Ragnhild Kobro Runde

STAIRS towards formal design with sequence diagrams

The paper presents STAIRS [1], an approach to the compositional development of UML interactions supporting the specification of mandatory as well as potential behavior. STAIRS has been designed to facilitate the use of interactions for requirement capture as well as test specification. STAIRS assigns a precise interpretation to the various steps in incremental system development based on an approach to refinement known from the field of formal methods and provides thereby a foundation for compositional analysis. An interaction may characterize three main kinds of traces. A trace may be (1) positive in the sense that it is valid, legal or desirable, (2) negative meaning that it is invalid, illegal or undesirable, or (3) inconclusive meaning that it is considered irrelevant for the interaction in question. The basic increments in system development proposed by STAIRS, are structured into three main kinds referred to as supplementing, narrowing and detailing. Supplementing categorizes inconclusive traces as either positive or negative. Narrowing reduces the set of positive traces to capture new design decisions or to match the problem more adequately. Detailing involves introducing a more detailed description without significantly altering the externally observable behavior.

Why timed sequence diagrams require three-event semantics

STAIRS is an approach to the compositional development of sequence diagrams supporting the specification of mandatory as well as potential behavior. In order to express the necessary distinction between black-box and glass-box refinement, an extension of the semantic framework with three event messages is introduced. A concrete syntax is also proposed. The proposed extension is especially useful when describing time constraints. The resulting approach, referred to as Timed STAIRS, is formally underpinned by denotational trace semantics. A trace is a sequence of three kinds of events: events for transmission, reception and consumption. We argue that such traces give the necessary expressiveness to capture the standard UML interpretation of sequence diagrams as well as the black-box interpretation found in classical formal methods.

Approaches for the combined use of risk analysis and testing: a systematic literature review

Risk analysis and testing are conducted for different purposes. Risk analysis and testing nevertheless involve processes that may be combined to the benefit of both. We may use testing to support risk analysis and risk analysis to support testing. This paper surveys literature on the combined use of risk analysis and testing. First, the existing approaches are identified through a systematic literature review. The identified approaches are then classified and discussed with respect to main goal, context of use and maturity level. The survey highlights the need for more structure and rigor in the definition and presentation of approaches. Evaluations are missing in most cases. The paper may serve as a basis for examining approaches for the combined use of risk analysis and testing, or as a resource for identifying the adequate approach to use.

The pragmatics of STAIRS

STAIRS is a method for the compositional development of interactions in the setting of UML 2.0. In addition to defining denotational trace semantics for the main aspects of interactions, STAIRS focuses on how interactions may be developed through successive refinement steps. In this tutorial paper, we concentrate on explaining the practical relevance of STAIRS. Guidelines are given on how to create interactions using the different STAIRS operators, and how these may be refined. The pragmatics is illustrated by a running example.

Underspecification, Inherent Nondeterminism and Probability in Sequence Diagrams

Nondeterminism in specifications may be used for at least two different purposes. One is to express underspecification, which means that the specifier for the same environment behavior allows several alternative behaviors of the specified component and leaves the choice between these to those responsible for implementing the specification. In this case a valid implementation will need to implement at least one, but not necessarily all, alternatives. The other purpose is to express inherent nondeterminism, which means that a valid implementation needs to reflect all alternatives. STAIRS is an approach to the compositional and incremental development of sequence diagrams supporting underspecification as well as inherent nondeterminism. Probabilistic STAIRS builds on STAIRS and allows probabilities to be included in the specifications. Underspecification with respect to probabilities is also allowed. This paper investigates the use of underspecification, inherent nondeterminism and probability in sequence diagrams, the relationships between these concepts, and how these are expressed in STAIRS and probabilistic STAIRS.

Confluence of aspects for sequence diagrams

The last decade has seen several aspect language proposals for UML 2 sequence diagrams. Aspects allow the modeler to define crosscutting concerns of sequence diagrams and to have these woven with the sequence diagrams of a so-called base model, in order to create a woven model. In a real-world scenario, there may be multiple aspects applicable to the same base model. This raises the need to analyse the set of aspects to identify possible aspect interactions (dependencies and conflicts) between applications of aspects. We call a set of aspects terminating if they may not be applied infinitely many times for any given base model. Furthermore, we call a set of terminating aspects confluent, if they, for any given base model, always yield the same final result regardless of the order in which they are applied. Since confluence must hold for any base model, this is a much stronger result than many of the current approaches that have addressed detection of aspect interactions limited to a specific base model. Our aspects are specified using standard sequence diagrams with some extensions. In this paper, we present a confluence theory specialized for our highly expressive aspect language. For the most expressive aspects, we prove that confluence is undecidable. For another class of aspects with considerable expressiveness, we prescribe an algorithm to check confluence. This algorithm is based on what we call an extended critical pair analysis. These results are useful both for modelers and researchers working with sequence diagram aspects and for researchers wanting to establish a confluence theory for other aspect-oriented modelling or model transformation approaches.

Time exceptions in sequence diagrams

UML sequence diagrams partially describe a system. We show how the description may be augmented with exceptions triggered by the violation of timing constraints and compare our approach to those of the UML 2.1 simple time model, the UML Testing Profile and the UML profile for Schedulability, Performance and Time. We give a formal definition of time exceptions in sequence diagrams and show that the concepts are compositional. An ATM example is used to explain and motivate the concepts.

Specifying Service Composition Using UML 2.x and Composition Policies

In the current and future service environment, service parts are being developed separately while being dynamically combined at runtime. In this paper we address the problem of defining a model-driven process for enabling dynamic composition of services. Composition policies are used to define choices in behaviour under which service roles involved in a composite service can be dynamically combined at runtime. We model policy-ruled choreography of collaboration components using a policy enforcement state machine (PESM). We also define transformation rules for translating a global PESM diagram into a set of local PESM diagrams, one for each role. As an example, we consider the case of dynamically composing an existing service with a set of authentication and authorization collaborations. The approach is supported by a formal syntax and semantics.

Stepwise refinement of sequence diagrams with soft real-time constraints

UML sequence diagrams and similar notations are much used to specify and analyze computer systems and their requirements. Probabilities are often essential, in particular for capturing soft real-time constraints. It is also important to be able to specify systems at different levels of abstraction. Refinement is a means to relate abstract specifications to more concrete specifications in such a way that constraints and analysis results are preserved through the transition. In order to allow soft real-time constraints to be included as an integral part of sequence diagram specifications, this paper presents an approach to extend UML 2.x sequence diagrams to capture probabilistic choice in general and soft real-time constraints in particular. The approach is supported by formal semantics and pragmatic refinement relations with mathematical properties that allow stepwise and modular development of specifications. An example focusing on communication is provided to demonstrate the language and refinement relations.

Relating computer systems to sequence diagrams: the impact of underspecification and inherent nondeterminism

Having a sequence diagram specification and a computer system, we need to answer the question: Is the system compliant with the sequence diagram specification in the desired way? We present a procedure for answering this question for sequence diagrams with underspecification and inherent nondeterminism. The procedure is independent of any concrete technology, and relies only on the execution traces that may be produced by the system. If all traces are known, the procedure results in either “compliant” or “not compliant”. If only a subset of the traces is known, the conclusion may also be “likely compliant” or “likely not compliant”.