Jordi Marco

Usage-Based Online Testing for Proactive Adaptation of Service-Based Applications

Increasingly, service-based applications (SBAs) are composed of third-party services available over the Internet. Even if third-party services have shown to work during design-time, they might fail during the operation of the SBA due to changes in their implementation, provisioning, or the communication infrastructure. As a consequence, SBAs need to dynamically adapt to such failures during run-time to ensure that they maintain their expected functionality and quality. Ideally the need for an adaptation is proactively identified, i.e., failures are predicted before they can lead to consequences such as costly compensation and roll-back activities. Currently, approaches to predict failures are based on monitoring. Due to its passive nature, however, monitoring might not cover all relevant service executions, which can diminish the ability to correctly predict failures. In this paper we demonstrate how online testing, as an active approach, can improve failure prediction by considering a broader range of service executions. Specifically, we introduce a framework and prototypical implementation that exploits synergies between monitoring, online testing and quality prediction. For online test selection and assessment we adapt usage-based testing strategies. We experimentally evaluate the strengths of our approach in predicting the need for an adaptation of an SBA.

A framework for designing and implementing the Ada standard container library

An open issue of the Ada language is the definition of a standard container library. Containers in this library (e.g., sets, maps and lists) shall offer some core functionalities that characterise their behaviour (i.e., different strategies for managing the elements stored therein) as well as other general functionalities. Among these general functionalities, we are interested in alternative ways for accessing the containers, namely direct access by position and traversals using iterators. In this paper, we present the Shortcut-Based Framework (SBF), a framework aimed at providing suitable, uniform, accurate and secure access by position and iterators, while keeping other nice properties such as comprehensibility and changeability. The SBF should be considered as a baseline upon which the Ada standard container library can be built. We assess the feasibility of our proposal defining a quality model for container libraries and evaluating the SBF using some metrics defined with the Goal-Question-Metric approach.

Quality models for web services: A systematic mapping

Context: Quality of Service (QoS) is a major issue in various web service related activities. Quality models have been proposed as the engineering artefact to provide a common framework of understanding for QoS, by defining the quality factors that apply to web service usage. Objective: The goal of this study is to evaluate the current state of the art of the proposed quality models for web services, specifically: (1) which are these proposals and how are they related; (2) what are their structural characteristics; (3) what quality factors are the most and least addressed; and (4) what are their most consolidated definitions. Method: We have conducted a systematic mapping by defining a robust protocol that combines automatic and manual searches from different sources. We used a rigorous method to elicitate the keywords from the research questions and a selection criteria to retrieve the final papers to evaluate. We have adopted the ISO/IEC 25010 standard to articulate our analysis. Results: We have evaluated 47 different quality models from 65 papers that fulfilled the selection criteria. By analyzing in depth these quality models, we have: (1) distributed the proposals along the time dimension and identified their relationships; (2) analyzed their size (visualizing the number of nodes and levels) and definition coverage (as indicator of quality of the proposals); (3) quantified the coverage of the different ISO/IEC 25010 quality factors by the proposals; (4) identified the quality factors that appeared in at least 30% of the surveyed proposals and provided the most consolidated definitions for them. Conclusions: We believe that this panoramic view on the anatomy of the quality models for web services may be a good reference for prospective researchers and practitioners in the field and especially may help avoiding the definition of new proposals that do not align with current research.

Enhancing Federated Cloud Management with an Integrated Service Monitoring Approach

Cloud Computing enables the construction and the provisioning of virtualized service-based applications in a simple and cost effective outsourcing to dynamic service environments. Cloud Federations envisage a distributed, heterogeneous environment consisting of various cloud infrastructures by aggregating different IaaS provider capabilities coming from both the commercial and the academic area. In this paper, we introduce a federated cloud management solution that operates the federation through utilizing cloud-brokers for various IaaS providers. In order to enable an enhanced provider selection and inter-cloud service executions, an integrated monitoring approach is proposed which is capable of measuring the availability and reliability of the provisioned services in different providers. To this end, a minimal metric monitoring service has been designed and used together with a service monitoring solution to measure cloud performance. The transparent and cost effective operation on commercial clouds and the capability to simultaneously monitor both private and public clouds were the major design goals of this integrated cloud monitoring approach. Finally, the evaluation of our proposed solution is presented on different private IaaS systems participating in federations.

