Efficiently synchronizing data with external sources, such as social media feeds, while minimizing well-timed requests is a challenge in various domains. This research investigates prediction algorithms for determining appropriate update intervals for Facebook and Twitter feeds, considering metrics such as the delay (time between a post's publication and retrieval) and requests per post. Due to variations in update intervals, different algorithms yield diverse results. Selecting the most suitable algorithm for each feed is a time-consuming but crucial task for achieving optimal resource usage. We propose three strategies for algorithm selection: baseline (using a single algorithm per feed), optimum (calculating the best algorithm for each feed), and classification (identifying algorithms through classification). Real-world data from Facebook and Twitter are used to evaluate the strategies, comprehensively assessing their strengths and weaknesses. Findings demonstrate that the strategy optimum identifies the best algorithms, while the strategy classification selects fairly good algorithms at significantly reduced computational effort.

The synchronization of data against external sources with as few well-timed requests as possible is a challenge in several domains, that also applies to online social networks (OSNs). This paper examines algorithms that can be used to predict appropriate update intervals for feeds on Facebook and Twitter. The metrics to be optimized are the delay, meaning the time between publication and retrieval of the posts, as well as the requests per post. The approaches examined include static and adaptive algorithms as well as Poisson processes. The different strategies are first described, then applied to real-world data from Facebook and Twitter to finally compare and discuss the measurements. The various algorithms have different strengths and weaknesses. Hence, we show that with Poisson processes, the most fitting update intervals can be found, which keep both the post delay and the number of requests in a good ratio.

Learning in universities can be characterised as self-regulated learning [1]: students have to set learning goals, apply learning strategies, assess their progress, correct their strategies and redefine goals in cyclic phases. IT-based educational tools enhance lectures and provide numerous opportunities to support students in mastering the demands of self-regulated learning (e.g., by providing quizzes). The data basis of such tools can be utilised in order to support students during the phases of (self-)assessment and correction. Additionally, teachers can benefit from fine-grained analysis of individual lectures and assessments of the student group's conduct in order to improve their lectures. Both, teachers and students directly benefit from structured feedback on individual as well as group performance. However, the information required for beneficiary feedback to students and teachers must be presented in an ordered and well-prepared fashion. Evaluation centres can offer an automated extraction of important information based on the underlying data stored by the IT-based educational tools. In this short position paper we present a prototypical evaluation centre and discuss how it can assist teachers in improving their lectures, while it provides students with required information for correct self-assessment at the same time. The proposed evaluation centre was tested in different settings and preliminary results based on subjective user feedback can be extracted.

Data centres and similar server clusters consume a large amount of energy. However, not all consumed energy produces useful work. Servers consume a disproportional amount of energy when they are idle, underutilised, or overloaded. The effect of these conditions can be minimised by attempting to balance the demand for and the supply of resources through a careful prediction of future workloads and their efficient consolidation. In this paper we extend the cutting stock problem for consolidating workloads having stochastic characteristics. Hence, we employ the aggregate probability density function of co-located and simultaneously executing services to establish valid patterns. A valid pattern is one yielding an overall resource utilisation below a set threshold. We tested the scope and usefulness of our approach on a 16-core server with 29 different benchmarks. The workloads of these benchmarks have been generated based on the CPU utilisation traces of 100 real-world virtual machines which we obtained from a Google data centre hosting more than 32000 virtual machines. Altogether, we considered 600 different consolidation scenarios during our experiment. We compared the performance of our approach-system overload probability, job completion time, and energy consumption-with four existing/proposed scheduling strategies. In each category, our approach incurred a modest penalty with respect to the best performing approach in that category, but overall resulted in a remarkable performance clearly demonstrating its capacity to achieve the best trade-off between resource consumption and performance.

University courses in STEM fields benefit tremendously from the introduction of IT-based education tools (IET). Learning is not limited to knowledge of, but extended to knowledge acquisition through IET utilization. With the introduction of IETs, the preparation of lectures and courses becomes increasingly challenging for lecturers. Lecturers must know the IET's functional range and the didactical concept underlying each. They must also consider the interaction of IETs among each other and their behavior under different circumstances (time in semester, audience size, etc.). Additionally, didactics preferences of lecturers gravely influence IET selection. Only few solutions exist with an approach utilizing guided selection of IETs; none of which offers comprehensive explanations of didactics concepts and influencing factors. Attempting to address these problems, we added a guided IET selection to our AMCS platform which includes nine IETs not suitable for utilization at the same time. Our guided IET selection addresses didactical design as well as feasible und suitable combinations of the IETs. Any suggestion to lecturers at lecture or course creation time bases on a simple algorithm, which takes all of the before-mentioned aspects into consideration, while at the same time providing useful hints and explanations to the lecturers.

