Ming-Chien Shan

The Pegasus heterogeneous multidatabase system

Pegasus, a heterogeneous multidatabase management system that responds to the need for effective access and management of shared data across in a wide range of applications, is described. Pegasus provides facilities for multidatabase applications to access and manipulate multipole autonomous heterogeneous distributed object-oriented relational, and other information systems through a uniform interface. It is a complete data management system that integrates various native and local databases. Pegasus takes advantage of object-oriented data modeling and programming capabilities. It uses both type and function abstractions to deal with mapping and integration problems. Function implementation can be defined in an underlying database language or a programming language. Data abstraction and encapsulation facilities in the Pegasus object model provide an extensible framework for dealing with various kinds of heterogeneities in the traditional database systems and nontraditional data sources.<<ETX>>

Enterprise workflow resource management

Resource management is a key issue in providing resource independence and efficient use of workflow resources. This paper outlines a design of such a resource management system for enterprise workflow environments. It is capable of handling a large number of workflow resources that are independently managed by pre-existing resource systems. It integrates these external resource systems at the schema level without duplicating individual resource information. Resource specification is greatly simplified by providing process designers with integrated views of enterprise workflow resources at different levels based on a unified resource model. Dynamic behaviors of workflow resources are supported through powerful resource policies.

An overview of Pegasus

Pegasus is a multidatabase management system. It provides access to multiple, autonomous, heterogeneous, distributed database management systems through a uniform interface by integrating native and various external databases. The external databases can have different data models, query languages, and world-views. The authors present an overview of the Pegasus system and highlight its main features.<<ETX>>

Automatic importation of relational schemas in Pegasus

The paper describes a technique for importing automatically an external relational schema into Pegasus, a heterogeneous, multidatabase system. The Pegasus data model is a functional object model which supports specialization, object-identity, and nested aggregation. The import algorithm generates the definition of a Pegasus schema which captures the semantics of a relational schema containing information about primary keys and referential integrity constraints. The algorithm described can be adapted easily for other semantic and object-oriented data models.<<ETX>>

Object Identification in Multidatabase Systems

Abstract In the Pegasus prototype multidatabase system, the key to the problem of object identity is a differentiation between the view of a data administrator, capturing all the underlying discrepancies and their solutions, and the view of an end user or application, in which only a consistent result is visible. New language constructs with which the administrator can describe solutions to identity problems include underlying and unifying types, the Image function, and producer types.

Multidatabase management in Pegasus

Pegasus is an object-oriented multidatabase system being developed at Hewlett-Packard Laboratories. The goal of the system is to provide facilities for multidatabase applications for accessing and manipulating multiple autonomous heterogeneous object-oriented, relational and other databases. This paper gives an overview of the architecture, describes the common object model and gives the justification for adapting the model for a multidatabase system. It describes the database environment of the system, discusses how to manage schemas consisting of types and functions from multiple databases. It briefly describes the features of the data language and gives an example. It discusses a method for dealing with object identification issues in a multidatabase system, reviews schema integration issues and briefly mentions schema mapping to relational models.<<ETX>>

Pegasus: a system for seamless integration of heterogeneous information sources

Pegasus, a heterogeneous multidatabase management system that is under development, is described. The goal of the system is to provide facilities for applications to access and manipulate multiple autonomous heterogeneous object-oriented, relational, and other information systems. Pegasus defines a common object model for unifying the data models of the underlying systems. The data language of Pegasus allows transparent as well as explicit access to multiple information systems in a single declarative statement. The Pegasus architecture is described, and attention is given to data integration and query processing in Pegasus.<<ETX>>

Value dates for concurrency control and transaction management in interoperable systems

Value dates appear, at present to be the most flexible concurrency control paradigm for autonomous heterogeneous interoperable systems. The protocols are deadlock free, and can be livelock free in the situation when the two-phase locking protocol (2PL) creates a deadlock in practice. Value dates accommodate the autonomy better. The commit protocols possible with value dates can be also more efficient than the two-phase commitment protocol (2PC). The advantages of the value dates make it worth the replacement of 2PL as the standard. Further research should concern the implementation issues. Another important issue is the use of unsafe values. Applications often use unsafe values with value dates for better efficiency, e.g. reservation systems.<<ETX>>

Database research at HP labs

Database research at HP Labs has focused in the last few years on the productive application development and use of database systems. The approach centered on developing a rich database model for expressing the semantics and behavior of information. The Iris object-oriented database management system is the result of that e ort. Iris combines the advantages of object-oriented concepts with database functionality. The advent of open systems and fast networks has fostered the belief that information is available at ones ngertips. Yet these advances have pointed to heterogeneity as the most serious challenge to programmer and knowledge worker productivity. Heterogeneous database systems must resolve the semantic discrepancies between di erent databases, handle the conversions between multiple data models, schemas and formats, etc., while preserving the autonomy of the underlying systems. Preserving the autonomy of the component databases is essential because they are supplied by di erent vendors or are large systems that took many years to develop, which makes modifying them either impossible or impractical. There is another class of data management systems that database researchers have not attempted to integrate, and yet these systems manage the bulk of data currently stored on computer systems. They are the specialized database systems such as spatial, geographical and CAD/CAM DBMSs. These customized systems were developed and optimized to meet the performance requirements of their respective applications. A new challenge is to interoperate these heterogeneous database systems while preserving their performance requirements. In integrating this class of systems, preserving their autonomy is no longer the primary requirement, but rather preserving the performance of the integrated system. Exploiting parallel and distributed execution is essential for meeting/exceeding the performance requirements for the integrated systems. We view autonomy and performance as two requirements of heterogenous databases at two ends of a spectrum where one must be traded to obtain the other. This report describes the highlights of the Iris work and the current database research e orts in tradi-