Comparative Analysis of Architectural Views Based on UML

The need to model systems and their different aspects leads to research and development of models which support all views of a system. The growing complexity of the software imposes the use of architectures, not only because we want to build accurate systems, but also because we need to understand them. Separating aspects of different views usually helps us to manage software complexity. The current work is an analysis of two important approaches on architectural views and on the use of UML to reason about views. Our goal is to analyze the different aspects addressed by them and how UML is inserted on each of these models.     

Understanding the role of licenses and evolution in open architecture software ecosystems

The role of software ecosystems in the development and evolution of open architecture systems whose components are subject to different licenses has received insufficient consideration. Such systems are composed of components potentially under two or more licenses, open source or proprietary or both, in an architecture in which evolution can occur by evolving existing components, replacing them, or refactoring. The software licenses of the components both facilitate and constrain the system's ecosystem and its evolution, and the licenses’ rights and obligations are crucial in producing an acceptable system. Consequently, software component licenses and the architectural composition of a system help to better define the software ecosystem niche in which a given system lies. Understanding and describing software ecosystem niches for open architecture systems is a key contribution of this work. An example open architecture software system that articulates different niches is employed to this end. We examine how the architecture and software component licenses of a composed system at design time, build time, and run time help determine the system's software ecosystem niche and provide insight and guidance for identifying and selecting potential evolutionary paths of system, architecture, and niches.     

A review and future directions of SOA-based software architecture modeling approaches for System of Systems

Software architecture is a software system’s earliest set of design decisions that are critical for the quality of the system desired by the stakeholders. The architecture makes it easier to reason about and manage change during different phases of complex software life cycle. The modeling of software architecture for System of Systems (SoS) is a challenging task because of a system’s complexity arising from an integration of heterogeneous, distributed, managerially and operationally independent systems collaborating to achieve global missions. SoS is essentially dynamic and evolutionary by design requiring suitable architectural patterns to deal with runtime volatility. Service-oriented architecture offers several architectural features to these complex systems; these include, interoperability, loose coupling, abstraction and the provision of dynamic services based on standard interfaces and protocols. There is some research work available that provides critical analysis of current software architecture modeling approaches for SoS. However, none of them outlines the important characteristics of SoS or provides detailed analysis of current service-oriented architecture modeling approaches to model those characteristics. This article addresses this research gap and provides a taxonomy of software architecture modeling approaches, comparing and contrasting them using criteria critical for realization of SoS. Additionally, research gaps are identified, and future directions are outlined for building software architecture for SoS to model and reason about architecture quality in a more efficient way in service-oriented paradigm.     

An architectural approach to the correct and automatic assembly of evolving component-based systems

Software components are specified, designed and implemented with the intention to be reused, and they are assembled in various contexts in order to produce a multitude of software systems. However, in the practice of software development, this ideal scenario is often unrealistic. This is mainly due to the lack of an automatic and efficient support to predict properties of the assembly code by only assuming a limited knowledge of the properties of single components. Moreover, to make effective the component-based vision, the assembly code should evolve when things change, i.e., the properties guaranteed by the assembly, before a change occurs, must hold also after the change. Glue code synthesis approaches technically permit one to construct an assembly of components that guarantees specific properties but, practically, they may suffer from the state-space explosion phenomenon.In this paper, we propose a Software Architecture (SA) based approach in which the usage of the system SA and of SA verification techniques allows the system assembler to design architectural components whose interaction is verified with respect to the specified properties. By exploiting this validation, the system assembler can perform code synthesis by only focusing on each single architectural component, hence refining it as an assembly of actual components which respect the architectural component observable behaviour. In this way code synthesis is performed locally on each architectural component, instead of globally on the whole system interactions, hence reducing the state-space explosion phenomenon.The approach can be equally well applied to efficiently manage the whole reconfiguration of the system when one or more components need to be updated, still maintaining the required properties. The specified and verified system SA is used as starting point for the derivation of glue adaptors that are required to apply changes in the composed system. The approach is firstly illustrated over an explanatory example and is then applied and validated over a real-world industrial case study.     

