Attribution Required: Stack Overflow Code Snippets in GitHub Projects

Stack Overflow (SO) is the largest Q&A website for developers, providing a huge amount of copyable code snippets. Using these snippets raises various maintenance and legal issues. The SO license requires attribution, i.e., referencing the original question or answer, and requires derived work to adopt a compatible license. While there is a heated debate on SO's license model for code snippets and the required attribution, little is known about the extent to which snippets are copied from SO without proper attribution. In this paper, we present the research design and summarized results of an empirical study analyzing attributed and unattributed usages of SO code snippets in GitHub projects. On average, 3.22% of all analyzed repositories and 7.33% of the popular ones contained a reference to SO. Further, we found that developers rather refer to the whole thread on SO than to a specific answer. For Java, at least two thirds of the copied snippets were not attributed.Comment: 3 pages, 1 figure, Proceedings of the 39th International Conference on Software Engineering Companion (ICSE-C 2017), IEEE, 2017, pp. 161-16

Semantics-directed generation of compilers and abstract machines

In traditional compiler design the work of a compiler is divided into several phases: lexical, syntactical and semantical analysis, optimizations and code generation. For several of these phases generators exist -- most prominently LEX and YACC for generating lexical and syntactical analyzers. A common feature of all generators is that the phase in the compiler is described using a meta-language (e.g. regular expressions or context-free grammars) and that the generator produces the related compiler module. There exist several good textbooks on compiler design. However, all of these books present ready made mappings from source language constructs to target language constructs, the so called translation schemes, instead of deriving them. Hence, the reader is expected to learn how to design code generators by analysing translation schemes as opposed to from first principles. The same is true for abstract machines. Abstract machines are virtual target architectures which support the concepts of the source language. Typically abstract machines are presented together with translation schemes from the source language to the abstract machine language. There is only little work on how translation schemes and abstract machines are designed. The aim of our work is to detect underlying principles that relate abstract machines to programming language semantics, and to automate part of the design process for abstract machines. Thus, we need to ensure that the behaviour of a source program will be maintained by translating it into the abstract machine language, and then applying the abstract machine. The behaviour of a program will depend on it\u27s semantics. Often this aspect of a programming language is only described in natural language which is both ambiguous and vague. We shall use formal techniques to describe the meaning of programs in a particular language and to prove that our transformations are correct. In this thesis we concentrate on natural semantics, but we also address action semantics

Semantics-directed generation of compilers and abstract machines

In traditional compiler design the work of a compiler is divided into several phases: lexical, syntactical and semantical analysis, optimizations and code generation. For several of these phases generators exist -- most prominently LEX and YACC for generating lexical and syntactical analyzers. A common feature of all generators is that the phase in the compiler is described using a meta-language (e.g. regular expressions or context-free grammars) and that the generator produces the related compiler module. There exist several good textbooks on compiler design. However, all of these books present ready made mappings from source language constructs to target language constructs, the so called translation schemes, instead of deriving them. Hence, the reader is expected to learn how to design code generators by analysing translation schemes as opposed to from first principles. The same is true for abstract machines. Abstract machines are virtual target architectures which support the concepts of the source language. Typically abstract machines are presented together with translation schemes from the source language to the abstract machine language. There is only little work on how translation schemes and abstract machines are designed. The aim of our work is to detect underlying principles that relate abstract machines to programming language semantics, and to automate part of the design process for abstract machines. Thus, we need to ensure that the behaviour of a source program will be maintained by translating it into the abstract machine language, and then applying the abstract machine. The behaviour of a program will depend on it's semantics. Often this aspect of a programming language is only described in natural language which is both ambiguous and vague. We shall use formal techniques to describe the meaning of programs in a particular language and to prove that our transformations are correct. In this thesis we concentrate on natural semantics, but we also address action semantics

On the congruence of modularity and code coupling

ABSTRACT Software systems are modularized to make their inherent complexity manageable. While there exists a set of wellknown principles that may guide software engineers to design the modules of a software system, we do not know which principles are followed in practice. In a study based on 16 open source projects, we look at different kinds of coupling concepts between source code entities, including structural dependencies, fan-out similarity, evolutionary coupling, code ownership, code clones, and semantic similarity. The congruence between these coupling concepts and the modularization of the system hints at the modularity principles used in practice. Furthermore, the results provide insights on how to support developers to modularize software systems