OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help



   RE: Mechanics of mapping relational data into XML

[ Lists Home | Date Index | Thread Index ]
  • From: Joshua Allen <joshuaa@microsoft.com>
  • To: 'Kar Yan Ng' <kyng@nQuire.com>, 'Jerry Murray' <Jmurray@Ironplanet.com>,"'xml-dev@lists.xml.org'" <xml-dev@lists.xml.org>
  • Date: Tue, 11 Jul 2000 21:28:58 -0700

Title: RE: Mechanics of mapping relational data into XML
IBM have an XML Extender for DB2 (free download on alphaworks or developerworks),
and MS SQL Server allows selecting to XML using a specified schema or automatic
(e.g. SELECT * FROM authors FOR XML AUTO).  I am sure other vendors can do
this now, too.  Besides persisting the recordset object to XML (as in ADO mentioned
below) and querying to get XML back, there are plenty of other ways to get XML
from a relational database.  I can think of 5 or 10 at least..
In a more generic sense, I read the first part of the question to be something
like:  "Should I join data first, then produce XML, or should I produce XML, then
join?"  (oversimplified a bit..)
I think this is similar to the situation when doing a distributed join, and you want
to know what is "best"?  Should I:
1) Ship results from A to B, then join
2) Ship results from B to A, then join
3) Ship results from both A and B to client and then join
In fact, it depends on the query.  That is why distributed
cost-based query optimizers are still worth paying for.
IMHO, the same is true with XML -- sometimes one technique
makes sense, and sometimes another.  Even things like your
caching strategy can change which technique is "best" for
a given query.  In general, it is still quite fast to let the relational
engine do all of your work, then convert to XML after the fact.
However there are certainly cases where this is not true.
Another thing to note about the technique Kar Yan mentioned
below is that you can be fairly database-agnostic.  All of the
major databases out there seem to have different syntax for
returning XML directly, but ADO always returns a recordset, no
matter what database you use.  If you convert from ADO to
recordset, you can be programming-language agnostic and
database agnostic.  (If you need your code to run on platforms
other than Windows and can use pure Java, I am sure that
Java recordsets now have [or coming soon] ability to persist
to XML generically).
-----Original Message-----
From: Kar Yan Ng [mailto:kyng@nQuire.com]
Sent: Tuesday, July 11, 2000 8:35 PM
To: 'Jerry Murray'; 'xml-dev@lists.xml.org'
Subject: RE: Mechanics of mapping relational data into XML

Does this sound like the functionality provided by the MSPersist and MSDataShape data provider in Microsoft ADO 2.5?


Kar Yan

      -----Original Message-----
      From:   Jerry Murray [mailto:Jmurray@Ironplanet.com]
      Sent:   Tuesday, July 11, 2000 7:47 PM
      To:     'xml-dev@lists.xml.org'
      Subject:        Mechanics of mapping relational data into XML

      I would like to get some suggestions for the mechanics of mapping relational
      data into XML for situations where the mapping requires grouping of data.

      QUESTION:  When exporting relational data to XML, should:

              a)      the domain model grouping be done by SQL or Java code prior
      to creating XML data, or
              b)      should XML data be created for each table, then have an
      application parse  the "XML" table documents and write the new desired XML
              c)      or ... can transformations be performed (e.g. using
      something like RELAX) to go from the "XML" table documents to the final
      single XML document
              d)      or... are any tools available that already handle this


      Given a relational database with three tables:  x, y ,z

      Table x has product information -> one row for each product
              For example:
              product-id  |  product_name  |  product_manufacturer
              123             widget1         manufacturerX
              456             widget2         manufacturerY
      Table y has other product information -> one row for each product
              For example:
              product-id  |  product_type  |  product_class
              123             type1           classX
              456             type2           classY

      Table z has product category - attribute - value information -> multiple
      rows for each product
              For example:
              product-id  |  product_component |  component_attribute |
              123             cover                   material
              123             cover                   color           blue
              123             cover                   weight_oz       8
              123             base                    material
              123             base                    color           gray
              123             base                    weight_oz       6
              456             cover                   material
              456             cover                   color           blue
              456             cover                   weight_oz       4
              456             base                    material
              456             base                    color           gray
              456             base                    weight_oz       7


                              <cover material=plastic color="blue" weight_oz="8"
                              <base material=metal color="gray" weight_oz="6" />
                              <cover material=plastic color="blue" weight_oz="4"
                              <base material=metal color="gray" weight_oz="7" />




      Jerry Murray


News | XML in Industry | Calendar | XML Registry
Marketplace | Resources | MyXML.org | Sponsors | Privacy Statement

Copyright 2001 XML.org. This site is hosted by OASIS