Betty H. C. Cheng

Composing adaptive software

Interest in adaptive computing systems has increased dramatically in the past few years, and a variety of techniques now allow software to adapt dynamically to its environment. Compositional adaptation enables software to modify its structure and behavior dynamically in response to change in its execution environment. A review of current technology compares how, when, and where recomposition occurs.

Model-based development of dynamically adaptive software

Increasingly, software should dynamically adapt its behavior at run-time in response to changing conditions in the supporting computing and communication infrastructure, and in the surrounding physical environment. In order for an adaptive program to be trusted, it is important to have mechanisms to ensure that the program functions correctly during and after adaptations. Adaptive programs are generally more difficult to specify, verify, and validate due to their high complexity. Particularly, when involving multi-threaded adaptations, the program behavior is the result of the collaborative behavior of multiple threads and software components. This paper introduces an approach to create formal models for the behavior of adaptive programs. Our approach separates the adaptation behavior and non-adaptive behavior specifications of adaptive programs, making the models easier to specify and more amenable to automated analysis and visual inspection. We introduce a process to construct adaptation models, automatically generate adaptive programs from the models, and verify and validate the models. We illustrate our approach through the development of an adaptive GSM-oriented audio streaming protocol for a mobile computing application.

Real-time specification patterns

Embedded systems are pervasive and frequently used for critical systems with time-dependent functionality. Dwyer et al. (1999) have developed qualitative specification patterns to facilitate the specification of critical properties, such as those that must be satisfied by embedded systems. Thus far, no analogous repository has been compiled for realtime specification patterns. This paper makes two main contributions: First, based on an analysis of timing-based requirements of several industrial embedded system applications, we created real-time specification patterns in terms of three commonly used real-time temporal logics. Second, as a means to further facilitate the understanding of the meaning of a specification, we offer a structured English grammar that includes support for real-time properties. We illustrate the use of the real-time specification patterns in the context of property specifications of a real-world automotive embedded system.

A general framework for formalizing UML with formal languages

Informal and graphical modeling techniques enable developers to construct abstract representations of systems. Object-oriented modeling techniques further facilitate the development process. The Unified Modeling Language (UML), an object-oriented modeling approach, could be broad enough in scope to represent a variety of domains and gain widespread use. Currently, UML comprises several different notations with no formal semantics attached to the individual diagrams. Therefore, it is not possible to apply rigorous automated analysis or to execute a UML model in order to test its behavior: short of writing code and performing exhaustive testing. We introduce a general framework for formalizing a subset of UML diagrams in terms of different formal languages based on a homomorphic mapping between meta models describing UML and the formal language. This framework enables the construction of a consistent set of rules for transforming UML models into specifications in the formal language. The resulting specifications derived from UML diagrams enable either execution through simulation or analysis through model checking, using existing tools. This paper describes the use of this framework for formalisms UML to model and analyze embedded systems. A prototype system for generating the formal specifications and results from an industrial case study are also described.

A formal semantics for object model diagrams

Informal software development techniques, such as the object modeling technique (OMT), provide the user with easy to understand graphical notations for expressing a wide variety of concepts central to the presentation of software requirements. OMT combines three complementary diagramming notations for documenting requirements: object models, dynamic models, and functional models. OMT is a useful organizational tool in the requirements analysis and system design processes. Currently, the lack of formality in OMT prevents the evaluation of completeness, consistency, and content in requirements and design specifications. A formal method is a mathematical approach to software development that begins with the construction of a formal specification describing the system under development. However, constructing a formal specification directly from a prose description of requirements can be challenging. The paper presents a formal semantics for the OMT object model notations, where an object model provides the basis for the architecture of an object oriented system. A method for deriving modular algebraic specifications directly from object model diagrams is described. The formalization of object models contributes to a mathematical basis for deriving system designs. >

RELAX: Incorporating Uncertainty into the Specification of Self-Adaptive Systems

Self-adaptive systems have the capability to autonomously modify their behaviour at run-time in response to changes in their environment. Self-adaptation is particularly necessary for applications that must run continuously, even under adverse conditions and changing requirements; sample domains include automotive systems, telecommunications, and environmental monitoring systems. While a few techniques have been developed to support the monitoring and analysis of requirements for adaptive systems, limited attention has been paid to the actual creation and specification of requirements of self-adaptive systems. As a result, self-adaptivity is often constructed in an ad-hoc manner. In this paper, we argue that a more rigorous treatment of requirements explicitly relating to self-adaptivity is needed and that, in particular, requirements languages for self-adaptive systems should include explicit constructs for specifying and dealing with the uncertainty inherent in self-adaptive systems. We present RELAX, a new requirements language for self-adaptive systems and illustrate it using examples from the smart home domain.