A large-scale study of architectural evolution in open-source software systems

From its very inception, the study of software architecture has recognized architectural decay as a regularly occurring phenomenon in long-lived systems. Architectural decay is caused by repeated, sometimes careless changes to a system during its lifespan. Despite decay’s prevalence, there is a relative dearth of empirical data regarding the nature of architectural changes that may lead to decay, and of developers’ understanding of those changes. In this paper, we take a step toward addressing that scarcity by introducing an architecture recovery framework, ARCADE, for conducting large-scale replicable empirical studies of architectural change across different versions of a software system. ARCADE includes two novel architectural change metrics, which are the key to enabling large-scale empirical studies of architectural change. We utilize ARCADE to conduct an empirical study of changes found in software architectures spanning several hundred versions of 23 open-source systems. Our study reveals several new findings regarding the frequency of architectural changes in software systems, the common points of departure in a system’s architecture during the system’s maintenance and evolution, the difference between system-level and component-level architectural change, and the suitability of a system’s implementation-level structure as a proxy for its architecture.     

Evolving information systems: meeting the ever-changing environment

Abstract. To meet the demands of organizations and their ever-changing environment, information systems are required which are able to evolve to the same extent as organizations do. Such a system has to support changes in all time-and application-dependent aspects. In this paper, requirements and a conceptual framework for evolving information systems are presented. This framework includes an architecture for such systems and a revision of the traditional notion of update. Based on this evolutionary notion of update (recording, correction and forgetting) a state transition-oriented model on three levels of abstraction (event level, recording level, correction level) is introduced. Examples are provided to illustrate the conceptual framework for evolving information systems.     

Mining Patterns from Change Logs to Support Reuse-Driven Evolution of Software Architectures

Modern software systems are subject to a continuous evolution under frequently varying requirements and changes in systems’ operational environments. Lehman’s law of continuing change demands for long-living and continuously evolving software to prolong its productive life and economic value by accommodating changes in existing software. Reusable knowledge and practices have proven to be successful for continuous development and evolution of the software effectively and efficiently. However, challenges such as empirical acquisition and systematic application of the reusable knowledge and practices must be addressed to enable or enhance software evolution. We investigate architecture change logs — mining histories of architecture-centric software evolution — to discover change patterns that 1) support reusability of architectural changes and 2) enhance the efficiency of the architecture evolution process. We model architecture change logs as a graph and apply graph-based formalism (i.e., graph mining techniques) to discover software architecture change patterns. We have developed a prototype that enables tool-driven automation and user decision support during software evolution. We have used the ISO-IEC-9126 model to qualitatively evaluate the proposed solution. The evaluation results suggest that the proposed solution 1) enables the reusability of frequent architectural changes and 2) enhances the efficiency of architecture-centric software evolution process. The proposed solution promotes research efforts to exploit the history of architectural changes to empirically discover knowledge that can guide architecture-centric software evolution.     

An Empirical Study of Lehman''s Law on Software Quality Evolution

Software systems must change to adapt to new functional requirements and nonfunctional requirements. According to Lehman''s laws of software evolution, on the one side, the size and the complexity of a software system will continually increase in its life time; on the other side, the quality of a software system will decrease unless it is rigorously maintained and adapted. Lehman''s laws of software evolution, especially of those on software size and complexity, have been widely validated. However, there are few empirical studies of Lehman''s law on software quality evolution, despite the fact that quality is one of the most important measurements of a software product. This paper defines a metric---accumulated defect density---to measure the quality of evolving software systems. We mine the bug reports and measure the size and complexity growth of four evolution lines of Apache Tomcat and Apache Ant projects. Based on these studies, Lehman''s law on software quality evolution is examined and evaluated.     

