Difference: SpectrumDM12RFC (3 vs. 4)

Spectrum 1.2 Proposed Recommendation: Request for Comments

Introduction

The Spectrum Data Model describes the structure of spectrophotometric datasets with spectral and temporal coordinates and associated metadata.

This update satisfies an enhancement request by IPAC to add support for the following use cases:

• 1-D spectra from Spitzer’s Infrared Spectrograph have multiple spectral orders
  • Spectral orders can overlap in wavelength
  • Plotting a Spitzer spectrum without accounting for orders gives you a mess
• SEDs often include limits on measurements
  • these can be upper or lower limits
  • Plotters need to indicate limits clearly to avoid scientific misunderstanding
  • SDM1.1 has an ad-hoc representation for upper limits (only) which may be usable, but is conceptually incorrect.

• Section 4.1.1: addition of 'order' and 'relorder' attributes
• Section 4.6.3: addition of 'UpperLimit' and 'LowerLimit' to explicitly express these concepts
• Corrected UTypes in VOTable example #1
• Updated diagrams to proper UML with improved consistency with the schema and text.

• https://www.ivoa.net/documents/SpectrumDM/20230907/index.html
  • associated schema: https://www.ivoa.net/xml/Spectrum/Spectrum-1.2.xsd

• https://github.com/ivoa-std/SpectrumDM

• https://wiki.ivoa.net/twiki/bin/view/IVOA/Spectrum

The DM working group consulted with the TCG prior to the start of this RFC and it was agreed that given

• this is a minor revision based on a specific institution request
• the request is targeted to serve a very specific purpose
• the model is not VO-DML compliant, so the level of effort required to produce additional implementations, serializations, validators is out of proportion to the impact of the RFE.

Data Providers:

• GAVO: Updated SSA Server to
  • include a PARAM with UTYPE="spec:Spectrum.Data.SpectralAxis.order" into each Spectrum Table.
  • also includes other changes/corrections from a review of the output against the Spectrum model document.
    • example file: http://dc.zah.uni-heidelberg.de/getproduct/flashheros/data_raw/ca98/blue/n0393.mt

• IPAC Firefly Archive toolkit:
  • "For some time, IPAC's Firefly archive GUI toolkit has taken advantage of IVOA Spectral Data Model (SDM) v1.1 to provide users with automatic plots of spectra that are the result of a query or have been uploaded to the tool. The plotting capability uses the SDM to identify which data to plot on the x and y axes and to change units. Firefly has recently been updated to recognize the new utypes specified in the proposed Spectral Data Model v1.2, namely:
    
    spec:Spectrum.Data.SpectralAxis.Order
    spec:Spectrum.Data.FluxAxis.Accuracy.LowerLimit
    spec.Spectrum.Data.FluxAxis.Accuracy.UpperLimit
    
    The toolkit uses these new utypes to plot orders (as found in e.g. Spitzer spectra) as separate traces, and to plot upper and lower limits as arrows (as found in e.g. SEDs). These changes are currently in test and will be released in May. Upon release, these features will be available in IRSA, Rubin, and NED interfaces, all of which are built upon the open-source Firefly toolkit.
    In a future release, Firefly will recognize the spec:Spectrum.Data.SpectralAxis.RelOrder utype proposed in SDMv1.2. When Firefly encounters a spectrum with only RelOrder and not Order, it will automatically plot each unique RelOrder as a different trace, analogous to how it treats Order. If a spectrum contains both Order and RelOrder, Firefly will automatically plot traces based on Order but will provide the user a toggle to plot RelOrder."

Since this is not a VO-DML compliant model, the mechanisms for

• validating the data model itself
• generating and validating example serializations in VOTable, XML, etc.
• generating model based code

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Comment by JesusSalgado

This is a preliminary comment: Version 1.0 had a java library implemented by Kelly McCusker (not in IVOA anymore) and Jonathan McDowell that allowed parsing and writing of spectral data compatible with 1.0. It would be great to obtain a version of this library and adapt it for these minor changes.

This library was used by some tools (e.g. VOSpec)

JesusSalgado - 2023-09-22

IG chairs or vice chairs are also encouraged to do the same, althought their inputs are not compulsory.