Storing GPS data at distributed archives provides users with benefits such as speedier local access, and regional or research-specific data support, but it can also increase confusion when supposedly identical files contain different header information or file content, regardless of how slight the differences. These problems will increase along with increases in regional networks. A cooperative arrangement which improves coordination of data holdings between GPS archives, combined with a basic but similar user interface, would provide data users with easier access to GPS data and metadata by allowing them to simply contact one center, instead of contacting all of them separately. We call this concept of an interoperable multi-archive system the "GPS Seamless Archive Center" or GSAC.

The strategy for a seamless GPS archive was developed by participants from ten archive centers at a workshop sponsored by the UNAVCO Facility on 11-12 November 1997. A summary of this workshop is at 11-12 Nov 1997 GPS Seamless Archive Meeting Notes. The primary output product from the workshop is the definition of tables used to identify specific data holdings, and mechanisms to access data from any data center in a standard manner. Although not specifically focused on the IGS data, we propose that identical methods would provide uniform access to any of the Operational, Local, Regional or Global Data Center's, and help resolve data identity, delivery and time-delay issues. Each participant in the GPS Seamless Archive Centers will maintain their individuality and bring their own strengths into play, yet provide the user community with a familiar and consistent data access look-and-feel to all archive holdings by providing standardized data access.

The workshop concluded that a process and necessary software tools must be developed to define where data might exist (monument location tables), and for what time ranges. A summary description and some software tools are available. Having this information in distributable tables means that historical information is as readily available as recent information - if a file changes for example due to discovery of an incomplete download which is later corrected, then the table can be updated when the file is replaced. And the process of identifying data existence, data file holdings, and changes would be standardized. Regardless of the size of the data provider, identical tools and processes would be used, improving data quality and usability.

These tools can be operated by anyone wishing to participate in the GSAC process. GSAC specifications are used to create specific tables showing data holdings for each archive. The tables are stored in a well defined manner to simplify information exchange. Some GSAC's will advertise their own data, but for data-user's convenience, other GSAC's will collect these "advertisements" and provide a common interface to search and retrieve data from any of the GSAC data areas. A data requester can go to any GSAC, search the holdings-tables of all GSAC archives, and make a data request to the archive with the desired data. An overview of the GSAC concept is given in 1998 Hand Out. A follow-on GSAC meeting will be held in early 1999 to define data request mechanisms which will allow users to obtain data from any GSAC, regardless of where the data may physically reside.

Comments or questions about this page? Send e-mail to Lou Estey (louunavco.org).

Last modified Thursday, 17-Nov-2005 04:21:00 UTC

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