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An important aspect of scientific data management is metadata manage- ment One kind of metadata which needs special attention is data derivation information i e how data are generated In this paper we propose extensions to current database models to include implicit metadata management We introduce and analyze Derivation Nets an extension of Petri Nets as a tool to represent and manage data derivation relationships between scientific data and the procedures and algorithms that derive data We formulate the Derivation Net model study its properties with respect to database states and discuss the semantics of queries and updates within this framework Derivation Nets have been used to design the metadata manager portion of the Gaea scientific database management system Their operational character- istics implementation and sample use are described