Regina Hebig

Making control loops explicit when architecting self-adaptive systems

Many self-adaptive systems include control loops between the core system and specific control elements which realize the self-adaptation capabilities. This is also true albeit at a higher level of abstraction for decentralized architectures. However, the available techniques to describe the software architecture of such systems do not support to make the control loops explicit. Therefore, architecting self-adaptive systems and their self-adaptation logic is today not well supported. In this paper, we present a UML profile for control loops that extends UML modeling concepts such that control loops become first class elements of the architecture. This enables that the architecture reflects control loops as crucial elements of the software architecture of these systems. Furthermore, it supports to design control loops as well as the interplay of multiple control loops at the architectural level. In addition, warning signals and related analysis activities are presented that can be used to analyze whether a given architectural UML model using the profile includes potentially problematic occurrences of control loops.

The quest for open source projects that use UML: mining GitHub

Context: While industrial use of UML was studied intensely, little is known about UML use in Free/Open Source Software (FOSS) projects. Goal: We aim at systematically mining GitHub projects to answer the question when models, if used, are created and updated throughout the whole projects life-span. Method: We present a semi-automated approach to collect UML stored in images, .xmi, and .uml files and scanned ten percent of all GitHub projects (1.24 million). Our focus was on number and role of contributors that created/updated models and the time span during which this happened. Results: We identified and studied 21 316 UML diagrams within 3 295 projects. Conclusion: Creating/updating of UML happens most often during a very short phase at the project start. For 12% of the models duplicates were found, which are in average spread across 1.88 projects. Finally, we contribute a list of GitHub projects that include UML files.

A Web Service Architecture for Decentralised Identity- and Attribute-Based Access Control

The loosely coupled nature of Service-oriented Architectures raises the question how information for access control can be managed in an efficient way. Several specifications for Web Services exist to describe security requirements and to facilitate a provision of identity information. However, the integration of different standards regarding the expression of identity information in policies, claims and assertions comes along with an increased complexity. In order to identify and address the problems occurring with the combined use of standards as XACML, SAML and WS-Trust, we designed and implemented an architecture for identity- and attribute-based access control in decentralized environments. Our implementation provides an automated generation of access control policies in a format called XACML, a way to communicate required user attributes as claims across different domains based on the standards WS-Trust and WS-Policy, and a consistent mapping of retrieved attribute assertions to the XACML attributes in the access control policy.

On the need to study the impact of model driven engineering on software processes

There is an increasing use of model-driven engineering (MDE) in the industry. Despite the existence of research proposals for MDE-specific processes, the question arises whether and how the processes that are already used within a company can be reused, when MDE is introduced. In this position paper we report on a systematic literature review on the question how standard processes, such as SCRUM or the V-Model XT, can be combined with MDE. We come up with the observation that - although it is in some cases possible to reuse standard processes - the combination with MDE can also result in heavyweight changes to a process. Our goal is to draw attention to two arising research needs: the need to collect systematic knowledge about the influence of MDE on software processes and the need to provide guidance for the tailoring of processes based on the set of used MDE techniques.

Detecting complex changes and refactorings during (Meta)model evolution

Evolution of metamodels can be represented at the finest grain by the trace of atomic changes such as add, delete, and update of elements. For many applications, like automatic correction of models when the metamodel evolves, a higher grained trace must be inferred, composed of complex changes, each one aggregating several atomic changes. Complex change detection is a challenging task since multiple sequences of atomic changes may define a single user intention and complex changes may overlap over the atomic change trace.In this paper, we propose a detection engine of complex changes that simultaneously addresses these two challenges of variability and overlap. We introduce three ranking heuristics to help users to decide which overlapping complex changes are likely to be correct. In our approach, we record the trace of atomic changes rather than computing them with the difference between the original and evolved metamodel. Thus, we have a complete and an ordered sequence of atomic changes without hidden changes. Furthermore, we consider the issue of undo operations (i.e. change canceling actions) while recording the sequence of atomic changes, and we illustrate how we cope with it. We validate our approach on 8 real case studies demonstrating its feasibility and its applicability. We observe that a full recall is always reached in all case studies and an average precision of 70.75%. The precision is improved by the heuristics up to 91% and 100% in some cases. HighlightsRecording the trace of atomic changes ensure the chronological order and the absence of hidden changes.Both issues of hidden changes and overlapping complex changes reduce the recall of the detection, if not considered.Our detection algorithm reaches 100% recall for the eight case studies.In the eight case studies, our heuristics never rank the correct overlapping complex changes with a lower priority than the incorrect ones.

On the Complex Nature of MDE Evolution

In Model-Driven Engineering MDE the employed setting of languages as well as automated and manual activities has major impact on productivity. Furthermore, such settings for MDE evolve over time. However, currently only the evolution of modeling languages, tools, and transformations is studied in research. It is not clear whether these are the only relevant changes that characterize MDE evolution in practice. In this paper we address this lack of knowledge. We first discuss possible changes and then report on a first study that demonstrates that these forms of evolution can be commonly observed in practice. To investigate the complex nature of MDE evolution in more depth, we captured the evolution of three MDE settings from practice and derive eight observations concerning reasons for MDE evolution. Based on the observations we then identify open research challenge concerning MDE evolution.

Approaches to Co-Evolution of Metamodels and Models: A Survey

Modeling languages, just as all software artifacts, evolve. This poses the risk that legacy models of a company get lost, when they become incompatible with the new language version. To address this risk, a multitude of approaches for metamodel-model co-evolution were proposed in the last 10 years. However, the high number of solutions makes it difficult for practitioners to choose an appropriate approach. In this paper, we present a survey on 31 approaches to support metamodel-model co-evolution. We introduce a taxonomy of solution techniques and classify the existing approaches. To support researchers, we discuss the state of the art, in order to better identify open issues. Furthermore, we use the results to provide a decision support for practitioners, who aim to adopt solutions from research.

Metamodel and Constraints Co-evolution: A Semi Automatic Maintenance of OCL Constraints

Metamodels are core components of modeling languages to define structural aspects of a business domain. As a complement, OCL constraints are used to specify detailed aspects of the business domain, e.g. more than 750 constraints come with the UML metamodel. As the metamodel evolves, its OCL constraints may need to be co-evolved too. Our systematic analysis shows that semantically different resolutions can be applied depending not only on the metamodel changes, but also on the user intent and on the structure of the impacted constraints. In this paper, we investigate the reasons that lead to apply different resolutions. We then propose a co-evolution approach that offers alternative resolutions while allowing the user to choose the best applicable one. We evaluated our approach on the evolution of the UML case study. The results confirm the need of alternative resolutions along with user decision to cope with real co-evolution scenarios. The results show that our approach reaches 80i?ź% of semantically correct co-evolution.

Towards a Better Understanding of Software Features and Their Characteristics: A Case Study of Marlin

The notion of features is commonly used to describe, structure, and communicate the functionalities of a system. Unfortunately, features and their locations in software artifacts are rarely made explicit and often need to be recovered by developers. To this end, researchers have conceived automated feature-location techniques. However, their accuracy is generally low, and they mostly rely on few information sources, disregarding the richness of modern projects. To improve such techniques, we need to improve the empirical understanding of features and their characteristics, including the information sources that support feature location. Even though, the product-line community has extensively studied features, the focus was primarily on variable features in preprocessor-based systems, largely side-stepping mandatory features, which are hard to identify. We present an exploratory case study on identifying and locating features. We study what information sources reveal features and to what extent, compare the characteristics of mandatory and optional features, and formulate hypotheses about our observations. Among others, we find that locating features in code requires substantial domain knowledge for half of the mandatory features (e.g., to connect keywords) and that mandatory and optional features in fact differ. For instance, mandatory features are less scattered. Other researchers can use our manually created data set of features locations for future research, guided by our formulated hypotheses.

Practices and perceptions of UML use in open source projects

Context: Open Source is getting more and more collaborative with industry. At the same time, modeling is today playing a crucial role in development of, e.g., safety critical software. Goal: However, there is a lack of research about the use of modeling in Open Source. Our goal is to shed some light into the motivation and benefits of the use of modeling and its use within project teams. Method: In this study, we perform a survey among Open Source developers. We focus on projects that use the Unified Modeling Language (UML) as a representative for software modeling. Results: We received 485 answers of contributors of 458 different Open Source projects. Conclusion: Collaboration seems to be the most important motivation for using UML. It benefits new contributors and contributors who do not create models. Teams use UML during communication and planning of joint implementation efforts.