Managing the complex data center environment: an Integrated Energy-aware Framework

The problem of Information Technology energy consumption has gained much attention due to the always increasing use of IT both for business and for personal reasons. In particular, data centers are now playing a much more important role in the modern society, where the information is available all the time and everywhere. In this context, the aim of this paper is to study energy efficiency issues within data centers from the Information System perspective. The proposed approach integrates the application and infrastructure capabilities, in which the enactment of adaptation mechanisms is aligned with the business process. Based on both energy and quality dimensions of service-based applications, a model-based approach supports the formulation of new constrained optimization problem that takes into consideration over-constrained solutions where the goal is to obtain the better trade-off between energy and quality requirements. These ideas are combined within a framework where time-based analysis allow the identification of potential system threats and drive the selection of adaptation actions improving overall energy and quality requirements, represented by indicators satisfaction. In addition, the framework includes an evolution mechanism that is able to evaluate past decisions feedback in order to adjust the model according to the current underlying environment. Finally, the benefits of the approach are analyzed in an experimental setting

An Investigation into Dynamic Web Service Composition Using a Simulation Framework

[Motivation] Web Services technology has emerged as a promising solution for creat- ing distributed systems with the potential to overcome the limitation of former distrib- uted system technologies. Web services provide a platform-independent framework that enables companies to run their business services over the internet. Therefore, many techniques and tools are being developed to create business to business/business to customer applications. In particular, researchers are exploring ways to build new services from existing services by dynamically composing services from a range of resources. [Aim] This thesis aims to identify the technologies and strategies cur- rently being explored for organising the dynamic composition of Web services, and to determine how extensively each of these has been demonstrated and assessed. In addition, the thesis will study the matchmaking and selection processes which are essential processes for Web service composition. [Research Method] We under- took a mapping study of empirical papers that had been published over the period 2000 to 2009. The aim of the mapping study was to identify the technologies and strategies currently being explored for organising the composition of Web services, and to determine how extensively each of these has been demonstrated and assessed. We then built a simulation framework to carry out some experiments on composition strategies. The rst experiment compared the results of a close replication of an ex- isting study with the original results in order to evaluate our close replication study. The simulation framework was then used to investigate the use of a QoS model for supporting the selection process, comparing this with the ranking technique in terms of their performance. [Results] The mapping study found 1172 papers that matched our search terms, from which 94 were classied as providing practical demonstration of ideas related to dynamic composition. We have analysed 68 of these in more detail. Only 29 provided a `formal' empirical evaluation. From these, we selected a `baseline' study to test our simulation model. Running the experiments using simulated data- sets have shown that in the rst experiment the results of the close replication study and the original study were similar in terms of their prole. In the second experiment, the results demonstrated that the QoS model was better than the ranking mechanism in terms of selecting a composite plan that has highest quality score. [Conclusions] No one approach to service composition seemed to meet all needs, but a number has been investigated more. The similarity between the results of the close replication and the original study showed the validity of our simulation framework and a proof that the results of the original study can be replicated. Using the simulation it was demonstrated that the performance of the QoS model was better than the ranking mechanism in terms of the overall quality for a selected plan. The overall objectives of this research are to develop a generic life-cycle model for Web service composition from a mapping study of the literature. This was then used to run simulations to replicate studies on matchmaking and compare selection methods

Verification of communication protocols in web-services

The last decade has seen a massive migration towards the service oriented paradigm that has resulted in 1) resolving the software interoperability issues, 2) increased re-usability of the code, 3) easy inter-application communications, and 4) significant cost reduction. However, individual web-services seldom meet the business requirements of an application. Usually an application life-cycle involves interacting with several web-services based on its workflow. Considering that this might require 1) sharing data with multiple services, 2) tracking the response for each service request, 3) tracking and compensating the service failures, etc., usually a domain-specific language is used for service composition. Each service has an interface to outline its functionality and they are composed based on these interfaces. Nevertheless, any error or omission in these exposed interfaces could result in a myriad of glitches in the composition and the overlying application. This is further exacerbated by dynamic service composition techniques wherein services could be added, removed or updated at runtime. Consequently service consuming applications heavily depend on the verification techniques to vouch for their reliability and usability. The scope of applications based on service composition is rapidly expanding into critical domains where the stakes are high (e.g. stock markets). Consequently their reliability cannot be solely based on testing, wherein educated guesses are involved. Model-checking is a formal method that has an unprecedented ability to endorse the correctness of a system. It involves modeling a system before verifying it for a set of properties using a model-checking tool. However it has hitherto been sparingly used because of the associated time and memory requirements. This thesis proposes novel solutions to deal with these limitations in verifying a service composition. We propose a technique for modeling a service composition prior to verifying it using a model-checking tool. Compared to existing techniques that are ad-hoc and temporary, our solution streamlines the transformation by introducing a generic framework that transforms the composition into intermediate data transfer objects (DTOs) before the actual modeling. These DTOs help in automating the transformation by allowing access to the required information programmatically. The experimental results indicate that the framework takes less than a second (on average) in transforming BPEL specifications. The solution is made more appealing by further reducing the aforementioned time and memory requirements for model-checking. The additional reduction in memory is attributed to storing the states as the difference from an adjoining state. The reduction in time is realized by exploring the modules of a hierarchical model concurrently. These techniques offer up to 95% reduction in memory requirements and 86% reduction in time requirements. Furthermore, the time reduction technique is also extended to non-hierarchical models. This involves introducing hierarchy into a flat model in linear time before applying the time reduction techniques. As compared to other techniques, our method ensures that the transformed model is equivalent to the original model