Embedded Systems Architecture: Evaluation and Analysis

Large systems often have a long life-span and their system and software architecture design comprise many intricately related elements. The verification and maintenance of these architecture designs require an understanding of how and why the system are constructed. Design rationale is the reasoning behind a design and it provides an explanation of the design. However, the reasoning is often undocumented or unstructured in practice. This causes difficulties in the understanding of the original design, and makes it hard to detect inconsistencies, omissions and conflicts without any explanations to the intricacies of the design. Research into design rationale in the past has focused on argumentation-based design deliberations. Argumentation-based design rationale models provide an explicit representation of design rationale. However, these methods are ineffective in communicating design reasoning in practice because they do not support tracing to design elements and requirements in an effective manner. In this thesis, we firstly report a survey of practising architects to understand their perception of the value of design rationale and how they use and document this knowledge. From the survey, we have discovered that practitioners recognize the importance of documenting design rationale and frequently use them to reason about their design choices. However, they have indicated certain barriers to the use and documentation of design rationale. The results have indicated that there is no systematic approach to using and capturing design rationale in current architecture design practice. Using these findings, we address the issues of representing and applying architecture design rationale. We have constructed a rationale-based architecture model to represent design rationale, design objects and their relationships, which we call Architecture Rationale and Element Linkage (AREL). AREL captures both qualitative and quantitative rationale for architecture design. Quantitative rationale uses costs, benefits and risks to justify architecture decisions. Qualitative rationale documents the issues, arguments, alternatives and tradeoffs of a design decision. With the quantitative and qualitative rationale, the AREL model provides reasoning support to explain why architecture elements exist and what assumptions and constraints they depend on. Using a causal relationship in the AREL model, architecture decisions and architecture elements are linked together to explain the reasoning of the architecture design. Architecture Rationalisation Method (ARM) is a methodology that makes use of AREL to facilitate architecture design. ARM uses cost, benefit and risk as fundamental elements to rank and compare alternative solutions in the decision making process. Using the AREL model, we have proposed traceability and probabilistic techniques based on Bayesian Belief Networks (BBN) to support architecture understanding and maintenance. These techniques can help to carry out change impact analysis and rootcause analysis. The traceability techniques comprise of forward, backward and evolution tracings. Architects can trace the architecture design to discover the change impacts by analysing the qualitative reasons and the relationships in the architecture design. We have integrated BBN to AREL to provide an additional method where probability is used to evaluate and reason about the change impacts in the architecture design. This integration provides quantifiable support to AREL to perform predictive, diagnostic and combined reasoning. In order to align closely with industry practices, we have chosen to represent the rationale-based architecture model in UML. In a case study, the AREL model is applied retrospectively to a real-life bank payment systems to demonstrate its features and applications. Practising architects who are experts in the electronic payment system domain have been invited to evaluate the case study. They have found that AREL is useful in helping them understand the system architecture when they compared AREL with traditional design specifications. They have commented that AREL can be useful to support the verification and maintenance of the architecture because architects do not need to reconstruct or second-guess the design reasoning. We have implemented an AREL tool-set that is comprised of commercially available and custom-developed programs. It enables the capture of architecture design and its design rationale using a commercially available UML tool. It checks the well-formedness of an AREL model. It integrates a commercially available BBN tool to reason about the architecture design and to estimate its change impacts.

Thorough and continuous architecting is the key to overall success in software engineering, and architecture evaluation is a crucial part of it. This tutorial presents a pragmatic architecture evaluation approach and insights gained from its application in more than 75 projects with industrial customers in the past decade. It presents context factors, empirical data, and example cases, as well as lessons learned on mitigating the risk of change through architecture evaluation. By providing comprehensive answers to many typical questions and discussing more frequent mistakes and lessons learned, the tutorial allows the audience to not only learn how to conduct architecture evaluations and interpret its results, but also to become aware of risks such as false conclusions, manipulating data, and unsound lines of argument. It equips the audience to become confident in assessing quantitative measurement results and recognize when it is better to rely on qualitative expertise. The target audience includes both practitioners and researchers. By demonstrating its impact and providing clear guidelines, data, and examples, it encourages practitioners to conduct architecture evaluations. At the same time, it offers researchers insights into industrial architecture evaluations, which serve as the basis for guiding research in this area and will inspire future research directions. Both groups will get an overview of the foundations and history of architecture evaluation. The tutorial covers the following important aspects of architecture evaluation • Architecture drivers: types of drivers, importance of drivers, elicitation of drivers, documentation of drivers as architecture scenarios • Solution Adequacy Check: check whether an architecture is adequate for its drivers, what are risks, assumptions, tradeoffs (based on ATAM (architecture tradeoff analysis method) and enhanced with other techniques for increasing confidence of results) • Documentation Quality Check: How adequate is the documentation of an architecture to be understandable and to serve its purposes? • Architecture Compliance Check: How to check whether an intended architecture is consistently reflected in the source code? For all aspects, pragmatic methodical support is provided in the tutorial and all checks are well integrated in the overall architecture evaluation method.

