Modern scientific research is increasingly conducted by virtual communities of scientists distributed around the world. The data volumes created by these communities are extremely large, and growing rapidly. The management of the resulting highly distributed, virtual data systems is a complex task, characterized by a number of formidable technical challenges, many of which are of a software engineering nature. In this paper we describe our experience over the past seven years in constructing and deploying OODT, a software framework that supports large, distributed, virtual scientific communities. We outline the key software engineering challenges that we faced, and addressed, along the way. We argue that a major contributor to the success of OODT was its explicit focus on software architecture. We describe several large-scale, real-world deployments of OODT, and the manner in which OODT helped us to address the domainspecific challenges induced by each deployment.

Knowledge discovery and data correlation require a unified approach to basic data management. However, achieving such an approach is nearly impossible with hundreds of disparate data sources. legacy systems and data formats. This problem is pervasive in the space science community where data models, taxonomies and data management systems are locally implemented and limited metadata has been collected and organized. Technology developed by the Object Oriented Data Technology (OODT) task at NASA's Jet Propulsion Laboratory (JF'L) has been exploring component frameworks for managing, locating and exchanging data residing within a geographically distributed nehvork. OODT has taken a novel approach towards solving this problem by exploiting web technologies usually dedicated to e-commerce, combined with a rich, metadata-based environment. The components developed by OODT Create a set of distributed peer-to-peer services that allow for data managed by a peer to he searched and returned as part of an integrated data management system. This paper discusses the approach taken to develop a software framework, and two prototype development efforts for the Planetary Data System (PDS) and the Mission and Ground Asset Database.'

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