Abstract In this paper, we investigate how to improve the profits in cloud infrastructures by using price schemes and analyzing the user interactions with the cloud provider. For this purpose, we consider two different types of client behavior, namely regular and high-priority users. Regular users do not require a continuous service, and they can wait to be attended to. In contrast, high-priority users require a continuous service, e.g., a 24/7 service, and usually need an immediate answer to any request. A complete framework has been implemented, which includes a UML profile that allows us to define specific cloud scenarios and the automatic transformations to produce the code for the cloud simulations in the Simcan2Cloud simulator. The engine of Simcan2Cloud has also been modified by adding specific SLAs and price schemes. Finally, we present a thorough experimental study to analyze the performance results obtained from the simulations, thus making it possible to draw conclusions about how to improve the cloud profit for the cloud studied by adjusting the different parameters and resource configuration.

In this paper, we model cloud systems and the user interactions with the cloud provider using the UML2Cloud profile.In general, users request virtual machines according to their needs, but they can also subscribe to the cloud provider and wait to be notified when the requested resources are not available.In this case, users indicate a maximum subscription time, so once this time elapses without being notified, users leave the system unattended.In this paper, then, we present an exhaustive research study to measure how the user subscription times affect the overall system responsiveness.In this study, three different cloud configurations are analyzed.Each cloud processes several workloads, which are generated using two distribution functions for the user arrivals, namely a normal and a cyclic normal distribution.The purpose of this study is to find out the inflection point for the waiting time of the users, from which the cloud responsiveness and its performance do not improve.The obtained information is therefore useful for the cloud provider to improve the configuration of the cloud.

Cloud providers face the challenge of managing large amounts of heterogeneous resources in real time. It is usually very costly to conduct experiments with real cloud systems. Therefore, tools to analyze and evaluate cloud scenarios and experimental studies are very useful for them. In this paper, we model cloud systems and the user interactions with the cloud provider using the UML2Cloud profile. In general, users request virtual machines according to their needs, but they can also subscribe to the cloud provider and wait to be notified when the requested resources are not available. In this case, users indicate a maximum subscription time, so once this time elapses without being notified, users leave the system unattended. Thus, we present an exhaustive experimental study to measure how the user subscription times affect the overall system responsiveness. To this end, four different cloud configurations are analyzed, and the workloads for these studies are produced by using three distribution functions for the user arrivals, namely, a uniform, a normal, and a cyclic normal distribution. Furthermore, we also analyze the cloud performance with a workload obtained from a real trace. The purpose of this study is to find out the inflection point for the waiting time of the users, from which the cloud responsiveness and its performance do not improve. The obtained information is, therefore, useful for the cloud provider to improve the configuration of the cloud.

Abstract Wireless technologies are continuously evolving, including features such as the extension to mid- and long-range communications and the support of an increasing number of devices. However, longer ranges increase the probability of suffering from hidden terminal issues. In the particular case of Wireless Local Area Networks (WLANs), the use of Quality of Service (QoS) mechanisms introduced in IEEE 802.11e compromises scalability, exacerbates the hidden node problem, and creates congestion as the number of users and the variety of services in the network grow. In this context, this paper presents a configurable Colored Petri Net (CPN) model for the IEEE 802.11e protocol with the aim of analyzing the QoS support in mid- and long-range WLANs The CPN model covers the behavior of the protocol in the presence of hidden nodes to examine the performance of the RTS/CTS exchange in scenarios where the QoS differentiation may involve massive collision chains and high delays. Our CPN model sets the basis for further exploring the performance of the various mechanisms defined by the IEEE 802.11 standard. We then use this CPN model to provide a comprehensive study of the effectiveness of this protocol by using the simulation and monitoring capabilities of CPN Tools.

UML sequence diagrams are used to graphically describe the message interactions between the objects participating in a certain scenario. Combined fragments extend the basic functionality of UML sequence diagrams with control structures, such as sequences, alternatives, iterations, or parallels. In this paper, we present a UML profile to annotate sequence diagrams with combined fragments to model timed Web services with distributed resources under the publish/subscribe paradigm. This profile is exploited to automatically obtain a representation of the system based on Colored Petri nets using a novel model-to-model (M2M) transformation. This M2M transformation has been specified using QVT and has been integrated in a new add-on extending a state-of-the-art UML modeling tool. Generated Petri nets can be immediately used in well-known Petri net software, such as CPN Tools, to analyze the system behavior. Hence, our model-to-model transformation tool allows for simulating the system and finding design errors in early stages of system development, which enables us to fix them at these early phases and thus potentially saving development costs.

Despite that many real-life contracts include time constraints, for instance explicitly specifying deadlines by when to perform actions, or for how long certain behaviour is prohibited, the literature formalising such notions is surprisingly sparse. Furthermore, one of the major challenges is that compliance is typically computed with respect to timed event traces with event timestamps assumed to be perfect. In this paper we present an approach for evaluating compliance under the effect of imperfect timing information, giving a semantics to analyse contract violation likelihood.

In this paper we present a Timed Automata model for the Publish/Subscribe paradigm in the context of Web Service Compositions with distributed resources, on the basis of an algebraic language inspired by the WSRF standard constructions. This framework allows a set of participants in a Web Service composition to interact with one another and also to manage a collection of distributed resources. The model includes operations for clients to publish, discover and subscribe to resources, so as to be notified when the resource property values fulfill certain conditions (topic-based subscription). Simulation and model-checking techniques can therefore be applied to the obtained network of timed automata, in order to check whether certain properties of interest are satisfied. A specific case study is finally presented to illustrate the model and the verification of the relevant properties on the obtained timed automata model.

C-O diagrams have been introduced as a means to have a more visual representation of normative texts and electronic contracts, where it is possible to represent the obligations, permissions and prohibitions of the different signatories, as well as the penalties resulting from non-fulfillment of their obligations and prohibitions. In such diagrams we are also able to represent absolute and relative timing constraints. In this paper we present a formal semantics for C-O diagrams based on timed automata extended with information regarding the satisfaction and violation of clauses in order to represent different deontic modalities. As a proof of concept, we apply our approach to two different case studies, where the method presented here has successfully identified problems in the specification.

Abstract The main objective of this paper is to present an approach to accomplish verification in the early design phases of a system, which allows us to make the system verification easier, specifically for those systems with timing restrictions. For this purpose we use RT‐UML sequence diagrams in the design phase and we translate these diagrams into timed automata for performing the verification by using model checking techniques. Specifically, we use the Object Management Group's UML Profile for Schedulability, Performance, and Time and from the specifications written using this profile we obtain the corresponding timed automata. The ‘RT‐UML Profile’ is used in conjunction with a very well‐known tool to perform validation and verification of the timing needs, namely, the UPPAAL tool, which is used to simulate and analyze the behaviour of real‐time dynamic systems described by timed automata. Copyright © 2009 John Wiley & Sons, Ltd.

In this work we explain how to perform the design and verification of a Web Services composition with time restrictions using the Web Services Translation tool, WST for short. We pay special attention to Web Services systems with timing restrictions. As illustration, we use a case study called “Form Generator Service”, a system that allows developers to manage a form repository by means of several Web Services. We show how to design this system and the verification of some properties on it, using a Timed Automata representation.

In this paper we show how we can use a classical UML diagram, the sequence diagram, for the description of business process behavior based on Web services with time constraints. More specifically, we see how these diagrams can capture the main elements of the Web services business process execution language (WS-BPEL), and then, how we can translate these diagrams into Web services business process execution language.