XML at the ADC: Steps to a Next Generation Data Archive

The eXtensible Markup Language (XML) is a document markup language that allows users to specify their own tags, to create hierarchical structures to qualify their data, and to support automatic checking of documents for structural validity. It is being intensively supported by nearly every major corporate software developer. Under the funds of a NASA AISRP proposal, the Astronomical Data Center (ADC, http://adc.gsfc.nasa.gov) is developing an infrastructure for importation, enhancement, and distribution of data and metadata using XML as the document markup language. We discuss the preliminary Document Type Definition (DTD, at http://adc.gsfc.nasa.gov/xml) which specifies the elements and their attributes in our metadata documents. This attempts to define both the metadata of an astronomical catalog and the `header' information of an astronomical table. In addition, we give an overview of the planned flow of data through automated pipelines from authors and journal presses into our XML archive and retrieval through the web via the XML-QL Query Language and eXtensible Style Language (XSL) scripts. When completed, the catalogs and journal tables at the ADC will be tightly hyperlinked to enhance data discovery. In addition one will be able to search on fragmentary information. For instance, one could query for a table by entering that the second author is so-and-so or that the third author is at such-and-such institution.