Re: Data Types

Sorry, should have checked. Just forwarded it as is. Here the content of the
attachment:

===================================

Vendor Specific Data Types



Essentially all DBMS's feature mutually incompatible extensions to SQL
types.
Encountering such data typesin real world deployments is inevitable.
Hence a generic RDB to RDF mapping needs to be able to deal with these.

The following are examples  of such types:

- XML - Most DBMS's have an XML data type and SQLX funcions.   In Oracle
these are handled like ú~ser defined types with the dot notation for
invoking methods like XSLT and XPATH.  In MS SQL Server the same
functionality is invoked via a function call syntax.


- User defined data types - Most DBMS's hhave user defined data types, i.e.
structures with named fields and methods.  There is usually a tree-like
inheritance system between types.  Method invocation usually looks like
Java, with  expression.method (arguments,....).


Geometries -  Some DBMS's have geometry data types more or less conforming
to the SQL MM and Open GIS specifications.  Oracle is close enough but not
quite conforming.  We note that there is a special spatial join syntax that
is not from SQL MM`, where  spatial joins are treated no differently from
other search conditions.



Generally, if one can define views and  table valued functions in the source
DBMS, these types may be decomposed into scalars.  However, the case where
the author of the mapping actually can create views on the source database
is a rare exception.

Furthermore, when translating SPARQL to SQL, a variety of target syntaxes
should be supported for  dealing with syntax variants, e.g. Oracle's and MS
SQL Server's  XML functions.

These are so divergent that a standardized meta language for the SPARQL to
SQL translation is a difficulty.

If SPARQL had 'fîlter ( xpath (?x, '//price',) > 10)
This would be col.xpath ('//price') > 10 in Oracle  where col is the
translation of ?x.

One could declare that a function-looking invocation became a method
invocation of its first argument.

Further, the Oracle spatial join as opposed to the equivalent SQL MM
expression is so different that an implementation must hard code  the
support.  The same applies to accessing table valued functions in general.
Most DBMS's have yjese in some form but details vary.

===================================

Cheers,
      Michael

-- 
Dr. Michael Hausenblas
LiDRC - Linked Data Research Centre
DERI - Digital Enterprise Research Institute
NUIG - National University of Ireland, Galway
Ireland, Europe
Tel. +353 91 495730
http://linkeddata.deri.ie/
http://sw-app.org/about.html



> From: ashok malhotra <ashok.malhotra@oracle.com>
> Organization: Oracle
> Reply-To: <ashok.malhotra@oracle.com>
> Date: Wed, 09 Jun 2010 05:20:00 -0700
> To: Michael Hausenblas <michael.hausenblas@deri.org>
> Cc: RDB2RDF WG <public-rdb2rdf-wg@w3.org>
> Subject: Re: FW: Data Types
> 
> I cannot read this.   Somehow, the linebreaks and formatting seem to
> have get lost.
> What tool did you use to read it?
> All the best, Ashok
> 
> 
> Michael Hausenblas wrote:
>> FYI.
>> 
>> Cheers,
>>       Michael
>> 
>>

Received on Wednesday, 9 June 2010 12:28:40 UTC