Query message format

[Tony Linde]

Hi Ray,

> In my opinion, the most important requirement of the query 
> interchange 
> format is that it be easily converted into other forms. 

Or, to restate, that it can be parsed and applied to different data
stores? But it'd probably be more time consuming to write parsers for
XQuery than translators of some XML format.

Perhaps we need a 2-tier VOQL: if the metadata for the all datasets
being queried says that they can all accept XQuery format queries, then
the user formulating the query has a rich interface but if any does not
have that, then the query format and interface is reduced to cope.

>    *  an ASU query to an ASU interface
>    *  an SIA query to an SIA interface
>    *  a JVO query to the JVO grid.  

I don't know these. Isn't ASU an intermediate query interface which VOQL
would supplant? And SIA is still a proposal and will presumably be
amended to fit the standards? What is JVO?

> The idea is that it would be 
> straightforward, in theory, to transform the XML-encoded query 
> into XML Query and thereby accept queries from "outside" AstroGrid.  

I don't think there'll be an 'AstroGrid' to be outside of. More a matter
of those data centres which choose to use some of the AstroGrid
components (possibly mixed with those from NVO, home grown ones etc.).
That's why the interchange formats are important.

One component of any VO will be a query construction interface (part of
whichever portal or client the user chooses). This interface will know
which data sources are being addressed by the query and will have to
decode from what the user has entered into the interface into forms
acceptable by the data sources themselves.

Data sources which have xml or XQuery-able rdbms can take XQuery formats
while others have to take a reduced xml format.

How's this sound?

Cheers,
Tony. 


> -----Original Message-----
> From: Tony Linde [mailto:ael at star.le.ac.uk] 
> Sent: 18 February 2003 08:47
> To: 'voql'
> Subject: FW: Query message format
> 
> 
> 
> 
> -----Original Message-----
> From: Ray Plante [mailto:rplante at poplar.ncsa.uiuc.edu] 
> Sent: 17 February 2003 22:40
> To: Tony Linde
> Cc: 'Registry_Ivoa_List'
> Subject: Re: Query message format
> 
> 
> Hi Tony,
> 
> > I've just proposed to the AstroGrid group that we base the format of
> > messages containing queries (eg from client, portal or workflow 
> > component to registry or dataset) on the W3C XQuery standard:
> > 
> > Note that I'm not proposing XQuery as the Astronomical 
> Query Language
> > (ie something that an astronomer would type into a query processor) 
> > but as the format in which such a query would be passed from one 
> > component to another.
> 
> In my opinion, the most important requirement of the query 
> interchange 
> format is that it be easily converted into other forms.  When 
> distributing 
> queries to many queryable services, you want the service 
> implementer to be 
> able to leverage off of existing capabilities as much as 
> possible.  This
> 
> will mean converting the query into the form currently 
> supported by the 
> repository.  This could include
>    *  an SQL query to a relational database
>    *  an XML Query to an XML database
>    *  an ASU query to an ASU interface
>    *  an SIA query to an SIA interface
>    *  a JVO query to the JVO grid.  
> 
> The conversion is not just a matter of transforming the 
> syntax, of course.  
> To leverage these existing systems, it will also involve transforming 
> the metadata schema used in the query from some standard 
> schema (e.g. like 
> SIA's use of POS=...) into the schema supported by the local 
> database.  
> 
> In my mind, if you want a message to be easily converted into another 
> form, it should be in XML.  This allows one to develop XSL 
> stylesheets 
> to do the transformation.  (In fact, the XSL stylesheets 
> could be created 
> automatically from an XML-based configuration file.)  The 
> fact that an XML 
> Query itself is not XML makes it difficult to transform into 
> other forms.
> 
> Brian Thomas and Ed Shaya have been working on a white paper 
> (http://nvo.gsfc.nasa.gov/QueryMediator/) exploring a query framework 
> based on an XML-encoded query syntax which I think could meet the 
> requirement of easy conversion.  We hope to experiment with 
> this in the 
> coming months.  
> 
> The use of an XML-encoded query as a query interchange format 
> does not 
> preclude AstroGrid's use of XML Query as its interchange format, 
> particularly in the near-term.  The idea is that it would be 
> straightforward, in theory, to transform the XML-encoded query 
> into XML Query and thereby accept queries from "outside" AstroGrid.  
> 
> cheers,
> Ray
> 
> 
>