Dependency solving: A separate concern in component evolution management

Maintenance of component-based software platforms often has to face rapid evolution of software components. Component dependencies, conflicts, and package managers with dependency solving capabilities are the key ingredients of prevalent software maintenance technologies that have been proposed to keep software installations synchronized with evolving component repositories. We review state-of-the-art package managers and their ability to keep up with evolution at the current growth rate of popular component-based platforms, and conclude that their dependency solving abilities are not up to the task.We show that the complexity of the underlying upgrade planning problem is NP-complete even for seemingly simple component models, and argue that the principal source of complexity lies in multiple available versions of components. We then discuss the need of expressive languages for user preferences, which makes the problem even more challenging.We propose to establish dependency solving as a separate concern from other upgrade aspects, and present CUDF as a formalism to describe upgrade scenarios. By analyzing the result of an international dependency solving competition, we provide evidence that the proposed approach is viable.     

A survey of evolutionary and embryogenic approaches to autonomic networking

The term “autonomic networking” refers to network-level software systems capable of self-management, according to the principles outlined by the Autonomic Computing initiative. Autonomicity is widely recognized as a crucial property to harness the growing complexity of current networked systems.In this paper, we present a review of state-of-the-art techniques for the automated creation and evolution of software, with application to network-level functionalities. The main focus of the survey are biologically-inspired bottom-up approaches, in which complexity is grown from interactions among simpler units. First, we review evolutionary computation, highlighting aspects that apply to the automatic optimization of computer programs in online, dynamic environments. Then, we review chemical computing, discussing its suitability as execution model for autonomic software undergoing self-optimization by code rewriting. Last, we survey approaches inspired by embryology, in which artificial entities undergo a developmental process. The overview is completed by an outlook into the major technical challenges for the application of the surveyed techniques to autonomic systems.     

A Rigorous Architectural Approach to Adaptive Software Engineering

The engineering of distributed adaptive software is a complex task which requires a rigorous approach. Software architectural (structural) concepts and principles are highly beneficial in specifying, designing, analysing, constructing and evolving distributed software. A rigorous architectural approach dictates formalisms and techniques that are compositional, components that are context independent and systems that can be constructed and evolved incrementally. This paper overviews some of the underlying reasons for adopting an architectural approach, including a brief “rational history” of our research work, and indicates how an architectural model can potentially facilitate the provision of self-managed adaptive software system. Much of the research has been supported by the Engineering and Physical Sciences Research Council and is currently partly supported by EPSRC Platform grant AEDUS 2 and a DTC grant.     

Information systems development: a perspective on the challenge of evolutionary complexity

This conceptual paper proposes that the methodical approach to information system development leads us to design systems that are unable to deal with the challenge of evolutionary complexity. This is examined through the use of a systemic framework that describes evolutionary complexity in terms of interaction between the concepts of distinction/connection and variation/selection. In applying these concepts to the social world we are led to conclude (a) that social regularities are emergent and not a priori given and (b) that these emergent regularities are constantly shifting and evolving. This has strong implications for the methodical approach to development, which we argue assumes social structures, mechanisms and processes as ‘invariant regularities’ that only have to be revealed to be understood. This difference leads methodical development to produce static systems that have to work in a dynamic world. The paper concludes by outlining a proposition in response to the challenge of evolutionary complexity, one where design is considered as an inherently ongoing process.     

Developing and evolving a DSL-based approach for runtime monitoring of systems of systems

Complex software-intensive systems are often described as systems of systems (SoS) due to their heterogeneous architectural elements. As SoS behavior is often only understandable during operation, runtime monitoring is needed to detect deviations from requirements. Today, while diverse monitoring approaches exist, most do not provide what is needed to monitor SoS, e.g., support for dynamically defining and deploying diverse checks across multiple systems. In this paper we report on our experiences of developing, applying, and evolving an approach for monitoring an SoS in the domain of industrial automation software, that is based on a domain-specific language (DSL). We first describe our initial approach to dynamically define and check constraints in SoS at runtime and then motivate and describe its evolution based on requirements elicited in an industry collaboration project. We furthermore describe solutions we have developed to support the evolution of our approach, i.e., a code generation approach and a framework to automate testing the DSL after changes. We evaluate the expressiveness and scalability of our new DSL-based approach using an industrial SoS. We also discuss lessons we learned. Our results show that while developing a DSL-based approach is a good solution to support industrial users, one must prepare the approach for evolution, by making it extensible and adaptable to future scenarios. Particularly, support for automated (re-)generation of tools and code after changes and automated testing are essential.     

