Re: [Firebird-devel] XML Load/Dump Utility

[Todd F. <ta...@le...>]

I would make the following modification to your proposed representation:

<?xml version="1.0" encoding="UTF-8"?>
<database>
      <metadata>
        <table name="table1">
          <col name="COL1" type="type1"/>
          <col name="COL2" type="type2"/>
        </table>
        <table name="table2">
          <col name="COL1" type="type1"/>
          <col name="COL2" type="type2"/>
        </table>
      </metadata>
      <data table="table1>
          <row><COL1></COL1><COL2><![CDATA[binary data or otherwise 
necessary to escape data]]></COL2></row>
          <row><COL1></COL1></row>
          <row><COL1></COL1><COL2><![CDATA[]]></COL2></row>
          <row><COL1></COL1></row>
      </data>
</database>

* Nulls are easily handled by a missing column.
* Blobs can be delt with using CDATA, you might want to use this for 
text too although text might be just as well escaping.

The trade off I see with this format over what you had proposed earlier 
is that this format solves the above to issues, while
perhaps adding an additional cost in size by a facter of 2 times the 
length of each column name.  This is balanced in
my opinion by two factors:

1. XML can be compressed at least one inparticular libxml can read 
gzipped files. Meaning increased disk space is  really a mute point.
2. It is typically faster to process XML with fewer attributes.  
Attribute parsing tends to be slower then simple tag processing.

I would also use UTF-8 encoding over ASCII; doing should leave open the 
possiblity of your xml being used in many more locales.

-todd

p.s. Perhaps I missed somewhere, but what is the reason for representing 
the tables/data in the database in an xml format?  Just curious ;-)

Leyne, Sean wrote:

>Jim,
>
>  
>
>>My evolving XML schema looks like this:
>>
>>	<?xml version="1.0" encoding="US-ASCII"?>
>>	<database>
>>	   <metadata>
>>	      <table name="MESSAGES">
>>	         <column name="TRANS_NOTES" type="blob"/>
>>	         <column name="EXPLANATION" type="blob"/>
>>	         <column name="ACTION" type="blob"/>
>>	         <column name="TEXT" type="varchar" precision="118"/>
>>	         <column name="CODE" type="int"/>
>>	         <column name="FLAGS" type="smallint"/>
>>	         <column name="NUMBER" type="smallint"/>
>>	         <column name="FAC_CODE" type="smallint"/>
>>	         <column name="SYMBOL" type="varchar" precision="32"/>
>>	         <column name="ROUTINE" type="varchar" precision="32"/>
>>	         <column name="MODULE" type="varchar" precision="32"/>
>>	      </table>
>>	   </metadata>
>>	   <data>
>>	      <rows table="MESSAGES">
>>	         <row TEXT="Do you want to roll back your updates?"
>>CODE="10351" NUMBER="351" FAC_CODE="1" SYMBOL=""
>>ROUTINE="process_statement"/>
>>	         <row TEXT="gen_descriptor: dtype not recognized"
>>CODE="10352" NUMBER="352" FAC_CODE="1" ROUTINE="gen_descriptor"/>
>>	         <row TEXT="MOVQ_move: conversion not done" CODE="10047"
>>NUMBER="47" FAC_CODE="1"/>
>>	         <row TEXT="BLOB conversion is not supported"
>>    
>>
>CODE="10048"
>  
>
>>NUMBER="48" FAC_CODE="1" SYMBOL="" ROUTINE=""/>
>>	         <row TEXT="expected type" CODE="10000" NUMBER="0"
>>FAC_CODE="1"/>
>>	      </rows>
>>	   </data>
>>	</database>
>>
>>The key questions, I think, are how data is presented.  My starting
>>    
>>
>point
>  
>
>>is:
>>
>>*	A table row is represented as a single xml element
>>*	Each non-null column is presented by an xml attribute
>>    
>>
>
>The representation proposed is exactly how I define XML schemas -- not
>sure you'll think this is a good thing ;-)
>
>You will have a problem with large text/blob columns.  There is a size
>restriction for attribute items.
>
>I don't recall the size limit, off the top of my head.  I am
>investigating and will reply back.
>
>  
>
>>*	Null columns are not represented
>>*	No special casing of blob values are supported
>>*	Column attributes are based on JDBC definitions
>>    
>>
>
>
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