Jin Hyun Son

Improving the performance of time-constrained workflow processing

Abstract Many workflow applications often have timing constraints such that each processing of a workflow needs to be finished within its deadline. There have been some works to improve the performance of time-constrained workflow processing such as predictive workflow scheduling. They, however, have not much considered appropriate analyses to determine the processing capacities for certain activities so that most workflow instances can satisfy the deadline. Our objective in this paper is to address a suitable scheme that can maximize the number of workflow instances satisfying the given deadline. We first present a method to find out a set of critical activities where a critical activity is the one whose delay of completion directly affects the overall processing time of a workflow. Since each critical activity must have a certain number of servers for the sufficient processing capacity, we then develop a method to determine the minimum number of servers (MNS) for the critical activity such that this activity should be finished without delay for a given input arrival rate. We show through performance experiments that our method can be effectively utilized in practice.

A scalable publish/subscribe system for large mobile ad hoc networks

Since nodes that compose mobile ad hoc networks (MANETs) does not have any prior knowledge about other nodes in many cases, the publish/subscribe communication paradigm that has the decoupling and asynchrony properties can be useful to share information between nodes. Existing publish/subscribe services for MANETs can be categorized into document flooding (DF), destination-based routing (DBR), and content-based routing (CBR). Although those approaches may work well when the size of network is small, all of them suffer from the performance decline as the size of the network increases. In this paper, we compare those approaches, and then propose a scalable publish/subscribe communication scheme in large MANETs by combining DF and CBR hierarchically. Our approach is to cluster all nodes in networks and to exploit CBR and DF for the intra- and inter-cluster communication, respectively. By using this approach, we can effectively utilize benefits of both approaches. Then, we present performance evaluation results which validate our idea with respect to system performance and scalability.

Extracting the workflow critical path from the extended well-formed workflow schema

The critical path in a workflow schema is defined as the longest execution path from the start activity to the end activity. It can be utilized in many workflow issues such as workflow resource and time management. However, little work has been done on the critical path in a workflow because workflow control flows are much more complex than those represented with ordinary graphs and networks. In this paper, we first describe our workflow model with a set of workflow control constructs that provide sufficient power to express the models of most of todays business processes. Then, we propose a systematic method of identifying the critical path for a given workflow schema. Our proposed method is based on queuing theory because operational characteristics of the workflow schema can be modeled by a M/M/1 queuing network.

Critical path identification in the context of a workflow

Abstract The concept of the critical path has been widely discussed in many areas of computer engineering such as parallel and distributed programs, a computer circuit, and a directed acyclic graph. The critical path analyzes in a workflow can allow us to utilize it in many workflow issues, especially workflow resource management and workflow time management. In this paper, we first describe our workflow model using the workflow queuing network. Then, we propose a method to systematically determine the critical path under the workflow model, and give an overall example that shows how our method works. In addition, several experiments are made to evaluate the accuracy of the critical path found.

Efficient incremental view maintenance in data warehouses

In the data warehouse environment, the concept of a materialized view is nowadays common and important in an objective of efficiently supporting OLAP query processing. Materialized views are generally derived from select-project-join of several base relations. These materialized views need to be updated when the base relations change. Since the propagation of updates to the views may impose a significant overhead, it is very important to update the warehouse views efficiently. Though various view maintenance strategies have been discussed so far, they typically require too much access to base relations, resulting in the performance degradation.In this paper we propose an efficient incremental view maintenance strategy called delta propagation that can minimize the total size of base relations accessed by analyzing the properties of base relations. We first define the delta expression and a delta propagation tree which are core concepts of the strategy. Then, a dynamic programming algorithm that can find the optimal delta expression are proposed. We also present various experimental results that show the usefulness and efficiency of the strategy.

An analysis of the optimal number of servers in distributed client/server environments

In the client/server model for distributed on-line requests processing, the concept of a server class that consists of multiple identical servers is often provided for the fast response time, high fault-tolerance, or continuous availability. As far as we are aware of, there is no concrete formulation that provides the optimal number of servers of a server class in distributed client/ server systems. The number of servers has been usually chosen only by heuristic methods or statistics after monitoring system behavior for some periods of time.In this paper, we propose a method based on queuing theory that determines the optimal number of servers in a server class for a general distributed client/server model that encompasses the state-of-the-art on-line transaction processing environment described in the literature.

Hierarchically organized skew-tolerant histograms for geographic data objects

Histograms have been widely used for fast estimation of query result sizes in query optimization. In this paper, we propose a new histogram method, called the Skew-Tolerant Histogram (STHistogram) for two or three dimensional geographic data objects that are used in many real-world applications in practice. The proposed method provides a significantly enhanced accuracy in a robust manner even for the data set that has a highly skewed distribution. Our method detects hotspots present in various parts of a data set and exploits them in organizing histogram buckets. For this purpose, we first define the concept of a hotspot, and provide an algorithm that efficiently extracts hotspots from the given data set. Then, we present our histogram construction method that utilizes hotspot information. We also describe how to estimate query result sizes by using the proposed histogram. We show through extensive performance experiments that the proposed method provides better performance than other existing methods.

DEADLINE ALLOCATION IN A TIME-CONSTRAINED WORKFLOW

Workflow management systems should efficiently manage workflow constraints such as time, resource, and cost during workflow executions. Especially, workflow time management is important in timely scheduling of workflow process execution, avoiding deadline violations, and improving the workflow throughput. Though there have been some studies on the dynamic deadline management in a workflow, the importance of the static deadline management has not been much addressed in the past. We first describe our workflow model considered in this paper. Then, we propose a static deadline allocation method that can facilitate an efficient workflow processing. The proposed method can achieve high workflow throughput by analyzing the interrelated workflow components. We also present various experimental results that show the usefulness and efficiency of the method.

Rule-based Dynamic Business Process Modification and Adaptation

The advances in ubiquitous computing technologies have given rise to the u-Business, where we obtain business-related context information from ubiquitous devices to adapt to the changes of business environments in a timely manner. In these rapidly changing u-Business environments, we need a mechanism to modify business process schemas, which represent a group of business activities arranged in a meaningful way to give values to the u-Business. We also need a way to migrate running process instances to their new business process schemas. In this paper, we propose a rule-driven approach for dynamic business process schema modification and instance adaptation. The proposed approach uses rules to describe schema modification operations to be applied and rule execution conditions. Business environment changes are encoded in these rules, thus timely schema modification is possible. We also propose a system architecture for realizing this rule-driven approach. We have designed the system architecture by utilizing existing technologies so that the system can be easily implemented.

Semantic Business Registry Information Model

For the intelligent business process management, ebXML registry needs to efficiently store and process semantic information. Even though ebXML registry provides two basic information models to define and associate semantics between registry objects; e.g., classification information model and association information model, they cannot express all semantics of the standard Web ontology language (OWL) due to their generic differences in design goals and usage patterns. To support OWL semantics in ebXML registries is to provide a foundation for intelligent information processing in ebXML registries. In this paper, we address how to embed OWL semantics in the ebXML registry. To express OWL constructs in ebXML registries, we propose a new ebXML registry information model, i.e., a semantic information model (SIM).