Deriving software architectural models from requirements models for adaptive systems: the STREAM-A approach

Some quality attributes are known to have an impact on the overall architecture of a system, so that they are required to be properly handled from the early beginning of the software development. For example, adaptability is a key concern for autonomic and adaptive systems, which brings to them the capability to alter their behavior in response to changes on their surrounding environments. In this paper, we propose a Strategy for Transition between Requirements and Architectural Models for Adaptive systems (STREAM-A). In particular, we use goal models based on the i* (i-Star) framework to support the design and evolution of systems that require adaptability. To obtain software architectures for such systems, the STREAM-A approach uses model transformations from i* models to architectural models expressed in Acme. Both the requirements and the architectural model are refined to accomplish the adaptability requirement.     

Stability assessment of aspect-oriented software architectures: A quantitative study

Design of stable software architectures has increasingly been a deep challenge to software developers due to the high volatility of their concerns and respective design decisions. Architecture stability is the ability of the high-level design units to sustain their modularity properties and not succumb to modifications. Architectural aspects are new modularity units aimed at improving design stability through the modularization of otherwise crosscutting concerns. However, there is no empirical knowledge about the positive and negative influences of aspectual decompositions on architecture stability. This paper presents an exploratory analysis of the influence exerted by aspect-oriented composition mechanisms in the stability of architectural modules addressing typical crosscutting concerns, such as error handling and security. Our investigation encompassed a comparative analysis of aspectual and non-aspectual decompositions based on different architectural styles applied to an evolving multi-agent software architecture. In particular, we assessed various facets of components’ and compositions’ stability through such alternative designs of the same multi-agent system using conventional quantitative indicators. We have also investigated the key characteristics of aspectual decompositions that led to (in)stabilities being observed in the target architectural options. The evaluation focused upon a number of architecturally-relevant changes that are typically performed through real-life maintenance tasks.     

Semi-automated architectural abstraction specifications for supporting software evolution

In this paper we present an approach for supporting the semi-automated architectural abstraction of architectural models throughout the software life-cycle. It addresses the problem that the design and implementation of a software system often drift apart as software systems evolve, leading to architectural knowledge evaporation. Our approach provides concepts and tool support for the semi-automatic abstraction of architecture component and connector views from implemented systems and keeping the abstracted architecture models up-to-date during software evolution. In particular, we propose architecture abstraction concepts that are supported through a domain-specific language (DSL). Our main focus is on providing architectural abstraction specifications in the DSL that only need to be changed, if the architecture changes, but can tolerate non-architectural changes in the underlying source code. Once the software architect has defined an architectural abstraction in the DSL, we can automatically generate architectural component views from the source code using model-driven development (MDD) techniques and check whether architectural design constraints are fulfilled by these models. Our approach supports the automatic generation of traceability links between source code elements and architectural abstractions using MDD techniques to enable software architects to easily link between components and the source code elements that realize them. It enables software architects to compare different versions of the generated architectural component view with each other. We evaluate our research results by studying the evolution of architectural abstractions in different consecutive versions of five open source systems and by analyzing the performance of our approach in these cases.     

Automatic library migration for the generation of hardware-in-the-loop models

Embedded systems are widely used in several applications nowadays. As they integrate hard- and software elements, their functionality and reliability are often tested by hardware-in-the-loop methods, in which the system under test runs in a simulated environment. Due to the rising complexity of the embedded functions, performance limitations and practicability reasons, the simulations are often specialized to test specific aspects of the embedded system and develop a high diversity by themselves. This diversity is difficult to manage for a user and results in erroneously selected test components and compatibility problems in the test configuration. This paper presents a generative programming approach that handles the diversity of test libraries. Compatibility issues are explicitly evaluated by a new interface concept. Furthermore, a novel model analyzer facilitates the efficient application in practice by migrating existing libraries. The approach is evaluated for an example from the automotive domain using MATLAB/Simulink.