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All XTE (X-ray Timing Explorer) telemetry data will be archived in FITS Binary Tables. This collection of files, the XTE FITS DataBase (XFDB), will be turned into a hierarchical database consisting entirely of FITS tables, with various features aimed at facilitating easy navigation of the database. Three of these will be discussed.
Index Tables All data tables for a given observation are divided into 16 subsystems, each with its own index table which contains pointers to these data tables. At the top of the hierarchy, a Master Index table contains one row per observation, providing pointers to the Subsystem Index tables for that observation. Data from a particular instrument for a specific source can be located by finding the observation for that source in the Master Index. This will provide a pointer to the Subsystem Index for the requested instrument which, in turn, will point to the data tables that one is interested in. This system works as well for the entire XTE archive, as it does for a single-user, single-observation database. The hierarchy uses the {\tt EXTLEVEL} keyword.
Data Descriptors A Data Description Language (DDL) has been designed that allows each data item in a data table to be tagged with a unique string completely describing: the source of the data; the selection criteria used in collecting the data; and the structure of the data item. The design of the DDL allows application in a multi-mission environment.
Data Finder A tool will be implemented that allows a client to extract data from the XFDB through a transparent query mechanism, the XTE Data Finder (XDF). XDF translates the client's query specification into a set of data descriptors and selection criteria, which it will use to navigate the data base and select the desired data. There are various options with respect to the amount of processing XDF should perform on the extracted data before handing it to the client.
