Kwei-Jay Lin

Service selection algorithms for Web services with end-to-end QoS constraints

Web services are new forms of Internet software that can be universally deployed and invoked using standard protocols. Services from different providers can be integrated into a composite service regardless of their locations, platforms, and/or execution speeds to implement complex business processes and transactions. In this paper, we study the end-to-end QoS issues of composite services by utilizing a QoS broker that is responsible for selecting and coordinating the individual service component. We design the service selection algorithms used by QoS brokers to construct the optimal composite service. The objective of the algorithms is to maximize the user-defined utility function value while meeting the end-to-end delay constraint. We propose two solution approaches to the service selection problem: the combinatorial approach, by modeling the problem as the Multiple Choice Knapsack Problem (MCKP), and the graph approach, by modeling the problem as the constrained shortest path problem in the graph theory. We study efficient solutions for each approach.

Reputation-Oriented Trustworthy Computing in E-Commerce Environments

The reputation-oriented trust issue is critical to e-commerce applications and has drawn much attention from both industry and the research community. Existing e-commerce systems have introduced trust management mechanisms that provide some rating information to customers. However, more comprehensive mechanisms should be provided to more precisely depict the trust level of sellers on potential transactions, and the relationship between interacting entities. Here, the authors review the reputation-based trust evaluation mechanisms in literature and outline some trust issues that are particularly important in e-commerce environments.

Accountability monitoring and reasoning in service-oriented architectures

Service-oriented architecture (SOA) provides a powerful paradigm to compose service processes using individual atomic services. When running a service process, SOA needs an efficient and effective mechanism to detect service delivery failures and to identify the individual service(s) that causes the problem. In this research, we study the model of accountability to detect, diagnose, and defuse the real cause of a problem when service errors (such as incorrect result or SLA violation) occur in a service process. Our approach leverages Bayesian networks to identify the most likely problematic services in a process and selectively inspect those services. An evidence channel selection algorithm is designed to specify which services in a service network should be monitored to achieve the best cost-efficiency. We model the channels selection as the classic facilities location problem. We also adopt a continuous knowledge learning process to manage the dynamic nature of SOA. The performance study shows that our proposed accountability mechanism is effective on identifying the root cause of problems and can achieve significant cost savings: with 50% of services’ outputs monitored as evidence, the comprehensive diagnosis correctness can reach 80% after only 20% of services are inspected.

Scheduling real-time systems with end-to-end timing constraints using the distributed pinwheel model

Real-time distributed applications have timing constraints on tasks running on several processors. To design real-time systems with end-to-end performance requirements, we need to have algorithms to schedule and to coordinate tasks on different processor nodes. An end-to-end scheduling approach based on the pinwheel scheduling model is presented for distributed real-time systems, We show how tasks on different nodes may be transformed to have periods consisting of only harmonic numbers. With harmonic periods, we can use a polynomial-time algorithm to find the start and finish times of each task on each node. Phase alignment algorithms are then applied to adjust the phases between schedules of neighboring nodes so that the overall end-to-end delay is minimized. Using the distributed pinwheel model, schedules on different nodes are synchronized to lessen the delays. For many real-time systems, this approach provides a predictable performance and a short end-to-end delay.

Trust management towards service-oriented applications

In service-oriented computing (SOC) environments, service clients interact with service providers for services or transactions. From the point view of service clients, the trust status of a service provider is a critical issue to consider, particularly when the service provider is unknown to them. Typically, the trust evaluation is based on the feedback on the service quality provided by service clients. In this paper, we first present a trust management framework that is event-driven and rule-based. In this framework, trust computation is based on formulae. But rules are defined to determine which formula to use and what arguments to use, according to the event occurred during the transaction or service. In addition, we propose some trust evaluation metrics and a formula for trust computation. The formula is designed to be adaptable to different application domains by setting suitable arguments. Particularly, the proposed model addresses the incremental characteristics of trust establishment process. Furthermore, we propose a fuzzy logic based approach for determining reputation ranks that particularly differentiates new service providers and old (long-existing) ones. This is further incentive to new service providers and penalize poor quality services from service providers. Finally, a set of empirical studies has been conducted to study the properties of the proposed approaches, and the method to control the trust changes in both trust increment and decrement cases. The proposed framework is adaptable for different domains and complex trust evaluation systems.