A Goal-Based Modeling Approach to Develop Requirements of an Adaptive System with Environmental Uncertainty

Dynamically adaptive systems (DASs) are intended to monitor the execution environment and then dynamically adapt their behavior in response to changing environmental conditions. The uncertainty of the execution environment is a major motivation for dynamic adaptation; it is impossible to know at development time all of the possible combinations of environmental conditions that will be encountered. To date, the work performed in requirements engineering for a DAS includes requirements monitoring and reasoning about the correctness of adaptations, where the DAS requirements are assumed to exist. This paper introduces a goal-based modeling approach to develop the requirements for a DAS, while explicitly factoring uncertainty into the process and resulting requirements. We introduce a variation of threat modeling to identify sources of uncertainty and demonstrate how the RELAX specification language can be used to specify more flexible requirements within a goal model to handle the uncertainty.

Design patterns for developing dynamically adaptive systems

Increasingly, software systems should self-adapt to satisfy new requirements and environmental conditions that may arise after deployment. Due to their high complexity, adaptive programs are difficult to specify, design, verify, and validate. Moreover, the current lack of reusable design expertise that can be leveraged from one adaptive system to another further exacerbates the problem. We studied over thirty adaptation-related research and project implementations available from the literature and open sources to harvest adaptation-oriented design patterns that support the development of adaptive systems. These adaptation-oriented patterns facilitate the separate development of the functional and adaptive logic. In order to support the assurance of adaptive systems, each design pattern includes templates that formally specify invariant properties of adaptive systems. To demonstrate their usefulness, we have applied a subset of our adaptation-oriented patterns to the design and implementation of ZAP.com, an adaptive news web server.

RELAX: a language to address uncertainty in self-adaptive systems requirement

Self-adaptive systems have the capability to autonomously modify their behavior at run-time in response to changes in their environment. Self-adaptation is particularly necessary for applications that must run continuously, even under adverse conditions and changing requirements; sample domains include automotive systems, telecommunications, and environmental monitoring systems. While a few techniques have been developed to support the monitoring and analysis of requirements for adaptive systems, limited attention has been paid to the actual creation and specification of requirements of self-adaptive systems. As a result, self-adaptivity is often constructed in an ad-hoc manner. In order to support the rigorous specification of adaptive systems requirements, this paper introduces RELAX, a new requirements language for self-adaptive systems that explicitly addresses uncertainty inherent in adaptive systems. We present the formal semantics for RELAX in terms of fuzzy logic, thus enabling a rigorous treatment of requirements that include uncertainty. RELAX enables developers to identify uncertainty in the requirements, thereby facilitating the design of systems that are, by definition, more flexible and amenable to adaptation in a systematic fashion. We illustrate the use of RELAX on smart home applications, including an adaptive assisted living system.

Goal-Based Modeling of Dynamically Adaptive System Requirements

Self-adaptation is emerging as an increasingly important capability for many applications, particularly those deployed in dynamically changing environments, such as ecosystem monitoring and disaster management. One key challenge posed by dynamically adaptive systems (DASs) is the need to handle changes to the requirements and corresponding behavior of a DAS in response to varying environmental conditions. Berry et al. previously identified four levels of RE that should be performed for a DAS. In this paper, we propose the levels of RE for modeling that reify the original levels to describe RE modeling work done by DAS developers. Specifically, we identify four types of developers: the system developer, the adaptation scenario developer, the adaptation infrastructure developer, and the DAS research community. Each level corresponds to the work of a different type of developer to construct goal model(s) specifying their requirements. We then leverage the levels of RE for modeling to propose two complementary processes for performing RE for a DAS. We describe our experiences with applying this approach to GridStix, an adaptive flood warning system, deployed to monitor the River Ribble in Yorkshire, England.