Applying Model-Driven Engineering to Development Scenarios for Web Content Management System Extensions

Web content management systems (WCMSs) such as WordPress, Joomla or Drupal have established themselves as popular platforms for instantiating dynamic web applications. Using a WCMS instance allows developers to add additional functionality by implementing installable extension packages. However, extension developers are challenged by dealing with boilerplate code, dependencies between extensions and frequent architectural changes to the underlying WCMS platform. These challenges occur in frequent development scenarios that include initial development and maintenance of extensions as well as migration of existing extension code to new platforms. A promising approach to overcome these challenges is represented by model-driven engineering (MDE). Adopting MDE as development practice, allows developers to define software features within reusable models which abstract the technical knowledge of the targeted system. Using these models as input for platform-specific code generators enables a rapid transformation to standardized software of high quality. However, MDE has not found adoption during extension development in the WCMS domain, due to missing tool support. The results of empirical studies in different domains demonstrate the benefits of MDE. However, empirical evidence of these benefits in the WCMS domain is currently lacking. In this work, we present the concepts and design of an MDE infrastructure for the development and maintenance of WCMS extensions. This infrastructure provides a domain-specific modelling language (DSL) for WCMS extensions, as well as corresponding model editors. In addition, the MDE infrastructure facilitates a set of transformation tools to apply forward and reverse engineering steps. This includes a code generator that uses model instances of the introduced DSL, an extension extractor for code extraction of already deployed WCMS extensions, and a model extraction tool for the creation of model instances based on an existing extension package. To ensure adequacy of the provided MDE infrastructure, we follow a structured research methodology. First, we investigate the representativeness of common development scenarios by conducting interviews with industrial practitioners from the WCMS domain. Second, we propose a general solution concept for these scenarios including involved roles, process steps, and MDE infrastructure facilities. Third, we specify functional and non-functional requirements for an adequate MDE infrastructure, including the expectations of domain experts. To show the applicability of these concepts, we introduce JooMDD as infrastructure instantiation for the Joomla WCMS which provides the most sophisticated extension mechanism in the domain. To gather empirical evidence of the positive impact of MDE during WCMS extension development, we present a mixed-methods empirical investigation with extension developers from the Joomla community. First, we share the method, results and conclusions of a controlled experiment conducted with extension developers from academia and industry. The experiment compares conventional extension development with MDE using the JooMDD infrastructure, focusing on the development of dependent and independent extensions. The results show a clear gain in productivity and quality by using the JooMDD infrastructure. Second, we share the design and observations of a semi-controlled tutorial with four experienced developers who had to apply the JooMDD infrastructure during three scenarios of developing new (both independent and dependent) extensions and of migrating existing ones to a new major platform version. The aim of this study was to obtain direct qualitative feedback about acceptance, usefulness, and open challenges of our MDE approach. Finally, we share lessons learned and discuss the threats to validity of the conducted studies

Parameterized Rural Postman Problem

The Directed Rural Postman Problem (DRPP) can be formulated as follows: given a strongly connected directed multigraph $D=(V,A)$ with nonnegative integral weights on the arcs, a subset $R$ of $A$ and a nonnegative integer $\ell$, decide whether $D$ has a closed directed walk containing every arc of $R$ and of total weight at most $\ell$. Let $k$ be the number of weakly connected components in the the subgraph of $D$ induced by $R$. Sorge et al. (2012) ask whether the DRPP is fixed-parameter tractable (FPT) when parameterized by $k$, i.e., whether there is an algorithm of running time $O^*(f(k))$ where $f$ is a function of $k$ only and the $O^*$ notation suppresses polynomial factors. Sorge et al. (2012) note that this question is of significant practical relevance and has been open for more than thirty years. Using an algebraic approach, we prove that DRPP has a randomized algorithm of running time $O^*(2^k)$ when $\ell$ is bounded by a polynomial in the number of vertices in $D$. We also show that the same result holds for the undirected version of DRPP, where $D$ is a connected undirected multigraph

Invertible Program Restructurings for Continuing Modular Maintenance

When one chooses a main axis of structural decompostion for a software, such as function- or data-oriented decompositions, the other axes become secondary, which can be harmful when one of these secondary axes becomes of main importance. This is called the tyranny of the dominant decomposition. In the context of modular extension, this problem is known as the Expression Problem and has found many solutions, but few solutions have been proposed in a larger context of modular maintenance. We solve the tyranny of the dominant decomposition in maintenance with invertible program transformations. We illustrate this on the typical Expression Problem example. We also report our experiments with Java and Haskell programs and discuss the open problems with our approach.Comment: 6 pages, Early Research Achievements Track; 16th European Conference on Software Maintenance and Reengineering (CSMR 2012), Szeged : Hungary (2012

Reversible Computation in Term Rewriting

Essentially, in a reversible programming language, for each forward computation from state $S$ to state $S'$, there exists a constructive method to go backwards from state $S'$ to state $S$. Besides its theoretical interest, reversible computation is a fundamental concept which is relevant in many different areas like cellular automata, bidirectional program transformation, or quantum computing, to name a few. In this work, we focus on term rewriting, a computation model that underlies most rule-based programming languages. In general, term rewriting is not reversible, even for injective functions; namely, given a rewrite step $t_1 \rightarrow t_2$, we do not always have a decidable method to get $t_1$ from $t_2$. Here, we introduce a conservative extension of term rewriting that becomes reversible. Furthermore, we also define two transformations, injectivization and inversion, to make a rewrite system reversible using standard term rewriting. We illustrate the usefulness of our transformations in the context of bidirectional program transformation.Comment: To appear in the Journal of Logical and Algebraic Methods in Programmin

From Event-B models to Dafny code contracts

International audienceThe constructive approach to software correctness aims at formal modelling and verification of the structure and behaviour of a system in different levels of abstraction. In contrast, the analytical approach to software verification focuses on code level correctness and its verification. Therefore it would seem that the constructive and analytical approaches should complement each other well. To demonstrate this idea we present a case for linking two existing verification methods, Event-B (constructive) and Dafny (analytical). This approach combines the power of Event-B abstraction and its stepwise refinement with the verification capabilities of Dafny. We presented a small case study to demonstrate this approach and outline of the rules for transforming Event-B events to Dafny contracts. Finally, a tool for automatic generation of Dafny contracts from Event-B formal models is presented

Linear transformation distance for bichromatic matchings

Let $P=B\cup R$ be a set of $2n$ points in general position, where $B$ is a set of $n$ blue points and $R$ a set of $n$ red points. A \emph{$BR$-matching} is a plane geometric perfect matching on $P$ such that each edge has one red endpoint and one blue endpoint. Two $BR$-matchings are compatible if their union is also plane. The \emph{transformation graph of $BR$-matchings} contains one node for each $BR$-matching and an edge joining two such nodes if and only if the corresponding two $BR$-matchings are compatible. In SoCG 2013 it has been shown by Aloupis, Barba, Langerman, and Souvaine that this transformation graph is always connected, but its diameter remained an open question. In this paper we provide an alternative proof for the connectivity of the transformation graph and prove an upper bound of $2n$ for its diameter, which is asymptotically tight

Some issues in the 'archaeology' of software evolution

During a software project's lifetime, the software goes through many changes, as components are added, removed and modified to fix bugs and add new features. This paper is intended as a lightweight introduction to some of the issues arising from an `archaeological' investigation of software evolution. We use our own work to look at some of the challenges faced, techniques used, findings obtained, and lessons learnt when measuring and visualising the historical changes that happen during the evolution of software