Elke A. Rundensteiner
Computer Science Department, Worcester Polytechnic Institute
100 Institute Rd, Worcester, MA 01609
Phone: (508) 831-5815, Fax: (508) 831-5776
E-mail: rundenst@cs.wpi.edu

Project Award Information
Award Number: IIS-9796264; Duration: 9/01/1994 - 8/31/2001 (5 years with one year extension), in fifth year; Title: NYI: Object-Oriented Database Tools for Supporting Evolutionary Software Systems

Object-Oriented Databases, Object-oriented Views, Schema Evolution, Interoperability.

Project Summary
This project investigates transparent schema change technology that allows for on-line modification of databases without disturbing existing applications. The methodology to tackle this problem is to integrate schema evolution and view support into one system. The resulting tool supports schema changes through a view rather than on the global schema, and preserves existing views through such changes. Within this proposed framework of transparent schema change, this project explores the following issues: (1) develop object-oriented view technology, (2) integrate view and schema evolution concepts into one mechanism supporting complex transformations; (3) develop algorithms for complex schema transformations as well as for transparent evolution; (4) develop and compare different OODB-based frameworks suitable for view and schema evolution support, (5) develop optimization strategies for view evolution, (6) perform experimental studies to evaluate the relative effectiveness of the proposed techniques, and (7) lastly extend the concepts and tools developed above as middle-layer services to distributed environments.

Publications and Products
The MultiView OO View system has been demonstrated (ACM SIGMOD'96) and its source code released during earlier stages of this project, More recently, SERF (Schema Evolution through an Extensible, Re-usable and Flexible the Web: Web Site Management Made EasyFramework) based on ODMG standard has been demonstrated (ACM SIGMOD'99+2000) and its source code will be released as freeware shortly.

Selective recent publications include :

Project Impact
Impact on Human Resources. This project has partially funded several Ph.D. students in my database research groups: Harumi A. Kuno (female), Summer 1996, is working at HP   Research Labs, Palo Alto in Cal. Young-Gook Ra (male), 1997 is working at Samsung Data Systems, Korea. Data Sun.  Jyh-Liang Amy Lee (female), has accepted a  tenure track faculty position at the Hong Kong University of Science and Technology this year.  Currently one new Ph.D.  student at WPI, Kajal Claypool, numerous Master students and undergraduate students  are involved.
Impact on education and curriculum development at all levels. This project has increased education at the undergraduate level by providing small projects into which we actively can involve undergraduate students via REUs and directed study projects. It has also enhanced our graduate courses, e.g, the Advanced Database course at WPI.
Industry. We have had several interactions, including on-site visits, with PSE team at Object Design Inc. They provided us with a copy of the PSE software augmented with a customized patch.
Impact. Increased interoperability, ease in migration of software over time, as well as the possibility of interfacing to legacy databases more effectively are critical problems faced by software industry. Our project promises to provide practical solutions to these important goals. In particular the invention of the SERF framework this past year is a significant result as it is the first approach to providing extensible yet consistent evolution support. SERF has multiple important applications, ranging from schema evolution of one central system, to mapping between two heterogeneous databases or even data models (migration), to functioning as middle-layer technology by integrating multiple data sources and producing views.

Goals, Objectives, and Targeted Activities
Last Year's Selected Accomplishments
Our general goal is to increase interoperability between evolving software applications, ease migration of software over time, as well as increase the possibility of interfacing to legacy databases more effectively by means of OODB technology. Highlights of our accomplishments achieved include:
SERF Framework for Extensible Schema Evolution Support. While current OODB systems only offer a fixed set (taxonomy) of primitive schema evolution operations, there has been work in recent years to try to define more complex evolution operations, such as merge-classes, transform-object-to-value. We instead have developed the first solution approach for enabling the support of arbitrarily complex schema evolution customized to user's needs. Our solution framework, called SERF (Schema Evoluton using Extensible, Re-usable, and Flexible Framework), is based on the general strategy to integrate a fixed set of primitive change operations with ODMG's object-query language (OQL) as vehicle for flexible object migration. The SERF framework has been designed and implemented to test its feasibility and limitations. SERF has been formally demonstrated at ACM SIGMOD 1999, and the XML-based web management system build using SERF technology has been accepted for demonstration at ACM SIGMOD 2000.
SERF Optimization: OQL Embedded with Evolution Methods. Within our SERF system, complex schema evolution templates can correspond to a sequence of OQL statements with embedded schema evolution and update methods. We have developed a technique, called OTO, for optimizing the performance of such complex OQL-based transformations. Based on dependency analysis, OTO exploits specific properties of schema evolution methods allowing pairs of them to be merged, cancelled or eliminated. We have proven our optimization strategy to be optimal. We have run studies to assess the potential gains of our optimization strategy on top of PSE (Persistent Storage Engine) by Excelon Inc (formerly known as Object Design Inc.)

Targeted Project Activities
Application of SERF Technology. In the remaining year, we'll wrap up our project by applying the SERF technology to additional applications to evaluate its promise and limitations. Possible avenues include flexible XML-based web site management, e-business applications, and heterogenous systems integration. Tools to facilitate such application such as visual frontends for transformation generation and visual template library browsing may be explored.
Advanced Extensions of SERF Technology. Time permitting, we may also investigate advanced extensions of SERF. This may include transparently performing such complex SERF-transformations to layers of view derivation (instead of the base schema shared by multiple users) to enable distributed collaboration-systems.

Project References
See above "Products" category for a listing of recent project reports, software and demonstrations. Those and related products can also be downloaded and/or viewed from our Database Systems Research Group homepage: http://davis.wpi.edu/dsrg

Area Background
The area of this project is object-oriented database systems. OODBs offer powerful and flexible modeling support to handle the needs of diverse application domains, including modeling constructs, such as classes, abstractions, inheritance, reuse, and behavioral modeling. Thus, typically OODBs are being used as foundation when developing (re-usable) database support for application-specific features, such as spatial data or history management. One important issue for databases in general and for OODBs in particular is schema evolution, the modification of the schema and the associated application data during the lifetime of a database system. Most work in the literature focussed on the realization of schema evolution operations in the context of a particular data model or even OODB, such as, Objectstore, Gemstone, Ithasca, or O2. Support is restricted to primitive evolution support only. Our project extends this previous work now providing complex extensible evolution support, as well as transparency of executing such schema changes on a shared OODB while minimally impacting existing applications.

Area References

Potential Related Projects. Object-Oriented Database Systems.