Joachim Hammer

Template-based wrappers in the TSIMMIS system

In order to access information from a variety of heterogeneous information sources, one has to be able to translate queries and data from one data model into another. This functionality is provided by so-called (source) wrappers [4,8] which convert queries into one or more commands/queries understandable by the underlying source and transform the native results into a format understood by the application. As part of the TSIMMIS project [1, 6] we have developed hard-coded wrappers for a variety of sources (e.g., Sybase DBMS, WWW pages, etc.) including legacy systems (Folio). However, anyone who has built a wrapper before can attest that a lot of effort goes into developing and writing such a wrapper. In situations where it is important or desirable to gain access to new sources quickly, this is a major drawback. Furthermore, we have also observed that only a relatively small part of the code deals with the specific access details of the source. The rest of the code is either common among wrappers or implements query and data transformation that could be expressed in a high level, declarative fashion. Based on these observations, we have developed a wrapper implementation toolkit [7] for quickly building wrappers. The toolkit contains a library for commonly used functions, such as for receiving queries from the application and packaging results. It also contains a facility for translating queries into source-specific commands, and for translating results into a model useful to the application. The philosophy behind our “template-based” translation methodology is as follows. The wrapper implementor specifies a set of templates (rules) written in a high level declarative language that describe the queries accepted by the wrapper as well as the objects that it returns. If an application query matches a template, an implementor-provided action associated with the template is executed to provide the native query for the underlying source1. When the source returns the result of the query, the wrapper transforms the answer which is represented in the data model of the source into a representation that is used by the application. Using this toolkit one can quickly design a simple wrapper with a few templates that cover some of the desired functionality, probably the one that is most urgently needed. However, templates can be added gradually as more functionality is required later on. Another important use of wrappers is in extending the query capabilities of a source. For instance, some sources may not be capable of answering queries that have multiple predicates. In such cases, it is necessary to pose a native query to such a source using only predicates that the source is capable of handling. The rest of the predicates are automatically separated from the user query and form a filter query. When the wrapper receives the results, a post-processing engine applies the filter query. This engine supports a set of built-in predicates based on the comparison operators =,≠,<,>, etc. In addition, the engine supports more complex predicates that can be specified as part of the filter query. The postprocessing engine is common to wrappers of all sources and is part of the wrapper toolkit. Note that because of postprocessing, the wrapper can handle a much larger class of queries than those that exactly match the templates it has been given. Figure 1 shows an overview of the wrapper architecture as it is currently implemented in our TSIMMIS testbed. Shaded components are provided by the toolkit, the white component is source-specific and must be generated by the implementor. The driver component controls the translation process and invokes the following services: the parser which parses the templates, the native schema, as well as the incoming queries into internal data structures, the matcher which matches a query against the set of templates and creates a filter query for postprocessing if necessary, the native component which submits the generated action string to the source, and extracts the data from the native result using the information given in the source schema, and the engine, which transforms and packages the result and applies a postprocessing filter if one has been created by the matcher. We now describe the sequence of events that occur at the wrapper during the translation of a query and its result using an example from our prototype system. The queries are formulated using a rule-based language called MSL that has been developed as a template specification and query language for the TSIMMIS project. Data is represented using our Object Exchange Model (OEM). We will briefly describe MSL and OEM in the next section. Details on MSL can be found in [5], a full introduction to OEM is given in [1].

An Internet-based negotiation server for e-commerce

Abstract. This paper describes the design and implementation of a replicable, Internet-based negotiation server for conducting bargaining-type negotiations between enterprises involved in e-commerce and e-business. Enterprises can be buyers and sellers of products/services or participants of a complex supply chain engaged in purchasing, planning, and scheduling. Multiple copies of our server can be installed to complement the services of Web servers. Each enterprise can install or select a trusted negotiation server to represent his/her interests. Web-based GUI tools are used during the build-time registration process to specify the requirements, constraints, and rules that represent negotiation policies and strategies, preference scoring of different data conditions, and aggregation methods for deriving a global cost-benefit score for the item(s) under negotiation. The registration information is used by the negotiation servers to automatically conduct bargaining type negotiations on behalf of their clients. In this paper, we present the architecture of our implementation as well as a framework for automated negotiations, and describe a number of communication primitives which are used in the underlying negotiation protocol. A constraint satisfaction processor (CSP) is used to evaluate a negotiation proposal or counterproposal against the registered requirements and constraints of a client company. In case of a constraint violation, an event is posted to trigger the execution of negotiation strategic rules, which either automatically relax the violated constraint, ask for human intervention, invoke an application, or perform other remedial operations. An Event-Trigger-Rule (ETR) server is used to manage events, triggers, and rules. Negotiation strategic rules can be added or modified at run-time. A cost-benefit analysis component is used to perform quantitative analysis of alternatives. The use of negotiation servers to conduct automated negotiation has been demonstrated in the context of an integrated supply chain scenario.

SPEEDING UP MATERIALIZED VIEW SELECTION IN DATA WAREHOUSES USING A RANDOMIZED ALGORITHM

A data warehouse stores information that is collected from multiple, heterogeneous information sources for the purpose of complex querying and analysis. Information in the warehouse is typically stored in the form of materialized views, which represent pre-computed portions of frequently asked queries. One of the most important tasks when designing a warehouse is the selection of materialized views to be maintained in the warehouse. The goal is to select a set of views in such a way as to minimize the total query response time over all queries, given a limited amount of time for maintaining the views (maintenance-cost view selection problem). In this paper, we propose an efficient solution to the maintenance-cost view selection problem using a genetic algorithm for computing a near-optimal set of views. Specifically, we explore the maintenance-cost view selection problem in the context of OR view graphs. We show that our approach represents a dramatic improvement in time complexity over existing search-ba...

