VOEvent References

[Rob Seaman]

Hi Rick,

Never too late!

Thanks!

Rob
--

On Mar 17, 2011, at 1:30 PM, Frederic V. Hessman wrote:

> Sorry for coming in so late, but I couldn't come in any sooner and I figured better late than never.  Since this may be too much too late, I'm sending it just to you.....
> 
> Rick
> 
> 1. ....
> 
> 	The <Reference> element has a more sophisticated notion of type -- referring mostly to the format of the referenced information - and semantic content.  The required "type" attribute is a general URI reference to a wide range of possible content formats rather than just a simple HTML link or "mime-like" acronym without any control over possible content.   The optional "content" attribute references a formal vocabulary, giving the reference a full astronomical meaning.
> 
> 3.3.1 ...
> 
> In VOEvent, these can be represented as:
> 
> <Param name="RATE_SIGNIF" value="20.49"  ucd="stat.snr" >
>    <Description>Best significance after trying all algorithms</Description>
>    <Reference type="vo://net.ivoa/vospace/core#html" uri="http://gcn.gsfc.nasa.gov/swift.html"/>
> </Param>
> 
> 3.5 ...
> 
> <How>
> 	 <Description> The Echelle spectrograph </Description>
> 	 <Reference uri="http://nsa.noao.edu/kp012345.rtml" type="vo://net.ivoa/vospace/voevent#rtml" />
> </How>
> 
> 3.9 <Reference> — External Content
> A <Reference> may be included in any element or sub-element of a VOEvent packet to describe an association with external content via a Uniform Resource Identifier [16].  In addition to the locator for the content, there are also two additional attributes describing the format and astronomical content of the reference.  In this way the semantic web can be connected to the VOEventNet.
> 
> The format is specified by the "type" attribute and should be a formal URI pointing to a controlled content description so that the format of the VOEvent packet can be interpreted without any human intervention or hard-wiring of the accessing software.  The formal description can be a formal IVOA-conformal vocabulary term [LINK] , e.g.
> 
> 	type="http://gcn.gsfc.nasa.gov/rdf/formats#SwiftByteStreamFormat"
> 
> (this attribute format requires no further specification) which represents the format only symbolically or via documentation of a formal data-model, or it can be a standard IVOA reference to typical format types conforming to the VOSpace specification (the VO equivalent of a "mime-type"):
> 
> 	type="vo://net.ivoa/vospace/core#fits"
> 
> (this attribute format requires that the namespace "vo" be defined previously in the VOEvent document).
> 
> 
> 
> The "content" attribute describes the astronomical meaning of the reference beyond questions of mere format and is given in the form of an IVOA-conformal vocabulary term [LINK].  This attribute gives the consumer of the VOEvent document semantic information necessary to know what the data represent: is the image a finder chart or a data image, is the VOTable a light curve or a spectrum?
> 
> Since the data format and astronomical content of a <Reference> is explicit and easily readable, both for humans and machines, there is no use for any element content.
> 
> 
> 
> 
> A <Reference> element has three attributes:
> 
> 3.9.1 uri — This is a link to another document in URI syntax.  There is no default value.
> 
> 3.9.2 type — This is the format of the document but also given in URI syntax so that an official type check can be made.  The default value is "net.ivoa/vospace/core#url".
> 
> 3.9.3 content — This attribute describes the astronomical meaning of the reference: this enables the VOEvent document to say whether the link is a light curve, a spectrum, a finder chart, or what.  This information is given in SKOS format conforming to the IVOA recommendations on astronomical vocabularies [Link], making it both human- and machine readable.  There is no default value.
> 
> A <Reference> should be used to provide general purpose ancillary data with a well-defined meaning. Here a fits image of a galaxy is presented (h.fits), a link to the data model that is needed for a machine to understand the meaning, and a semantic description for saying "galaxy" in a standardized machine-readable format.
> 
> 	<Group type="MyFilterWithImage"> <Reference uri="http://.../data/h.fits" type="http://.../data-models/#h-filter-image"  content="ivoat:galaxy" /> </Group>
> An example of the indirection of a VOEvent packet using <Reference>
> 
> 	<VOEvent ivorn="ivo://raptor.lanl#235649409/sn2005k" role="observation" version="2.0">
> 		 <Reference uri="http://raptor.lanl.gov/documents/event233.xml" type="vo:net.ivoa/vospace/voevent#voevent">
> 	</VOEvent>
> 
> In order to illustrate the concept of a tightly constrained reference, here is a table containing examples of types and contents of potential interest to VOEvent consumers:
> 
> 
> 
> 		Content				type= (without a namespace designation)		content=
> 
> 		--------------------------------------------------
> 
> 		VOEvent			net.ivoa/vospace/voevent#voevent				ivoat:supernova
> 
> 		FITS images			net.ivoa/vospace/core#fits						ivoat:image, ivoat:finderChart
> 
> 		FITS tables			net.ivoa/vospace/core#fits						ivoat:catalogue
> 
> 		JPEG images		net.ivoa/vospace/core#jpeg					ivoat:finderChart
> 
> 		VOTables[22]		net.ivoa/vospace/core#votable					ivoat:lightCurve
> 
> 		RTML documents[15]	net.ivoa/vospace/voevent#rtml					ivoat:observation, ivoat:telescope, ivoat:instrumentConfiguration
> 
> 		SQL queries			net.ivoa/vospace/voevent#sql					ivoat:image, ivoat:spectrum, ivoat:equatorialCoordinate
> 
> 		....