29-30 April 2004NVO Team Meeting NCSA 1

Data Access Layer (DAL)SSA, SIA Enhancement

Doug TodyNational Radio Astronomy Observatory

National Virtual Observatory

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Service Classes (Spectrophotometric Data)

SED Atlas or virtual

Spectrum Atlas or virtual

TimeSeries Atlas or virtual

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Query Interface

• Query Types– FindSED– FindSpectrum– FindTimeSeries

Any of SOAP, GET, POST depending upon service capabilities.Support for GET is required; SOAP and POST are optional.Query is the same regardless of the transmission protocol.

Query response (a VOTable) may differ for each class of object.

Each type of service is registered separately.All queries have the same basic arguments (so far).

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Query Interface

• Required Query Parameters– pos ra,dec (IRCS)– size diameter of aperture or search region– Format any; xml,votable,fits,text;

text/html; graphics; metadata

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Query Interface

• Optional Query Parameters– band band1[,band2,...] (RSM)– time lower,upper (units?)– aperture maximum or actual aperture size

(arcsec)(default: size)

– id dataset ID (global or service)– collection e.g., survey name– Class object class– spectralClass spectral class (source attr)– redshift lower,upper (source attr)

– Verbosity query response verbosity– rank all (default), top, N top items

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Query Response

• Rank default ordering of items (floating)• Title descriptive dataset title

• collection collection name, e.g., survey or instrument• datasetID global datasetID (query independent)• logical name logical dataset name (query relative)

• ra,dec aperture center coordinates, IRCS• aperture aperture diameter, arcsec• time.refValue mean time of observation (MJD)• time.loVal start of observation (MJD)• time.hiVal start of observation (MJD)• time.resolution resolution of time signal (sec)• spectral.ID filter or bandpass name• spectral.unit spectral unit• spectral.refValue characteristic spectral value• spectral.loVal lower limit of bandpass• spectral.hiVal upper limit of bandpass• spectral.resolution spectral resolution

• format spectra format (standard or collection-specific)• Acref URL used to access or retrieve dataset

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Service Metadata

• service class (SED, spectrum, timeSeries)

• service subclass (atlas or virtual data)• supported formats• supported query parameters• max search aperture• max object aperture

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Error Status

• SIA returns a VOTable containing an error code, if an error occurs.

• Should we return a HTTP error status instead of a VOTable?

• Error return for query is different than that for the dataset access

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SSA (Spectrophotometry?) Data Model

• At core is a Spectrophotometry object– Spectrum subclass has constant time and position– TimeSeries subclass has constant spectral coordinate

• SED is a set of Spectrum objects

• Curation, Coverage, Accuracy, Frame• SpectralCoordinate object

– type: wavelength, frequency, energy, etc.

• Flux object– type: flux density, intensity, counts, etc.

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SSA Data Formats

• VOTable– standard table format, extensible– one table per spectrum

• FITS– standard table format, extensible – bintable with row-per-spectrum for SED

• XML– native XML, for web services and XML tools

• text– simple text (no markup)

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Data Access Layer

• SIA V1.1 Priorities– Dataset provenance, Curation (collection, dataset

ID)– UCD normalization, UTYPE– Logical name feature– Ranking feature– Error handling

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DAL Roadmap

• Simple Catalog Access• Scope: Simple queries to individual catalogs (e.g., CS, SkyQuery)• More complex catalog operations, e.g., query portals, distributed• cross-matching, etc., are handled elsewhere within VO.

• Status: Current interface is Cone Search with no QL.• Relevant work is currently going on within the ADQL WG; we need• to determine how to recast portions of this as a DAL service.

• 1. Discuss plan for DAL integration of ADQL/SkyNode technology• at NVO team meeting Apr 30 for review by DAL WG at the May 24• Interop meeting.• 30-Apr-2004

• 2. Agree upon scope and plan for DAL catalog access service.• 30-May-2004

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DAL Roadmap

• Simple Image Access (SIA)• Scope: Access to 1-2D images and spectral image cubes.• Status: Defacto V1.0 of the SIA interface is in use but has• not yet been published as an IVOA standard.

• 1. Publish SIA V1.0 in its current form as a grand-fathered• (frozen) interface.• 31-Mar-2004

• 2. Agree on feature set for SIA V1.1 (limited to relatively minor• enhancement of V1.0). Begin discussion of requirements for general• image access beyond SIA.• 30-May-2004

• 3. Draft SIA V1.1 spec available for review.• 01-Aug-2004

• 4. Publish SIA V1.1 to REC status.• 30-Nov-2004

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DAL Roadmap

• Simple Spectral Access (SSA)• Scope: 1D spectra, SEDs, time series.• Status: Have internal V0.1 versions of query interface and• spectral data model. Working drafts still in preparation within• subgroups.

• 1. V0.5 working draft specification available for working group• discussion and trials.• 15-Apr-2004

• 2. V0.9 working draft specification available for working group• discussion and trials.• 15-May-2004

• 3. V1.0 working draft specification available for review.• 15-Jul-2004

• 4. Publish SSA V1.0 to REC status.• 15-Nov-2004