The architectures of large-scale Internet servers are becoming more complex each year in order to store and process a large amount of Internet data (Big Data) as efficiently as possible. One of the consequences of this continually growing complexity is that individual servers consume a significant amount of data even when they are idle. In this paper we experimentally investigate the scope and usefulness of existing and proposed dynamic power management strategies to manage power at core, socket, and server levels. Our experiment involves four dynamic voltage and frequency scaling policies, three different workloads having different resource consumption statistics, and the activation and deactivation of different sockets (packets) of a multicore, multi-socket server. Moreover, we establish a quantitative relationships between the workload (w) and the estimated power consumption (p) under different power management strategies to make a quantitative comparison of the different strategies and server configurations.

This paper presents the results of an empirical experiment conducted in an academic environment with the aim of comparing the specification of acceptance test cases with executable and nonexecutable test description formats in the domain of event processing application development. In the experiment subjects had to specify functional test cases for given requirements. We evaluated the effort, test coverage and perceived difficulty. Our results show a positive effect on using the executable test description with regard to the effort of test specification.

Acceptance test driven development is a promising method to support agile software development. It is aiming to improve development efficiency by automation of test execution and detailed communication of domain knowledge. In this paper a systematic literature review in the field of acceptance test driven development is reported, with the aim of studying existing knowledge and observations in this area. Our search strategy resulted in finding 26 research studies, with 14 experiment papers and 12 use cases papers. We investigated the studies according to a predefined data extraction form. The review investigates the findings of identified empirical research studies. The results are categorized and discussed within the context of previous related reviews.

Teaching in classic courses offers too little interaction between docents and students and should be improved. Addressed approaches include a range from Simple Voting Systems to Clickers and Audience Response Systems, and interaction and Student motivation may be improved therein. However, different university course settings are affected in different ways by these systems. Therefore, this paper presents a comparison of a selected range of these systems (implemented as tool kits) within two course settings, namely lecture readings and exercise tutorials. These tools are Audience Response Systems, Question and Answer Systems (Q&A Systems), Discussion Systems (Panels), as well as Virtual Whiteboard Feedback Systems. A synopsis of feasibility for different settings is provided and concluded with important results on the distinguishability of Q&A Systems and Panels.

In this paper, we present an empirical study that conducts the impact of Rated Tags on customers' decision making process in online stores. A Rated Tag is a combination of a user-generated tag and a 5-star rating scale. The Rated Tags system aims to support consumers' decisions and therefore falls into the category of interactive decision aids. The questions answered in this paper are whether Rated Tags can increase the decision making quality and decrease the decision effort of consumers. For this purpose, we have extracted 100 real customer reviews from amazon.de, which were assigned Rated Tags. The customer reviews and Rated Tags were used as a basis for the decision making process of our participants. The results of the study are promising. Participants of the Rated Tags group had an increased decision quality and a decreased decision making effort compared to the participants of the control group.

The cloud computing paradigm is one of the most promising of its kind. The demand and supply of online delivered software have been continuously growing. However, reports have shown that various Software as a service solutions have not succeeded in reaching cloud user expectations. Hence, users need to be satisfied with the service quality which is determined by the fulfillment of both functional and non-functional requirements. Currently, the evaluation of the cloud service quality consider-ing individual requirements is up to the user. Unfortunately, the amount of non-functional quality criteria is very high and some are laborious to determine. We believe that an information system could support and enable users without specific knowledge to evaluate comprehensively and rapidly the quality of their cloud. In this paper we first present a quality model for SaaS. In addition, we demonstrate how the quality information should be structured and visualized in a user-friendly way. With the provided transparency users are able to establish quality awareness in the long term.

Workload consolidation is one of the common approaches applied to achieve energy efficiency in data centres. It allows to reduce the number of physical machines needed to run the applications and thus, save energy. Workload consolidation can be realized via live migration of virtual machines (VMs) from one server to another with the aim to power off idle machines. In spite of innumerable benefits, the VM migration process introduces additional costs to the system in terms of migration time, during which the quality of provided services may be declined, and the energy overhead. The migration time depends on the applications that run on the VMs. The VMs which run simultaneously on the physical machine compete for the available resources, and thus, the interference effects that occur, influence the migration time. This paper investigates into the influence of workload as well as interference effects on the migration time of multiple VMs. In our experiments we utilize benchmarks from the SPEC CPU2006 benchmark suite and use Kernel-based Virtual Machine (KVM) as a hypervisor. We show experimentally that interference effects occur and affect the migration time of VMs. We migrate multiple VMs in all possible combinations and investigate into the migration times.

