The Science Data Archive (SDA) is a system for storing, retrieving, and analyzing ACS data products generated by the STScI (CALACS), ECF (grism) and GTO (APSIS) data pipelines. Stored data products will ultimately include calibrated images from CALACS, drizzle-combined images from APSIS, extracted grism spectra, output catalogs from SExtractor and BPZ, and documentation about the manner in which the data were processed. The SDA allows the user to retrieve image files, perform parametric searches of header keywords and output catalogs, graphically represent the data with line plots and histograms, and extract "postage stamp" images of individual objects within an imaged field. The SDA returns tabular and graphical results in a number of useful formats, including ASCII, CSV, TSV, HTML, XML, JPEG, PNG, and PDF.
The validity of the scientific results derived from the GTO data depends on the integrity of the data contained within the SDA. Data are ingested into the SDA when processed and documented through official releases of the data pipelines. This requirement ensures that the data products conform to defined standards, have documented pedigrees, and are reproduceable.
The SDA follows a three-layered, WWW-enabled database application model. The first layer comprises a Data Base Management System (DBMS) and a Mass Storage System (MSS), which respectively handle the indexing and physical storage of the data. The second layer contains the programs (executables) that reside on the WWW and DBMS servers and handle the I/O between the first and third tiers. The third layer is the WWW user interface (UI) through which the scientist retrieves images, queries the SDA, and views query results. Each layer is contructed modularly so that any one may be modified with little or no effect on the other two.
The SDA development group at JHU is:
