Tim Winkelmann

Multi-perspectives on feature models

Domain feature models concisely express commonality and variability among variants of a software product line. For supporting separation of concerns, e.g., due to legal restrictions, technical considerations and business requirements, multi-view approaches restrict the configuration choices on feature models for different stakeholders. However, recent approaches lack a formalization for precise, yet flexible specifications of views that ensure every derivable configuration perspective to obey feature model semantics. Here, we introduce a novel approach for preconfiguring feature models to create multi-perspectives. Such customized perspectives result from composition of various concern-relevant views. A structured view model is used to organize features in view groups, wherein a feature may be contained in multiple views. We provide formalizations for view composition and guaranteed consistency of perspectives w.r.t. feature model semantics. Thereupon, an efficient algorithm to verify consistency for entire multi-perspectives is provided. We present an implementation and evaluate our concepts by means of various experiments.

Delta-oriented multi software product lines

Modern software systems outgrow the scope of traditional software product lines (SPLs) resulting in multi software product lines (MSPLs) with many interconnected subsystem versions and variants. Delta-oriented programming (DOP) is a flexible, modular approach for implementing SPLs, but DOP so far does not allow the realization of MSPLs. In this paper, we extend DOP to support MSPL development and provide the first holistic modeling approach for MSPLs that spans problem, solution and configuration space. The main concept is the extension of DOP with the possibility to import other SPLs or MSPLs into a new MSPL. By expressing constraints amongst the imported SPLs, a common configuration and product generation is enabled.

Detecting and Explaining Conflicts in Attributed Feature Models.

Product configuration systems are often based on a variability model. The development of a variability model is a time consuming and error-prone process. Considering the ongoing development of products, the variability model has to be adapted frequently. These changes often lead to mistakes, such that some products cannot be derived from the model anymore, that undesired products are derivable or that there are contradictions in the variability model. In this paper, we propose an approach to discover and to explain contradictions in attributed feature models efficiently in order to assist the developer with the correction of mistakes. We use extended feature models with attributes and arithmetic constraints, translate them into a constraint satisfaction problem and explore those for contradictions. When a contradiction is found, the constraints are searched for a set of contradicting relations by the QuickXplain algorithm.

Delta-Trait Programming of Software Product Lines

Delta-oriented programming DOP is a flexible approach for implementing software product lines SPLs. DOP SPLs are implemented by a set of delta modules encapsulating changes to class-based object-oriented programs. A particular product in a DOP SPL is generated by applying to the empty program the modifications contained in the delta modules associated to the selected product features. Traits are pure units of behavior, designed to support flexible fine-grained reuse and to provide an effective means to counter the limitations of class-based inheritance. A trait is a set of methods which is independent from any class hierarchy and can be flexibly used to build other traits or classes by means of a suite of composition operations. In this paper, we present an approach for programming SPLs of trait-based programs where the program modifications expressed by delta modules are formulated by exploiting the trait composition mechanism. This smooth integration of the modularity mechanisms provided by delta modules and traits results in a new approach for programming SPLs, delta-trait programming DTP, which is particularly well suited for evolving SPLs.

Variability Hiding in Contracts for Dependent Software Product Lines

Software product lines are used to efficiently develop and verify similar software products. While they focus on reuse of artifacts between products, a product line may also be reused itself in other product lines. A challenge with such dependent product lines is evolution; every change in a product line may influence all dependent product lines. With variability hiding, we aim to hide certain features and their artifacts in dependent product lines. In prior work, we focused on feature models and implementation artifacts. We build on this by discussing how variability hiding can be extended to specifications in terms of method contracts. We illustrate variability hiding in contracts by means of a running example and share our insights with preliminary experiments on the benefits for formal verification. In particular, we find that not every change in a certain product line requires a re-verification of other dependent product lines.

Automated verification of feature model configuration processes based on workflow Petri nets

Modern software systems are highly configurable in order to satisfy diverse customer requirements and application contexts. Feature models provide a well-established formalism for tailoring configuration spaces of applications. Thereupon, multi-view staged configuration approaches modularize feature models for separation of concerns and apply workflow modeling for scheduling configuration decisions. However, the complex, often oblivious and even cyclic logical dependencies among configuration decisions obstruct compositional semantics of feature model views thus spoiling intuitive modeling and rigorous analysis of staged configuration processes. In this paper, we apply workflow Petri nets (WPNs) as a formal operational model for staged configuration that makes explicit causal dependencies among feature selections. For the internal separation into composable configuration stages we further adopt the principles of open workflow nets. It is shown that the soundness notion of WPNs naturally coincides with fundamental correctness and liveness properties to be verified for staged configuration processes. We present a prototype implementation for an automated computation of staged configuration processes and provide experimental results concerning scalability properties.