Even though classical lectures at universities are criticized for lacking interactivity and treating students like passive receptors of information they are still very popular. Due to the big amount of students, interaction between teacher and students is difficult to realize. Several projects address this problem by offering technical solutions which aim at increasing the interactivity during classes or lectures â?? classic clicker-systems as well as solutions in which students use their own smartphones, netbooks or tablet-PCs. Based on research on self-regulated learning (SRL) processes we developed the already existing tools one step further: instead of only providing questions we designed Auditorium Mobile Classroom Service (AMCS) â?? a program which offers several possibilities to interact during a lecture. AMCS supports students to regulate their own learning process during the lecture. Learning questions are one core element to support them. On the basis of the results of the learning questions specific advices and hints are sent to the studentsâ?? smartphones or notebooks. The features increase the interactivity between the content and students and the interaction in the lecture hall. In the present article the program AMCS is described. Furthermore we report first experiences from a field test in a university lecture.

We introduce and demonstrate NubiVis, a web-based tool for exploring and managing personal files stored in arbitrary locations with a unified view. NubiVis supports views on files partitioned and dispersed across several storage services when running atop the NubiSave cloud storage controller, as we

The power consumption of presently available Internet servers and data centers is not proportional to the work they accomplish. The scientific community is attempting to address this problem in a number of ways, for example, by employing dynamic voltage and frequency scaling, selectively switching off idle or underutilized servers, and employing energy-aware task scheduling. Central to these approaches is the accurate estimation of the power consumption of the various subsystems of a server, particularly, the processor. We distinguish between power consumption measurement techniques and power consumption estimation models. The techniques refer to the art of instrumenting a system to measure its actual power consumption whereas the estimation models deal with indirect evidences (such as information pertaining to CPU utilization or events captured by hardware performance counters) to reason about the power consumption of a system under consideration. The paper provides a comprehensive survey of existing or proposed approaches to estimate the power consumption of single-core as well as multicore processors, virtual machines, and an entire server.

Testing distributed systems is difficult, error-prone and time-consuming. Especially scalability tests are hard to perform because of the large number of connected devices. The heterogeneity of these devices (PCs, smart phones, tablets) and their various network access technologies (DSL, cable, WiFi, 3G/4G) even worsen the situation. We argue that the reproduction of network conditions is necessary to provide an adequate test bed for experiments with distributed systems. We therefore propose an architecture that allows performing automated tests of large scale distributed systems including the emulation of network and application behavior.

Distributed data storage is a topic of growing importance due to the mounting pressure to find the right balance between capacity, cost, privacy and other non-functional properties. Compared to central storage on physical media, on the network or in a cloud storage service, advanced data distribution techniques offer additional safety, security and performance. On the downside, these advantages come with a much higher complexity regarding the choice and configuration of where to store which parts of the data, and subsequent verification of where which data had been stored. Often, the storage targets must be configured individually while a centrally and locally accessible configuration interface with an appropriate propagation and verification mechanism would be more suitable. The complexity is further increased by additional data pre-processing tasks which are selectively applied to some of the targets. Compression, encryption and deduplication are typically present in pre-processing. With Storage Flows, we propose a new concept to manage distributed storage flows through systematic orchestration. The flows connect clients flexibly with intermediate data pre-processing tasks and finally the storage targets. We show that Storage Flows can be formalised and demonstrate their practical usefulness with implemented configuration and verification tools.

Automatic information extraction from scanned business documents is especially valuable in the application domain of document archiving. But current systems for automated document processing still require a lot of configuration work that can only be done by experienced users or administrators. We present an approach for information extraction which purely builds on end-user provided training examples and intentionally omits efficient known extraction techniques like rule based extraction that require intense training and/or information extraction expertise. Our evaluation on a large corpus of business documents shows competitive results of above 85% F1-measure on 10 commonly used fields like document type, sender, receiver and date. The system is deployed and used inside the commercial document management system DocuWare.

Virtualization and broadband Internet connections enabled existing technologies to form up under the nebulous term cloud. Cloud computing promises near infinite scalability and cost reduction by pay per use agreements. However for data outsourced to existing cloud solutions - which can be considered synonymous with unknown locations and potentially hostile environments - the security protection objectives can not be guaranteed. We present an approach that enables users to benefit from cloud computing and retain data sovereignty.

