Hi, In followup to this query:
> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ron Price > Sent: 16 May 2008 22:38 > Subject: [gt-user] federated query across ogsa-dai and dcql resources > > Is it possible to do a federated query when some data services use OGSA-DAI and some use DCQL? > a message was sent directly to Ron as follows (copied here for archiving to the lists as Mike Jackson is not a member of the lists). I should add that another good place to ask these queries is the [EMAIL PROTECTED] mailing list. Cheers, neil -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. ---------- Forwarded message ---------- Date: Wed, 21 May 2008 10:54:19 +0100 (BST) From: Mike Jackson <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Cc: Mike Jackson <[EMAIL PROTECTED]>, [EMAIL PROTECTED] Subject: Re: FW: [gt-user] federated query across ogsa-dai and dcql resources Hi Ron, Your query was forwarded to me by a colleage - Neil Chue Hong - so I'll try to answer. We've never heard of CQL or DCQL until now. I see from the CaGrid Wiki (via Google) they're both XML-based query languges based on querying data with respect to its UML information model and are used to submit queries to data services. In theory it should be possible to run queries over federations of OGSA-DAI and DCQL services. You'd need some "layer" or components to manage this. In particular, there needs to be: -A common query language for the federated resources, or using an existing query language. I'll call this L. -A common data format for query results, or using an existing data format. I'll call this D. and components to: -Convert queries in L into OGSA-DAI workflows. -Convert queries in L into DCQL queries. -Submit OGSA-DAI workflows, representing queries, to OGSA-DAI data services. -Convert data from OGSA-DAI services into format D. -Submit DCQL queries to DCQL services. -Convert data from DCQL services into format D. -Join the data, expressed in format D, from the different services. i.e. -L-> Translator -DAI workflow-> DAI service <-> database <-D- Translator <-DAI response- Client -L-> Translator -DCQL-> DCQL service <-> database <-D- Translator -DCQL response- So basically, components to translate queries, submit queries, translate data and combine data. As I said, in theory it's possible. How much effort it would take in practice however would depend upon the ease of identifying the best choice for L and D above. OGSA-DAI would be one framework in which such a layer could be implemented since it is designed with the intent of accessing and integrating data from distributed heterogeneous databases. Another alternative would be to devise a DCQL compliant presentation layer (data service) for OGSA-DAI which could convert DCQL queries to OGSA-DAI workflows. This means that OGSA-DAI servers would be used identically to DCQL compliant services. i.e. -DCQL-> -DAI workflow-> DAI DCQL service DAI core <-> DB <-DAI response- <-DCQL response- Client -DCQL-> DCQL service <-> DB <-DCQL response- I hope these are clear. If you need any more information please ask. Likewise, it would be of interest to us if you could send more details as to what you have in mind, if you can. Cheers, mike
