during the later stages of skill development. It is argued that those mechanisms currently thought to be associated with the development of expertise may not fully account for the strategic changes and the types of error typically found in the transition between novice, intermediate and expert problem solvers. This work has a number of implications for existing theories of skill acquisition. In particular, it questions the ability of such theories to account for subtle changes in the various manifestations of skilled performance that are associated with increasing expertise. Secondly, the work reported in this thesis attempts to show how specific forms of training might give rise to the knowledge restructuring process that is proposed. Finally, the thesis stresses the important role of display-based problem solving in complex tasks such as programming and highlights the role of programming language notation as a mediating factor in the development and acquisition of problem solving strategies

Code Generation in the Columbia Esterel Compiler

The synchronous language Esterel provides deterministic concurrency by adopting a semantics in which threads march in step with a global clock and communicate in a very disciplined way. Its expressive power comes at a cost, however: it is a difficult language to compile into machine code for standard von Neumann processors. The open-source Columbia Esterel Compiler is a research vehicle for experimenting with new code generation techniques for the language. Providing a front-end and a fairly generic concurrent intermediate representation, a variety of back-ends have been developed. We present three of the most mature ones, which are based on program dependence graphs, dynamic lists, and a virtual machine. After describing the very different algorithms used in each of these techniques, we present experimental results that compares twenty-four benchmarks generated by eight different compilation techniques running on seven different processors

Code Generation in the Columbia Esterel Compiler

The synchronous language Esterel provides deterministic concurrency by adopting a semantics in which threads march in step with a global clock and communicate in a very disciplined way. Its expressive power comes at a cost, however: it is a difficult language to compile into machine code for standard von Neumann processors. The open-source Columbia Esterel Compiler is a research vehicle for experimenting with new code generation techniques for the language. Providing a front-end and a fairly generic concurrent intermediate representation, a variety of back-ends have been developed. We present three of the most mature ones, which are based on program dependence graphs, dynamic lists, and a virtual machine. After describing the very different algorithms used in each of these techniques, we present experimental results that compares twenty-four benchmarks generated by eight different compilation techniques running on seven different processors

Fortran refactoring for legacy systems

The motivation of this work comes from a Global Climate Model (GCM) Software which was in great need of being updated. This software was implemented by scientists in the ’80s as a result of meteorological research. Written in Fortran 77, this program has been used as an input to make climate predictions for the Southern Hemisphere. The execution to get a complete numerical data set takes several days. This software has been programmed using a sequential processing paradigm. In these days, where multicore processors are so widespread, the time that an execution takes to get a complete useful data set can be drastically reduced using this technology. As a first objective to reach this goal of reengineering we must be able to understand the source code. An essential Fortran code characteristic is that old source code versions became unreadable, not comprehensive and sometimes “ejects” the reader from the source code. In that way, we can not modify, update or improve unreadable source code. Then, as a first step to parallelize this code we must update it, turn it readable and easy to understand. The GCM has a very complex internal structure. The program is divided into about 300 .f (Fortran 77) files. These files generally implement only one Fortran subroutine. Less than 10% of the files are used for common blocks and constants. Approximately 25% of the lines in the source code are comments. The total number of Fortran source code lines is 58000. A detailed work within the source code brings to light that [74]: 1 About 230 routines are called/used at run time. Most of the runtime is spent in routines located at deep levels 5 to 7 in the dynamic call graph from the main routine. 2 The routine with most of the runtime (the top routine from now on) requires more than 9% of the total program runtime and is called about 315000 times. 3 The top 10 routines (the 10 routines at the top of the flat profile) require about 50% of total runtime. Two of them are related to intrinsic Fortran functions. Our first approach was using a scripting language and Find & Replace tools trying to upgrade the source code, this kind of code manipulation do not guarantee preservation of software behavior. Then, our goal was to develop an automated tool to transform legacy software in more understandable, comprehensible and readable applying refactoring as main technique. At the same time a catalog of transformation to be applied in Fortran code is needed as a guide to programmers through this process.Es revisado por: http://sedici.unlp.edu.ar/handle/10915/9703Facultad de Informátic

Agile model-driven re-engineering

In this paper we describe an Agile model-driven engineering (MDE) approach, AMDRE, for the re-engineering of legacy systems. The objective is to support the reuse of business-critical functionality from such systems and the porting of legacy code to modernised platforms, together with technical debt reduction to improve the system maintainability and extend its useful life. AMDRE uses a lightweight MDE process which involves the automated abstraction of software systems to UML specifications and the interactive application of refactoring and rearchitecting transformations to remove quality flaws and architectural flaws. We demonstrate the approach on Visual Basic, COBOL and Python legacy codes, including a finance industry case. Significant quality improvements are achieved, and translation accuracy over 80\% is demonstrated. In comparison to other MDE re-engineering approaches, AMDRE does not require high MDE skills and should be usable by mainstream software practitioners

XPDec: an XML plagiarism detection system for procedural programming languages

Plagiarisms are frequently occurring in the Computer Science courses, especially in computer programming. In this thesis, XML plagiarism detection model is introduced and XML is used as an intermediate data exchange mechanism in the suggested model. Since a procedural programming language is defined by its specific rules and it is well-structured form, we can generate an XML document from a program source based on the XML schema. As long as we can generate XML documents from given program sources, XML queries to extract information how they are similar to each other can be queried over the documents. This idea makes us encourage to moving our attention to plagiarism detection models. As the result of this study, XML Plagiarism Detection System (XPDec) has been developed. The plagiarism detection systems for programming can be classified into two main groups: attribute-counting based systems and structural metrics based systems. XPDec system uses the combined detection mechanism. In addition to the mechanism, XPDec system is adopting the XML query language suggested in XML plagiarism detection model to extract control sequences from XML documents. This mechanism increases the accuracy of the results. At the end of this thesis we shows that the XPDec system gives high accuracy results to finding similarities among the given source programs

CLIPS template system for program understanding

Program understanding is a subfield of software reengineering and attempts to recognize the run-time behavior of source code. To this point, success in this area has been limited to very small code segments. An expert system, HLAR (High-Level Algorithm Recognizer), has been written in CLIPS and recognizes three sorting algorithms, selection sort, quicksort, and heapsort. This paper describes the HLAR system in general and, in depth, the CLIPS templates used for program representation and understanding