Research into design rationale in the past has focused on the representation of reasons and has omitted the connections between design rationales and design artefacts. Without such connections, designers and architects cannot easily assess how changing requirements or designs may affect the system. In this paper, we introduce a model called Architecture Rationale and Element Linkage (AREL) to represent the causal relationship between architecture elements and decisions. We further model AREL as a Bayesian Belief Network (BBN) to capture the probabilistic relationships between architecture elements and decisions in an architecture design model. Such probabilistic modelling enables architects to quantitatively predict and diagnose impact of change when part of the requirements or designs are changing. Using a partial design of a cheque image processing system, we illustrate how AREL is used to represent the decision model and how BBN is used to predict and diagnose change in the architecture design. We use a UML tool to capture the AREL model and a BBN tool to compute the probabilities of change impact.

In software architecture design, we explore design alternatives and make decisions about adoption or rejection of a design from a web of complex and often uncertain information. Different architectural design decisions may lead to systems that satisfy the same set of functional requirements but differ in certain quality attributes. In this paper, we propose a Bayesian Network based approach to rational architectural design. Our Bayesian Network helps software architects record and make design decisions. We can perform both qualitative and quantitative analysis over the Bayesian Network to understand how the design decisions influence system quality attributes, and to reason about rational design decisions. We use the KWIC (Key Word In Context) example to illustrate the principles of our approach.

In software architectures, architectural design decisions (ADDs) strongly influence the quality of the resulting software system. Wrong decisions lead to low-quality systems and are difficult to repair later on in the development process. As of today, little is known about the impact of certain ADDs for the development of architectures for blockchain-based systems. Thus, it is difficult to predict the outcome of certain ADDs when developing architectures for such systems. In the following, we propose a simulation-based approach for blockchain architectures in which the impact of certain ADDs on certain quality attributes can be simulated. To this end, we first implemented a simulation environment for blockchain architectures. The simulation environment was then used to execute a series of experiments from which we derived a set of hypotheses about the impact of certain ADDs on quality attributes for blockchain architectures. Finally, we tested the hypotheses using statistical analyses and derived an empirical model for blockchain architectures based on the outcome of the analysis. The model can be used by architects to predict the effect of certain decisions in the design of blockchain architectures before implementing them.

The architecture of a software system is both a success and a failure factor. Taking the wrong architectural decisions may break a project, since such errors are often systematic and affect cross-cutting aspects of the system to be built. Moreover, software projects get more and more challenging due to the rising complexity and dynamics of business processes, large team size and distributed development. As the software architecture is the common platform for many project activities, it constitutes a critical success factor. Thus, a comprehensive method for evaluating a software architecture and propagating important properties of it downstream to code is needed. At sd&m, we designed a comprehensive architecture evaluation and management framework in order to satisfy these needs. In this paper, we derive a list of requirements, such a framework should fulfill. We then present the components of our architecture evaluation method and demonstrate, how it fulfills these requirements.

System quality attributes (QAs) are often considered as the most important decision drivers. In this paper, motivated by the decision making in a smart-city software ecosystem, we extend our previous approach that integrates reusable architectural design decisions (ADDs) with the QAs, by integrating tactics that support quality-driven decision making. In addition, we present an approach that enables system evolution, based on controlled and adaptable decision making and utilizing real data obtained during system monitoring. The approach integrates the previous approach that uses tactics with the existing model-driven development paradigm and the corresponding tools.

The benefits of a software system are assessable only relative to the business goals the system has been developed to serve. In turn, these benefits result from interactions between the system's functionality and its quality attributes (such as performance, reliabilty and security). Its quality attributes are, in most cases, dictated by its architectural design decisions. Therefore, we argue in this paper that the software architecture is the crucial artifact to study in making design tradeoffs and in performing cost-benefit analyses. A substantial part of such an analysis is in determining the level of uncertainty with which we estimate both costs and benefits. In this paper we offer an architecture-centric approach to the economic modeling of software design decision making called CBAM (Cost Benefit Analysis Method), in which costs and benefits are traded off with system quality attributes. We present the CBAM, the early results from applying this method in a large-scale case study, and discuss the application of more sophisticated economic models to software decision making.

The Architecture Design and Evaluation Method for Eco-Sustainabability Oriented Next Generation Communication Networks

The emergence of service-oriented architecture (SOA) as an approach for integrating applications that expose services presents many new challenges to organizations resulting in significant risks to their business. Particularly important among those risks are failures to effectively address quality attribute requirements such as performance, availability, security, and modifiability. Because the risk and impact of SOA is distributed and pervasive across applications, it is critical to perform an architecture evaluation early in the software life cycle. This report contains technical information about SOA design considerations and tradeoffs that can help the architecture evaluator to identify and mitigate risks in a timely and effective manner. The report provides an overview of SOA, outlines key architecture approaches and their effect on quality attributes, establishes an organized collection of design-related questions that an architecture evaluator may use to analyze the ability of the architecture to meet quality requirements, and provides a brief sample evaluation.

