link to NASA home page
NASA home page

link to GSFC home page
GSFC home page

link to GSFC Org page
GSFC organizational page

Responsible Official:
Dr. Joseph H. King, Code 633

Last Revised: Monday, 10-Dec-2001 14:37:17 EST [NAB]

CDF Releases Perl APIs and Embraces XML

By David Han

The CDF office realizes that scientific progress is often impeded by the lack of, or excessive multiplicity of, available standards for data formats and structures and/or data format translators. In a bid to facilitate and promote data sharing with other data formats, the CDF Office has recently decided to adopt eXtensible Markup Language (XML) as the basis for establishing interoperability with other scientific data formats. XML is a language defined by the World Wide Web Consortium (W3C), and it is an emerging technology for describing digital information (i.e. see, for example, http://www.xml.com/pub/a/98/10/guide0.html). XML is a method for putting structured data in a text file, and it is gaining support from a wide spectrum of users including academia, various government organizations, various technical committees, and commercial software companies such as Sun Microsystems and Microsoft.

The CDF office has developed an XML-based markup language called CDF Markup Language (CDFML) to describe CDF data and metadata. The CDFML employs some of the basic building blocks/objects defined in eXtensible Data Format (XDF) within CDF tags to describe CDF data and metadata. The use of these XDF objects allowed the CDF Office to capitalize on the existing infrastructure code already developed by the Astronomical Data Center (ADC) at NSSDC. XDF is an XML-based scientific data format and is considered by many to be the most mature Web-based scientific data format available today. As of this writing, software has been developed and tested to convert CDF data and metadata stored in CDFML into XDF. The CDF Office plans to develop software to export the contents of a CDF file into the CDFML format and vice versa in the near future.

The CDFML-to-XDF translation software mentioned above brings an unanticipated side benefit to the space physics user community. The XDF Office located at ADC has developed a program that converts a Flexible Image Transport System (FITS) file to the XDF format (using a markup language called FITSML). This means that since CDF understands how to interpret an XDF file, the interoperability between CDF and FITS can be achieved by defining a mapping relationship between the FITS objects and the CDF objects.