Darrell Woelk

InfoSleuth: agent-based semantic integration of information in open and dynamic environments

The goal of the InfoSleuth project at MCC is to exploit and synthesize new technologies into a unified system that retrieves and processes information in an ever-changing network of information sources. InfoSleuth has its roots in the Carnot project at MCC, which specialized in integrating heterogeneous information bases. However, recent emerging technologies such as internetworking and the World Wide Web have significantly expanded the types, availability, and volume of data available to an information management system. Furthermore, in these new environments, there is no formal control over the registration of new information sources, and applications tend to be developed without complete knowledge of the resources that will be available when they are run. Federated database projects such as Carnot that do static data integration do not scale up and do not cope well with this ever-changing environment. On the other hand, recent Web technologies, based on keyword search engines, are scalable but, unlike federated databases, are incapable of accessing information based on concepts. In this experience paper, we describe the architecture, design, and implementation of a working version of InfoSleuth. We show how InfoSleuth integrates new technological developments such as agent technology, domain ontologies, brokerage, and internet computing, in support of mediated interoperation of data and services in a dynamic and open environment. We demonstrate the use of information brokering and domain ontologies as key elements for scalability.

A model of authorization for next-generation database systems

The conventional models of authorization have been designed for database systems supporting the hierarchical, network, and relational models of data. However, these models are not adequate for next-generation database systems that support richer data models that include object-oriented concepts and semantic data modeling concepts. Rabitti, Woelk, and Kim [14] presented a preliminary model of authorization for use as the basis of an authorization mechanism in such database systems. In this paper we present a fuller model of authorization that fills a few major gaps that the conventional models of authorization cannot fill for next-generation database systems. We also further formalize the notion of implicit authorization and refine the application of the notion of implicit authorization to object-oriented and semantic modeling concepts. We also describe a user interface for using the model of authorization and consider key issues in implementing the authorization model.

Architecture of the ORION next-generation database system

Various architectural components of ORION-1 and ORION-1SX are described and a review of the current implementation is provided. The message handler receives all messages sent to the ORION system. The object subsystem provides high-level data management functions, including query optimization, schema management, long data management (including text search) and support for versionable objects, composite objects, and multimedia objects. The transaction management subsystem coordinates concurrent object accesses and provides recovery capabilities. The storage subsystem manages persistent storage of objects and controls the flow of objects between the secondary storage device and main memory buffers. In ORION-1, all subsystems reside in one computer. The ORION-1SX architecture is significantly different from ORION-1 in the management of shared data structures and distribution of these subsystems and their components. >

Composite object support in an object-oriented database system

Many applications in such domains as computer-aided design require the capability to define, store and retrieve as a single unit a collection of related objects known as a composite object. A composite object explicitly captures and enforces the IS-PART-OF integrity constraint between child and parent pairs of objects in a hierarchical collection of objects. Further, it can be used as a unit of storage and retrieval to enhance the performance of a database system. This paper provides a formal definition of the semantics of composite objects within an object-oriented data model, and describes their use as units of integrity control, storage and retrieval, and concurrency control in a prototype object-oriented database system we have implemented.

An object-oriented approach to multimedia databases

This paper identifies data modelling and data access and sharing requirements which multimedia applications impose on a database system. It shows the capabilities of an object-based data model and indicates extensions which are needed to meet the data modelling aspects of these requirements. A logical implementation of the operations on the model is described. The model generalizes the notions of instantiation and generalization in the standard object-oriented paradigm, and augments it with the notions of aggregation and relationships which are specialized for a multimedia application environment. Objects may exist in aggregation hierarchies which provide the capability to integrate diverse types of multimedia information such as text, sound, bit-mapped images, and complex graphics drawings. Objects may also be linked through other user-defined relationships to capture such application functions as voice annotation and referencing of one document by another. Using this model, the semantics of aggregation and relationships in a multimedia application environment can be understood and efficiently supported by a database system.

A distributed object-oriented database system supporting shared and private databases

ORION-2 is a commercially available, federated, object-oriented database management system designed and implemented at MCC. One major architectural innovation in ORION-2 is the coexistence of a shared databese and a number of private databases. The shared database is accessible to all authorized users of the system, while each private database is accessible to only the user who owns it. A distributed database system with a shared database and private databases for individual users is a natural architecture for data-intensive application environments on a network of workstations, notably computer-aided design and engineering systems. This paper discusses the benefits and limitations of such a system and explores the impact of such an architecture on the semantics and implementation of some of the key functions of a database system, notably queries, database schema, and versions. Although the issues are discussed in the context of an object-oriented data model, the results (at least significant portions thereof) are applicable to database systems supporting other data models.

Query processing in distributed ORION

In this paper we describe query processing strategies we have developed and implemented in the distributed version of the ORION object-oriented database system. The ORION query model is based on the ORION object-oriented data model. Further, we have adopted the response time as the primary objective function for query optimization. The query-processing strategies we have developed reflect our solutions to these requirements. In particular, our strategies are based on a dataflow execution model which represents a plan for executing a query concurrently at multiple sites. One important observation we bring out in our description of the ORION query-processing strategies is that most of the important techniques developed for optimizing and processing a relational query apply directly to an object-oriented query, despite the differences in the underlying data models.

A Model of Authorization for Object-Oriented and Semantic Databases

This paper presents a formal model of authorization for use as the basis for an authorization mechanism in ORION, a prototype database system which directly supports the object-oriented paradigm and a number of semantic data modeling concepts. The model extends in two significant ways the existing models of authorization, which have been designed for database systems supporting the relational, network, or hierarchical models of data. First, it fully develops the concept of implicit authorization, introduced in an earlier paper [FERN75b], to help solve the storage requirement of representing all authorizations in a system by allowing the system to deduce authorizations from explicitly stored authorizations, and to provide a basis for detecting authorization definitions which conflict with existing authorizations. Second, it provides a formal basis for accommodating a number of modeling concepts which the existing models of authorization cannot address: the IS-PART-OF relationship between an object and its containing object, and versions of an object.

The Carnot Heterogeneous Database Project: Implemented Applications

The Carnot project was an ambitious research project inheterogeneous databases. It integrated a variety of techniques toaddress a wide range of problems in achieving interoperation inheterogeneous environments. Here we describe some of the majorimplemented applications of this project. These applications concern(a) accessing a legacy scientific database, (b) automating a workflowinvolving legacy systems, (c) cleaning data, and (d) retrievingsemantically appropriate information from structured databases inresponse to text queries. These applications support scientificdecision support, business process management, data integrityenhancement, and analytical decision support, respectively. Theydemonstrate Carnot‘s capabilities for (a) heterogeneous queryprocessing, (b) relaxed transaction and workflow management, (c)knowledge discovery, and (d) heterogeneous resource modelintegration.

Using Carnot for enterprise information integration

The Carnot Project, which addresses the problem of logically unifying physically distributed, enterprise-wide, heterogeneous information is discussed. Specifically, Carnot will provide a user with the means to navigate information efficiently and transparently, to update that information consistently, and to write applications easily for large, heterogeneous, distributed information systems. The Carnot architecture and the Carnot tools for building applications are described.<<ETX>>