Most Internet applications employ some kind of load balancing policies in a cluster setting to achieve reliable service provision as well as to deal with a resource bottleneck. However, these policies may not ensure the utilization of \textit{all} of the hardware resources in a server equally efficiently. This paper experimentally investigates the relationship between the power consumption and resource utilization of a multimedia server cluster when different load balancing policies are used to distribute a workload. Our observations are the following: (1) A bottleneck on a single hardware resource can lead to a significant amount of underutilization of the entire system. (2) A ten times increment in the network bandwidth of the entire cluster can double the throughput of individual servers. The associated increment in power consumption of the individual servers is 1.2% only. (3) For TCP-based applications, session information is more useful than other types of status information to utilize power more efficiently. (4) The use of dynamic frequency scaling does not affect the overall throughput of IO-bound applications but reduces the power consumption of the servers; but this reduction is only 12% of the overall power consumption. More power can be saved by avoiding a resource bottleneck or through service consolidation.

Web feeds allow users to retrieve new content from pages on the World Wide Web. Feeds are offered by a multitude of web pages, ranging from conventional news sites to pages with user generated content such as wikis, forums or personal blogs. They notify interested readers of new content and are therefore interesting for information retrieval tasks. Unfortunately, there is no comprehensive dataset of feeds publicly available, making it difficult for researchers to work with this kind of data and, more importantly, to compare their research results by using a common dataset.

In federated information systems, deciding whether an information source is relevant for a given query is crucial for its overall performance. Focusing on uncooperative unstructured information sources, we analyze several drawbacks of the popular CORI resource selection algorithm by evaluating it in a federated product information scenario. Based on these results, we propose and describe a novel approach using an ontology-based sampling method, which is used to initialize an Explicit Semantic Analysis index.

The energy consumption of ICT infrastructures has increased considerably in the recent years. This has resulted in extensive research on dynamic power management strategies as well as data centre design and placement. The main problem with most of the proposed or existing approaches is that they do not fully take the distributed nature of and strong logical dependencies between executed services into account. However, without a comprehensive knowledge of the wider relationships between services, local power management strategies may be ineffectual or can even result in high aggregate energy cost. Understanding this relationship is useful for fine-grained energy-aware computing. For example, services that run on underutilised servers can be stopped or seamlessly migrated to other servers, so that the underutilised servers can be turned off. Alternatively, a re-binding process can be used if the cost of service migration is high. Such advantages can be fully exploited if the dependency between services is properly understood and meaningfully modelled. This paper introduces a conceptual architecture for an energy-aware service execution platform and compares three optimisation mechanisms to support dynamic service migration and rebinding.

This paper investigates the energy cost of control packets in contention-based medium access control protocols in wireless sensor networks. Control packets are useful to avoid collision and overhearing, but cost a significant amount of energy. Therefore, whether or not to apply control packets is a trade-off. It will be shown that this trade-off mainly depends on the packet arrival rate at individual nodes, the transmission rate, the duty cycle and the average number of active neighbors in the network.

The service-oriented approach with his essential advantages of a uniform interface and the possibility to reuse distributed and heterogeneous services in other contexts has led to a high popularity in Business-to-Business (B2B) scenarios. However, the development of user interfaces (UI) lacks of comparable efforts for the Business-to-Consumer (B2C) interaction because B2C is not properly reflected in current service technology standards. We address this issue with a pragmatic matching approach to support the discovery of UI components and the provision of suggestions that can be exploited for the development of user interfaces for service-based applications. The matching relies entirely on functional descriptions because semantic descriptions play a minor role in practice and almost all available Web services are described by their functional interface focusing on operations, parameters and data types.

Service level agreements (SLAs) are used to manifest guarantees about certain functional and non-functional aspects of service execution. Service providers are confronted with a hard problem when trying to estimate reasonable QoS levels and other default settings for SLA templates. The insufficient use of formal service behavior descriptions, varying resource demands and a choice of configuration options expected by users contribute to this issue. We present our solution of gathering monitoring data at runtime and feeding it back into the service registry to adjust descriptions and make contract template derivation a more realistic process. In addition, we show how to extend SOA building blocks such as service discoveries and SLA managers with the adjustment mechanism.

The growing demand for a wireless link is taking the deployment of wireless local area networks away from the notion of carefully planned and carefully managed setting, into a randomly deployed and independently managed (if at all) network setting. This results in highly contentious networks. In fact research shows that in most metropolitan cities, the size of contentious access points that are closely located with each other are overwhelmingly high. Subsequently, the performance of these networks is highly fluctuating and unpredictable. This paper aims to show how spontaneously deployed networks perform in the presence of fluctuating node densities. We perform an exhaustive simulation for different applications, including, VoIP, HTTP, and FTP. We focus on non-commercial deployments (private use at home or in an apartment).

