Correctness-by-Construction (CbC) is an incremental program construction process to construct functionally correct programs. The programs are constructed stepwise along with a specification that is inherently guaranteed to be satisfied. CbC is complex to use without specialized tool support, since it needs a set of predefined refinement rules of fixed granularity which are additional rules on top of the programming language. Each refinement rule introduces a specific programming statement and developers cannot depart from these rules to construct programs. CbC allows to develop software in a structured and incremental way to ensure correctness, but the limited flexibility is a disadvantage of CbC. In this work, we compare classic CbC with CbC-Block and TraitCbC. Both approaches CbC-Block and TraitCbC, are related to CbC, but they have new language constructs that enable a more flexible software construction approach. We provide for both approaches a programming guideline, which similar to CbC, leads to well-structured programs. CbC-Block extends CbC by adding a refinement rule to insert any block of statements. Therefore, we introduce CbC-Block as an extension of CbC. TraitCbC implements correctness-by-construction on the basis of traits with specified methods. We formally introduce TraitCbC and prove soundness of the construction strategy. All three development approaches are qualitatively compared regarding their programming constructs, tool support, and usability to assess which is best suited for certain tasks and developers.

Security-critical software applications contain confidential information which has to be protected from leaking to unauthorized systems. With language-based techniques, the confidentiality of applications can be enforced. Such techniques are for example type systems that enforce an information flow policy through typing rules. The precision of such type systems, especially in object-oriented languages, is an area of active research: an appropriate system should not reject too many secure programs while soundly preserving noninterference. In this work, we introduce the language SIFO which supports information flow control for an object-oriented language with type modifiers. Type modifiers increase the precision of the type system by utilizing immutability and uniqueness properties of objects for the detection of information leaks. We present SIFO informally by using examples to demonstrate the applicability of the language, formalize the type system, prove noninterference, implement SIFO as a pluggable type system in the programming language L42, and evaluate it with a feasibility study and a benchmark.

Cyber-physical systems are ubiquitous nowadays. However, as automation increases, modeling and verifying them becomes increasingly difficult due to the inherently complex physical environment. Skill graphs are a means to model complex cyber-physical systems (e.g., vehicle automation systems) by distributing complex behaviors among skills with interfaces between them. We identified that skill graphs have a high potential to be amenable to scalable verification approaches in the early software development process. In this work, we suggest combining skill graphs with hybrid programs. Hybrid programs constitute a program notation for hybrid systems enabling the verification of cyber-physical systems. We provide the first formalization of skill graphs including a notion of compositionality and propose Skeditor , an integrated framework for modeling and verifying them. Skeditor is coupled with the theorem prover KeYmaera X , which is specialized in the verification of hybrid programs. In an experiment exhibiting the follow mode of a vehicle, we evaluate our skill-based methodology with respect to savings in verification effort and potential to find modeling defects at design time. Compared to non-compositional verification, the initial verification effort needed is reduced by more than 53%.

Software product lines are increasingly used to handle the growing demand of custom-tailored software variants. They provide systematic reuse of software paired with variability mechanisms in the code to implement whole product families rather than single software products. A common domain of application for product lines are safety-critical systems, which require behavioral correctness to avoid dangerous situations in-field. While most approaches concentrate on post-hoc verification for product lines, we argue that a stepwise approach to create correct programs may be beneficial for developers to manage the growing variability. Correctness-by-construction is such a stepwise approach to create programs using a set of small, tractable refinement rules that guarantee the correctness of the program with regard to its specification. In this paper, we propose the first approach to develop correct-by-construction software product lines using feature-oriented programming. First, we extend correctness-by-construction by two refinement rules for variation points in the code. Second, we give a proof for the soundness of the proposed rules. Third, we implement our technique in a tool called VarCorC and show the applicability of the tool by conducting two case studies.

Correctness-by-Construction (CbC) is an approach to incrementally create formally correct programs guided by pre- and postcondition specifications. A program is created using refinement rules that guarantee the resulting implementation is correct with respect to the specification. Although CbC is supposed to lead to code with a low defect rate, it is not prevalent, especially because appropriate tool support is missing. To promote CbC, we provide tool support for CbC-based program development. We present CorC, a graphical and textual IDE to create programs in a simple while-language following the CbC approach. Starting with a specification, our open source tool supports CbC developers in refining a program by a sequence of refinement steps and in verifying the correctness of these refinement steps using the theorem prover KeY. We evaluated the tool with a set of standard examples on CbC where we reveal errors in the provided specification. The evaluation shows that our tool reduces the verification time in comparison to post-hoc verification.

The analysis of software product lines is challenging due to the potentially large number of products, which grow exponentially in terms of the number of features. Product sampling is a technique used to avoid exhaustive testing, which is often infeasible. In this paper, we propose a classification for product sampling techniques and classify the existing literature accordingly. We distinguish the important characteristics of such approaches based on the information used for sampling, the kind of algorithm, and the achieved coverage criteria. Furthermore, we give an overview on existing tools and evaluations of product sampling techniques. We share our insights on the state-of-the-art of product sampling and discuss potential future work.