Data Access Layer Working Group sessions Oct 16-17, 2003 at InterOpOct2003

Chair: Doug Tody [DT]

Minutes: Markus Dolensky [MD]

There were about 40 participants.

For a review of the material covered and agreements reached see the DAL WG summary presentation presented by D.Tody in Friday's plenary session.


Overview of DAL types of data, DT

The concept of the class hierarchy of DAL services agreed to in Cambridge was briefly reviewed. See slide 10 in the WG summary presentation.

SIA V1.1, DAL service infrastructure; key issues, DT

A number of active issues required for SIA V1.1 were discussed. See slides 11-20 in the WG summary presentation.
The issues discussed included:

  • dataset IDs including replica management, virtual data
  • component data models, data characterization, DM representation
  • access reference templating

Q: How to deal with uniqueness of a dataset identifier?
A: Within authority ID domain data IDs assigned by each authority. One 'can' state that a ID is a replica, but this is not ensured.

Q: How to state data quality?
A1: Part of data model and characterization of data.
A2: Resource metadata allows have basic quality description of data collection.

Q: What about IDs of OTF processed products?
A: Goes to deeper question of what does it mean to publish data to the VO?
IDs do not change, but data may go away.

Proposed evolutions for SIA, Francois Bonnarel

A proposal was made to add support to SIA for templating the access reference URL.

  • URL templates to get less verbose output
  • factorization of repetitive cell values
  • data model serialization
  • Question: Would XSLT or Xpath be the right way to implement URL template resolution?
  • Francois asks for feedback to be sent to

SSA Overview, DT

An introduction to the goals of the Simple Spectral Access interface (SSA) was presented. See slides 21-28 in the WG summary presentation.

General Agreements on SSA:

  • Provide uniform interface for both 1D spectra and SEDs
  • Develop uniform data model for both 1D spectra and SEDs
  • Service interface will be similar to SIA, CS (query/response, getData)

Data output formats will include at least text, VOTable, FITS, graphicsSSA will provide an opportunity to learn how to 1) map VO data models into multiple external representations, and 2) package actual datasets in XML/VOTable, including representing data models in XML.

SED Intro, MD

  • This lead to a discussion about properties and query parameters that SSA services should recognize and support. See presentation (.pdf, .ppt)
  • Some missing bits were identified:
    • definition how to group parameter blocks; i.e. chunks of points with common meta info
    • reference frame (e.g. velocity frame, rest frame)

Spectral Data Model, Jonathan McDowell

  • follow above link for intro to modeling effort
  • Suggestion: Use term "samples"
  • Note that model also is supposed to cover SEDs

SSA Issues (discussion)

  • add query parameter for spectral resolution
  • Suggestion: Find more use cases
  • About formats: VOtable, text, fits binary table or image, graphics

Q: Conversion support for units needed?
A: No.

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