A Formal Service Contract Model for Accountable SaaS and Cloud Services

Enabled by Service-Oriented Architecture (SOA), recently Software as a Service (SaaS) and Cloud computing are gaining momentum in the industry. An open issue is how to ensure accountability in business services offered through Internet. Traditionally a contract is an effective legal means to uphold accountability in business transactions. In this paper, we propose a novel service contract model called OWL-SC for e-Services. Based on OWL-DL and SWRL, OWL-SC model can be used to disclose obligations of both e-Services consumer and e-Services provider. More importantly, the model allows service participants to monitor the service contract execution and keep track of obligation fulfillment for each party during service delivery. We also propose a graphical model SC-CPN based on Colored Petri-Nets (CPN) to formally model contract obligations and their interdependencies. SC-CPN can also be used to validate the correctness of obligations in OWL-SC through simulation and state space analysis. Finally, we use the Congo Book service as an example to illustrate how to use OWL-SC and SC-CPN to build a service contract model.

Efficient online schedulability tests for real-time systems

Many computer systems, such as those for open system environments or multimedia services, need an efficient schedulability test for online admission control of new jobs. Although various polynomial time schedulability tests have been proposed, they often fail to decide the schedulability of the system precisely when the system is heavily loaded. On the other hand, most precise schedulability tests proposed to date have a high complexity and may not be suitable for online tests. We present new efficient online schedulability tests for both the periodic process model [C. L. Liu et al., (1973)] and the multiframe process model [A. K. Mok et al., (1997)] in uniprocessor environments. The schedulability tests are shown to be more precise and efficient than any existing polynomial-time schedulability tests. Moreover, the tests can be done incrementally as each new task arrives at the system. Our proposed tests can also be used for the multiframe model where a task may have different computation times in different periods. We show the performance of the proposed schedulability tests in several simulation experiments.

EGPS: a class of real-time scheduling algorithms based on processor sharing

A class of real time scheduling algorithms EGPS is proposed. Using EGPS, the schedulability of each process is enforced by a guaranteed CPU service rate, independent of the demands of other processes. Our research uses a GPS based framework for periodic and sporadic process scheduling, jitter control, service rate adjustment, and mixed scheduling of soft and hard real time processes. We then study the performance of the proposed algorithms by using a generic avionics platform example for our simulation experiments in jitter control and mixed scheduling of soft and hard real time processes.

An open real-time environment for parallel and distributed systems

Most computer-based systems have hard real-time constraints. Schedulers in complex systems must be designed to manage a set of applications developed and deployed independently. We study an open real-time environment architecture for distributed systems where real-time applications may run concurrently with non-real-time applications. The architecture uses a two-level scheduling scheme. Each application is assigned a sporadic server to schedule the processes in the application. All sporadic servers are then scheduled by a system-wide fixed priority scheduler. Using the proposed open environment architecture, all hard real-time applications are guaranteed to have their reserved CPU utilization in order to meet all their deadlines. The guarantee is independent of the behaviors of all other applications in the same system. We present the schedulability analysis methods on systems with or without shared memory.

Accountability Computing for E-society

In the business context, accountability has become a major concern for businesses around the world in aftermath of corporate scandals and fallouts. However, accountability has not been rigorously considered in IT system technologies and solutions. The goal of this study is to provide a clear understanding of accountability concept in service-oriented computing and, more generally, e-society. We first outline the general concept of accountability and presents a review on accountability from both management and IT perspective. We also clarify the ambiguity between the accountability concern and other architectural concerns such as security, QoS, trust and reputation.We present an SOA research project, the Llama accountability framework, which is an accountable service delivery infrastructure to support the monitoring, analysis, and reconfiguration of service processes. We believe such a framework will be useful for ensuring better e-services in an e-society.