To:       ADEC Interoperability Working Group

   From:     John Good, Joe Mazzarella, Bruce Berriman

   Subject:  Alternative Plan for NASA Archive Interoperability

   We appreciate the work that Tom has put in getting the momentum
   going with his draft proposal.  Appropriate cross-referencing /
   cross-linking can indeed be very useful, but we think that we can
   make much greater progress towards the goal of true integration and
   inter-operability without excessive effort, and we would like to
   propose here a plan for doing so.

   While we concur with some basic elements of the original plan (such
   as the importance of providing an XML output), it does not seem to
   incorporate adequate interoperability at the level of basic data
   services, or bring us close enough to the broader goals of the NVO
   regarding an infrastructure for data exchange. With modest efforts,
   we believe that we can get where we want to be in a 6-9 month
   timeframe, bearing in mind that with the limited resources
   available to us, we can only affort to engage in new efforts that
   have material benefit for each of our centers individually and
   apart from forwarding the broader NVO goals.

   Rather than starting with an approach that focuses on linkage of
   Web forms, we think we should begin with a focus on the data
   services themselves.  Starting with some basic documentation and a
   directory of available services (URLs), combined with output
   options that supply data in 'raw' formats, a rich variety of data
   integration services can be easily constructed. Specifically, we
   suggest the following enhancements to our existing systems:

    1. Document Primary URL Data Services:

       If we can all agree on SOAP as a query request structure
       standard, we won't object. However, we suspect it will be a
       while before everyone has time to implement it, and the need is
       not yet pressing. URL-based request mechanisms will need to be
       maintained for years to come, to support queries issued from
       HTML forms via Web browsers.  Furthermore, most current data
       services require only a few simple keyword/value pairs, for
       which the URL mechanism works just fine whether issued from a
       Web browser or from a client computer program. There is little
       to be gained by adding the complexity of SOAP/XML for data
       requests until necessary to construct a specific distributed
       application. The main problem that most potential direct users
       of services have (besides the fact that they return HTML pages
       instead of raw data) is that there is often inadequate or no
       documentation of the services themselves. We need complete
       documentation of URL keywords, with appropriate values and
       ranges, etc., elevating the services to an "API" of sorts.  We
       therefore suggest that all current and future services be
       documented and maintained in this manner.

       For an example of what we mean, see the services described in
	  http://irsa.ipac.caltech.edu/applications/Oasis/svc/

2. Provide "Raw Data" Output Modes for Data Services:

       All services should provide a mode (or alternate service) that
       returns "raw" data.  By raw we mean a data stream containing a
       FITS image (e.g., MIME type image/x-fits) or spectrum, tabular
       data in either a flat ASCII data stream or - if we can agree on
       a consolidation of VOTable and XDF - an XML data stream. In
       some cases XML-based data constucts are better suited than
       ASCII or FITS tables, such as object attributes (and links to
       related data resources) in NED query reports, catalog lists,
       catalog data dictionaries, bibliographic reference lists, XY
       plots, data collections, etc.

    3. Integration Services:

       The role of "integration services" should be to give the data
       centers (and astronomers with sufficient programming skills)
       all they need to build data integration and knowledge discovery
       tools suited to their targetted needs. This is a key goal of
       the NVO that is well within reach if facilitated by the ADEC
       efforts as outlined below.

       One example functional enhancement of our services would be to
       construct a uniform set of services that return very quick
       summaries (estimates are acceptible) of the data available for
       a region of the sky.  For instance, if you were to ask IRSA for
       an inventory of its holdings withing 1 degree of M51, such a
       service would reply that there are about 3000 2MASS source, 2
       IRAS ISSA images, 100 2MASS images, etc.  NED would reply that
       it has approximately 106 galaxies, 3 galaxy clusters, 2 galaxy
       groups, 30 infrared sources, 1 QSO, 19 radio sources, 2
       supernovae, 2 visual sources, and 19 X-ray sources.

       Such a service should take only a few seconds to respond and if
       we structure the response correctly (XML), parallel responses
       from all archives could be merged before presentation.  We
       would also include, for each entry, the complete URL to the
       relevant data service.

       This is a fairly simple thing to implement; we have one example
       of a service that generates such statistics and most other
       centers have similar summary services.

       Each of us (and anyone else who is so motivated) will be free
       to use these services to collect and merge such inventories and
       present the result as appropriate for our user communities.
       Whether we format and present this composite inventory as a
       formatted HTML page or through a GUI; whether we go the next
       step and collect actual data and how we let the user tell us
       which subset of the data we want; and what we do with the data
       once we get it are all questions that should be left to the
       individual initiative of each center (or anyone else who wishes
       to build wrappers around our services).

       As an aside, we also point out that this can be the basis of a
       wider-reaching collaborative effort to define various "data
       collections" or "Concept Maps".

    4. Regarding GLU:

       Recent experience and success (as guaged by a high degree of
       user satisfaction with the 1-click data service links in NED's
       query reports (using positions and object names) and within the
       OASIS data integration workbench) indicates that direct URLs
       work fine, without the extra maintenance required to support
       GLU. In astronomy there just aren't that many resources to deal
       with, and they change infrequently enough that it is quite easy
       to keep URL dependencies in software up to date.

       If this situation changes and it becomes truly advantageous to
       add directory type servies for NASA archive services and for
       the more general VO, an approach that utilizes
       industry-standard XML-based solutions such as RDF, WSDL and
       UDDI is preferable over GLU, for reasons well stated in Timothy
       Kimbal's message on 01/07/2002.

   We believe that the above plan is workable in a 6-9 month period,
   provides truly new functionality (rather than being a rehash of
   existing capabilities) and, most importantly, it has both the
   appearance and reality of moving toward true archive service
   interoperability.