A Virtual Data Grid for LIGO

GriPhyN (Grid Physics Network) is a large US collaboration to build grid services for large physics experiments, one of which is LIGO, a gravitational-wave observatory. This paper explains the physics and computing challenges of LIGO, and the tools that GriPhyN will build to address them. A key component needed to implement the data pipeline is a virtual data service; a system to dynamically create data products requested during the various stages. The data could possibly be already processed in a certain way, it may be in a file on a storage system, it may be cached, or it may need to be created through computation. The full elaboration of this system will allow complex data pipelines to be set up as virtual data objects, with existing data being transformed in diverse ways. This document is a data-computing view of a large physics observatory (LIGO), with plans for implementing a concept (Virtual Data) by the GriPhyN collaboration in its support. There are three sections: • Physics: what data is collected and what kind of analysis is performed on the data. • The Virtual Data Grid, which describes and elaborates the concept and how it is used in support of LIGO. • The GriPhyN Layer, which describes how the virtual data will be stored and handled with the use of the Globus Replica Catalog and the Metadata Catalog.