A three-tier architecture for ubiquitous data access

We present a three-tier architecture of middleware that addresses challenges facing accessibility, availability, and consistency of data in mobile environments. The architecture supports the automatic hoarding of data from multiple, heterogeneous sources into possibly a variety of different mobile devices. The middle tier enables the automation of synchronization tasks in both connected mode (following disconnection) and weakly connected mode, where only intelligent and effective synchronization can be used in the presence of a low-bandwidth network. We present the three-tier architecture based on the Coda file system.

A replicable Web-based negotiation server for e-commerce

This paper describes our ongoing R&D effort in developing a replicable, Web-based negotiation server to conduct bargaining-type negotiations between clients (i.e., buyers and sellers) in e-commerce. Multiple copies of this server can be paired with existing Web-servers to provide negotiation capabilities. Each client can select a trusted negotiation server to represent his/her interests. Web-based GUI tools are used by clients in a build-time registration process to specify the requirements, constraints, negotiation strategic rules, and preference scoring methods related to the buying or selling of a product. The registration information in used by the negotiation servers to conduct negotiations automatically on behalf of the clients. In this paper, we present the architecture of the negotiation server and the framework for automated negotiations, and describe a number of communication primitives, which make up the negotiation protocol. We have developed a constraint satisfaction processor (CSP) to evaluate a negotiation proposal against the registered constraints. An event-trigger-rule (ETR) server manages events and triggers the execution of strategic rules, which may relax constraints, notify clients, or perform other operations. Strategic rules can be added and modified at run-time to deal with the dynamic nature of negotiations. A cost-benefit analysis performs quantitative analysis of alternative negotiation conditions. We have implemented a prototype system to demonstrate automated negotiations among buyers and suppliers in a supply chain management system.

CubiST: a new algorithm for improving the performance of ad-hoc OLAP queries

Being able to efficiently answer arbitrary OLAP queries that aggregate along any combination of dimensions over numerical and categorical attributes has been a continued, major concern in data warehousing. In this paper, we introduce a new data structure, called Statistics Tree (ST), together with an efficient algorithm called CubiST, for evaluating ad-hoc OLAP queries on top of a relational data warehouse. We are focusing on a class of queries called cube queries, which generalize the data cube operator. CubiST represents a drastic departure from existing relational (ROLAP) and multi-dimensional (MOLAP) approaches in that it does not use the familiar view lattice to compute and materialize new views from existing views in some heuristic fashion. CubiST is the first OLAP algorithm that needs only one scan over the detailed data set and can efficiently answer any cube query without additional I/O when the ST fits into memory. We have implemented CubiST and our experiments have demonstrated significant improvements in performance and scalability over existing ROLAP/MOLAP approaches.

UbiData: ubiquitous mobile file service

One of the most challenging objectives of mobile data management is the ubiquitous, any time, anywhere access. This objective is very difficult to meet due to several network and mobile device limitations. Optimistic data replication is a generally agreed upon approach to alleviating the difficulty of data access in the adverse mobile environment. However, the two currently most popular models, both Client/Server and Peer-to-Peer models, do not adequately meet the ubiquity objectives. In our views, mobile data management should adequately support access to any data source, from any mobile device. It should also eliminate user involvement by automating data selection, hoarding, and synchronization, regardless of the mobile device chosen by the user. In this paper, we present UbiData: an application-transparent, double-middleware architecture that addresses these challenges. UbiData supports access and update to data from heterogeneous sources (e.g. files belonging to different file systems). It provides for the automatic and device-independent selection, hoarding, and synchronization of data. We present the UbiData architecture and system component, and evaluate the effectiveness of UbiDatas automatic data selection and hoarding mechanisms.

Element matching across data-oriented XML sources using a multi-strategy clustering model

We describe a family of heuristics-based clustering strategies to support the merging of XML data from multiple sources. As part of this research, we have developed a comprehensive classification for schematic and semantic conflicts that can occur when reconciling related XML data from multiple sources. Given the fact that element clustering is compute-intensive, especially when comparing large numbers of data elements that exhibit great representational diversity, performance is a critical, yet so far neglected aspect of the merging process. We have developed five heuristics for clustering data in the multi-dimensional metric space. Equivalence of data elements within the individual clusters is determined using several distance functions that calculate the semantic distances among the elements.The research described in this article is conducted within the context of the Integration Wizard (IWIZ) project at the University of Florida. IWIZ enables users to access and retrieve information from multiple XML-based sources through a consistent, integrated view. The results of our qualitative analysis of the clustering heuristics have validated the feasibility of our approach as well as its superior performance when compared to other similarity search techniques.

Making quality count in biological data sources

We propose an extension to the semistructured data model that captures and integrates information about the quality of the stored data. Specifically, we describe the main challenges involved in measuring and representing data quality, and how we addressed them. These challenges include extending an existing data model to include quality metadata, identifying useful quality measures, and devising a way to compute and update the value of the quality measures as data is queried and updated. Although our approach can be generalized to various other domains, it is currently aimed at describing the quality of biological data sources. We illustrate the benefits of our model using several examples from biological databases.

Remote-Exchange: an approach to controlled sharing among autonomous, heterogeneous database systems

The authors describe several aspects of the Remote-Exchange project, which focuses on an approach and experimental system for the controlled sharing and exchange of information among autonomous, heterogeneous database systems. The spectrum of heterogeneity which may exist among the components in a federation of database systems is examined, and an approach to accommodating such heterogeneity is described. An overview of the Remote-Exchange experimental system is provided, including the top level architecture, sharing mechanism, and sharing advisor.<<ETX>>