The idea of the future internet of services is to combine several services of numerous service providers to new value-added services or applications. To sell these services on so-called service marketplaces the providers have to ensure a high quality of service execution. But how could a provider of a composed service ensure the quality of the whole application, if single services of other providers fail or do not reach the required level of quality? This article describes an approach for modeling adaptation in web service compositions to ensure a guaranteed quality of service for the whole composite service. A special adaptation mechanism is the rebinding of single services while the process is executed if the services fail or could not reach the needed QoS level. We will present a solution for modeling these rebinding concepts in BPEL processes and the infrastructure to support this adaptation mechanism at run-time.

For quite some time now, applications have been designed and developed in various projects of our research group by using middleware. In addition, various middleware products have been evaluated. An existing client/server system has been converted to EJB. The subject of this paper will be the results of these studies, along with the characteristics of the analyzed servers other concepts and related work.

Recently there has been increasing interest in the application of broadcast networks as high-bandwidth downstream channels of hybrid asymmetric communication platforms. This interest stems from an increasing number of mobile internet users demanding for high quality services, whereas wireless networks still lack in bandwidth substantially.

There is a growing set of UDP (user datagram protocol) based applications using inadequate congestion control algorithms or none at all (i.e., the flow does not throttle back upon receipt of congestion notification). Such UDP applications include streaming applications like packet voice and video, and also multicast bulk data transfer. Congestion avoidance algorithms in routers are not able to handle these flows adequately and this leads to an unfair distribution of bandwidth among TCP and UDP flows in times of congestion. Moreover the random dropping of IP packets in times of congestion in routers causes a decreasing goodput delivered to the receiving application because whole TCP or UDP packets are discarded at the receiver when one IP packet is missed. This leads to retransmissions when using TCP and can cause serious problems with the display of a multimedia stream when using UDP. This paper proposes a method to overcome the mentioned problems by introducing an additional header into the IPv6-header (Internet Protocol Version 6 Draft Specification, 1998) to label the dependencies of several IP packets and distinguish between different flows at the IP level. A structured description of the application data contents helps to include dependencies of the application data level. The description is mapped onto several priority levels to describe the dependencies within an ADU (application data unit). This paper also explains the way to derive ADUs from the multimedia data and the benefit that can be taken from IP-labeling inside the Internet. As a technical basis, the concepts described in the paper are validated by a simulation study.

Distributed applications are of growing importance in many application fields such as office automation, manufacturing, telematics or information services. This paper outlines support facilities for such applications based on distributed platforms. It then discusses further requirements resulting from the use of advanced network technologies. Architectural support for such environments is presented and experiences with specific software support solutions are discussed. As an application example, workflow processing in distributed environments is used in order to illustrate the approaches. The paper concludes with an outlook to future work.

Resource reservation in advance (ReRA) enables scheduling and allocation of resources at an early stage in time. This way, the availability of resources can actually be guaranteed for the point in time when the resources are needed. As opposed to that, current reservation protocols such as RSVP perform an "immediate" reservation without advance scheduling. They can therefore suffer shortage of resources with subsequent rejection of applications. This paper describes our new approach for providing resource reservation in advance in ATM networks. As a foundation, we first present experiences of IPng and RSVP over ATM. Based on this work, we then discuss major design issues of an appropriate ReRA solution. Important aspects are the signalling model for ReRA, the admission control strategy, the duration of connections, and various other time-related parameters. We also discuss our ongoing implementation of ReRA as an extension of RSVP and outline directions for future research in this area.

Describes a new workflow management system (WfMS) named CodAlf ("Code-name Alfa"). It is based on a completely decentralized system architecture. The approach especially enables the support of distributed organizations as well as dynamic growth and reconfiguration. CodAlf supports collaborative work and decentralization with the help of a comfortable type management. The implementation uses the OSF Distributed Computing Environment (DCE) as a basis. All components are modeled and implemented as objects of a distributed system on top of DC++, an object-oriented extension of DCE. In addition to runtime support, a workflow specification language and a workflow design tool are offered. The system is also compared to commercially-available WfMSs and to decentralized object-oriented approaches.

No abstract available.

Complex distributed office procedures are based on sequential and parallel execution of basic services offered by a distributed service environment. Office procedure execution can be considered to be a special kind of group communication with groups of collaborating servers. This paper first presents a general group communication abstraction. We then show in detail how the generic approach has been extended and specialized in order to support complex office procedures. The extended solution comprises a graph-based, declarative specification notation for office procedures, and a distributed runtime support environment. This maps office procedure service requests dynamically to actual servers for execution. Moreover, additional management facilities enable external supervision of office procedures. Based on examples, we show how applications can benefit from the abstractions. By discussing their similarities and evolution, we also outline the strong relationship between group communication and office procedures.