ADHD and misophonia are developmental neurological disorders that are currently increasing in prevalence due to excessive acoustic and visual pollution. ADHD, which is characterized by a lack of attention and excessive impulsive hyperactivity, and misophonia, which is hypersensitivity to sounds accompanied by a severe emotional and psychological reaction, are both affected by the user’s spatial environment to a great extent. Spatial design can contribute to increasing or decreasing these unfavorable sensory triggers that affect individuals with ADHD and/or Misophonia. However, the role of architectural spatial design as a therapeutic approach to alleviate the symptoms of Misophonia and ADHD has never been proposed before in the literature, despite its accumulative and chronic effects on the user’s experience in everyday life in terms of well-being and productivity. Therefore, the current work discusses this problem of neglecting the potential effect of architectural spatial design on alleviating Misophonia and ADHD. Thus, the objective of the current work is to propose customized architectural spatial design as a therapeutic approach to alleviate Misophonia and ADHD through adopting the compatible architectural trends of minimal and metaphysical architecture. The methodology of the current work includes a theoretical proposal of this customized architectural spatial design for alleviating these two special neurological conditions. This includes introducing and analyzing these two neurological conditions and their relation to and interaction with architectural spatial design, analyzing minimal and metaphysical architectural trends employed in the proposed therapeutic architectural design, and then proposing augmented and virtual reality as auxiliary add-ons to the architectural spatial design to boost its therapeutic effect. Minimal architecture achieves the “no emotion” criteria through reduced forms, patterns, and colors and adopts simple geometry and natural materials to reduce sensory stressors or stimuli, in order to alleviate the loss of attention and distraction prevalent in those with ADHD, as well as allowing the employment of acoustic materials to achieve acoustic comfort and noise blockage for Misophonia relief. Metaphysical architecture leads the hierarchy of sensory experience through the symbolistic, dynamic, and enigmatic composition of forms and colors, which enhance the spatial analysis and cognitive capacities of the inhabitants. Meanwhile, the use of customized virtual and augmented reality environments is an effective add-on to minimal and metaphysical architectural spaces thanks to its proven therapeutic effect in alleviating various neurological disorders and injuries. At this level of intervention, VR/AR can be used as an add-on to minimal-architecture design, to simulate varied scenarios, as minimal design offers a clean canvas for simulating these varied virtual environments. The other option is to build these customized VR/AR scenarios around a specific architectural element as an add-on metaphysical architecture design to lead the sensory experience and enable the user to detach from the physical constraints of the space. AI-generated designs were used as a proof of concept for the proposed customized architectural spatial design following minimal and metaphysical architecture, as well as to provide AR and VR scenarios as add-on architecture to enhance the therapeutic effect of these architectural spaces for Misophonia and ADHD patients. Furthermore, the validity of VR/AR as a therapeutic approach, alongside the customized architectural design, was discussed, and it was concluded that this study proves the need for extended clinical studies on its efficiency in the long run, which will be conducted in the future.

Visualization of architectural design decision (ADD) and its rationale, as a kind of traceability information, is supposed to facilitate the understanding of architecture design and the reasoning behind the design rationale, which is supposed to improve the architecting process and gets better architecture design results. But the lack of empirical evaluation that supports this statement prevents industrial practitioners from using ADD visualization in their daily architecting activities. In this paper, we conducted a controlled experiment to investigate how visualization of ADD can improve the understanding of architecture design by using Compendium, an open source tool for rationale visualization. The preliminary results show that visualization of ADD and its rationale does not increase the total time for reading architecture document (including visualization diagrams of ADDs) plus designing task, and it improves the understanding of architects on existing architecture design with better new design results.

Metric-based Evaluation of Implemented Software Architectures

Mobile devices are widely accepted as a convergence machine providing both software functionality and cell phone capability. However, they have limited resources such as memory, processing power, and battery. Consequently, complex applications could not be deployed on the devices. An effective solution is to offload some functionality to more powerful servers and to run then on the servers, to yield improved performance and low resource consumption. In this paper, we propose a systematic process for designing mobile applications with full and partial offloading. And, we present schemes to quantitatively evaluate the resulting architecture. Using the proposed architecture design and evaluation methods, mobile applications with loading can be more systematically developed.

Since the architecture of a software system constrains the quality attributes, the decisions taken during architectural design have a large impact on the resulting system. An architectural design method is presented that employs iterative evaluation and transformation of the software architecture in order to satisfy the quality requirements. Architecture evaluation is performed by using scenarios, simulation, mathematical modelling and experience-based reasoning. The architecture can be transformed by imposing an architectural style, imposing an architectural pattern, using a design pattern, converting a quality requirement to functionality and by distributing quality requirements. The method has evolved through its application in several industrial projects.