Integrated Monitoring Approach for Seamless Service Provisioning in Federated Clouds

Cloud Computing offers simple and cost effective outsourcing in dynamic service environments, and allows the construction of service-based applications using virtualization. By aggregating the capabilities of various IaaS cloud providers, federated clouds can be built. Managing such a distributed, heterogeneous environment requires sophisticated interoperation of adaptive coordinating components. In this paper we introduce an integrated federated management and monitoring approach that enables autonomous service provisioning in federated clouds. In this architecture, cloud brokers manage the number and the location of the utilized virtual machines for the received service requests. In order to provide seamless service executions, a state of the art monitoring solution is proposed that supports cloud selection performed by the management layer of the architecture. Our solution is able to cope with highly dynamic service executions by federating heterogeneous cloud infrastructures in a transparent and autonomous manner.

SALMonADA: a platform for monitoring and explaining violations of WS-agreement-compliant documents

Quality assurance techniques have been developed to supervise the service quality (QoS) agreed between service-based systems (SBSs) consumers and providers. Such QoS is usually included in service level agreements (SLAs) and thus, SLA monitoring platforms have been developed supporting violation detection. However, just a few of them provide explanation of the violations caused by observed QoS at monitoring time, but not in an user-friendly format. Therefore, we propose a general monitoring and analysis conceptual reference model and we instantiated it with SALMonADA, a SBS that notifies the clients with violations and their causes in their own easy-to-understand specification terms. In addition, our platform performs an early analysis notification that avoids delays in the client notification time when a violation takes place. Moreover, we have implemented a web application as a SALMonADA client, to prove how it monitors, analyses and reports to their clients the service level fulfillment of real services subject to a SLA specified with WS-Agreement.

The Crowd in Requirements Engineering: The Landscape and Challenges

Crowd-based requirements engineering (CrowdRE) could significantly change RE. Performing RE activities such as elicitation with the crowd of stakeholders turns RE into a participatory effort, leads to more accurate requirements, and ultimately boosts software quality. Although any stakeholder in the crowd can contribute, CrowdRE emphasizes one stakeholder group whose role is often trivialized: users. CrowdRE empowers the management of requirements, such as their prioritization and segmentation, in a dynamic, evolved style through collecting and harnessing a continuous flow of user feedback and monitoring data on the usage context. To analyze the large amount of data obtained from the crowd, automated approaches are key. This article presents current research topics in CrowdRE; discusses the benefits, challenges, and lessons learned from projects and experiments; and assesses how to apply the methods and tools in industrial contexts. This article is part of a special issue on Crowdsourcing for Software Engineering.

Making explicit some implicit i * language decisions

The i* (i-star) framework is one of the most widely adopted modelling approaches by several communities (business modelling, requirements engineering, ...). Probably due to its highly strategic nature, the definition of the modelling language offered by the framework does not make explicit the full behaviour of some basic constructs, leaving them thus open to several interpretations. This looseness may not be important in some contexts, even it may be beneficial since it leaves room for researchers to customize the framework to their needs. However, it becomes an obstacle in other situations, e.g., model interoperability and model-driven development. In this paper we identify ambiguities and silences in the i* language definition in a systematic manner, and then we propose an interpretation to deal with them. In some cases, the proposal may include the addition of some annotation into some language construct. The result is a formal definition taking the form of a UML conceptual data diagram (a metamodel) with several important integrity constraints.

Goal-Driven Adaptation of Service-Based Systems from Runtime Monitoring Data

Service-based systems need to provide flexibility to adapt both to evolving requirements from multiple, often conflicting, ephemeral and unknown stakeholders, as well as to changes in the runtime behavior of their component services. Goal-oriented models allow representing the requirements of the system whilst keeping information about alternatives. We present the MAESoS approach which uses i* diagrams to identify quality of service requirements over services. The alternatives are extracted and kept in a variability model. A monitoring infrastructure identifies changes in runtime behavior that can propagate up to the level of stakeholder goals and trigger the required adaptations. We illustrate the approach with a scenario of use.

Using Normalized Compression Distance for image similarity measurement: an experimental study

Similarity metrics are widely used in computer graphics. In this paper, we will concentrate on a new, algorithmic complexity-based metric called Normalized Compression Distance. It is a universal distance used to compare strings. This measure has also been used in computer graphics for image registration or viewpoint selection. However, there is no previous study on how the measure should be used: which compressor and image format are the most suitable. This paper presents a practical study of the Normalized Compression Distance (NCD) applied to color images. The questions we try to answer are: Is NCD a suitable metric for image comparison? How robust is it to rotation, translation, and scaling? Which are the most adequate image formats and compression algorithms? The results of our study show that NCD can be used to address some of the selected image comparison problems, but care must be taken on the compressor and image format selected.