xml-dev - XML-Data and database mapping

[Andy Dent <dent@oofile.com.au>]

I've been wrestling with issues for encoding databases (and report
definitions) into a single XML file and restoring them, for some time. I
would appreciate some feedback on the following. I would be ecstatic to be
told I'm blind, stupid, lazy and have missed some very obvious postings
covering all these issues :-)


-----
EMBEDDED SCHEMA

My current compromise is to have
<report>
   <Schema>
   </Schema>
   other tags
</report>

where the schema describes all following tags but obviously not the root
<report> tag.

Note: I'm using the MS convention of <Schema> rather than strict XML-Data
name <schema>.


-----
MAPPING FIELD TYPES AND TABLES

The most serious problem I see with mapping database schemae using XML-Data
or the other published suggestions is the lack of scoping.

As I understand the (suggested) specifications and the current MS versions,
fields within database tables will be handled by <ElementType> definitions
and referred to from within a table's <ElementType> by <element> tags.

This means that fields within tables are globally scoped in their
definition, unlike the usual DB practice that a field is defined within the
context of a database table (relation).

At a trivial level, "Name" might be a compatible data type such as
fixed-length string, but a different length, within <Person> and
<Organisation>.

I would vastly prefer to use an agreed standard for our schema
export/import but this restriction makes it impossible.

Once you accept that field definitions can be scoped within tables, it's a
much nicer syntax to define field data types within the <element> tag as
shown below. This approach can co-exist with defining <ElementTypes>
separately as separate definitions would be seen as
   <element id="#Address">
instead of
   <element name="Addresss" dt:dt="string">


-----
EXAMPLE OUTPUT

FWIW the following is the current output of our report writer, which I am
in the process of enhancing so it can read such a report document back in
again.

Note:
1) we encode layout separately from style

2) the style strings are mainly CSS compliant except if we have things like
graphs where we use CSS-like syntax to describe graph attributes

3) our layout has a CSS object model where possible and includes an
assumption of nested styles - an element within the layout inherits styles
from its containing elements.


<?xml version="1.0" standalone="yes"?>
<report>
<!--
     OOFILE extension to XML-Data allows <element> definition without
<ElementType> for primitives
     so our dbFields are <elements> with the datatype declared as
attribute, rather than the
     official method of declaring an <ElementType> then using an IDRef in
the type attribute
-->
   <Schema
      xmlns="urn:schema-microsoft-com:xml-data"
      xmlns:dt="urn:schema-microsoft-com:datatypes"
      xmlns:oof="urn:schema-oofile-com-au:datatypes">
      <ElementType name="perfTable">
         <element name="ID" dt:dt="string" oof:maxlen="15"/>
         <element name="Name" dt:dt="string" oof:maxlen="41"/>
         <element name="Awarded" dt:dt="ui4"/>
         <element name="Teacher" dt:dt="string" oof:maxlen="8"/>
      </ElementType>
   </Schema>
   <layout ID="1-1">
      <header>
         <box ID="1-1-1">
            <inline>Page 1</inline>
         </box>
         <box ID="1-1-1-2">
            <inline>Set your school name in &apos;Preferences&apos;</inline>
         </box>
         <box ID="1-1-1-3">
            <inline>Outcomes achieved by this student</inline>
            <inline></inline>
            <BR/>
            <inline>Josef ABRAMSON</inline>
         </box>
         <space height="4"/>
         <HR height="2"/>
         <space height="12"/>
      </header>
      <footer>
         <HR height="2"/>
         <space height="4"/>
         <box ID="1-1-1-3">
            <inline>KIDMAP 99 for Macintosh</inline>
            <inline>Printed by KIDMAP Manager on 5/5/1999</inline>
         </box>
      </footer>
      <table ID="1-1-1" source="perfTable">
         <footer>
            <space height="12"/>
            <box ID="1-1-1-1-2">
               <inline>Number of outcomes listed: </inline>
               <inline>24</inline>
            </box>
         </footer>
      </table>
   </layout>
   <style>
        #1-1-1{font-family: Helvetica; line-height: 1.000 ; font-size:  10
; color: rgb(0, 0, 0); text-align:  left}
        #1-1-1-2{font-family: Helvetica; line-height: 1.000 ; font-size:
16 ; font-weight: bold; font-stretch: expanded; color: rgb(0, 0, 0);
text-align:  left}
        #1-1-1-3{font-family: Helvetica; line-height: 1.000 ; font-size:
14 ; font-weight: bold; color: rgb(0, 0, 0); text-align:  left}
        #1-1-1-3{font-family: Helvetica; line-height: 1.000 ; font-size:
10 ; font-weight: bold; color: rgb(0, 0, 0); text-align:  left}
        #1-1-1{font-family: Helvetica; line-height: 1.000 ; font-size:  10
; color: rgb(0, 0, 0); text-align:  left}
        #1-1-1-1-2{font-family: Helvetica; line-height: 1.000 ; font-size:
12 ; font-weight: bold; color: rgb(0, 0, 0); text-align:  left}
   </style>
   <perfTable>
         <ID>ARDA11</ID>
         <Name>Draws upon play</Name>
         <Awarded>16th Mar 1999</Awarded>
         <Teacher>MANAGER</Teacher>
         <ID>ARDA21</ID>
         <Name>Use experience</Name>
         <Awarded>16th Mar 1999</Awarded>
         <Teacher>MANAGER</Teacher>
         <ID>ARDA31</ID>
         <Name>Explore ideas</Name>
         <Awarded>16th Mar 1999</Awarded>
         <Teacher>MANAGER</Teacher>
         <ID>ARDA41</ID>
         <Name>Experiment - ideas</Name>
         <Awarded>16th Mar 1999</Awarded>
         <Teacher>MANAGER</Teacher>
   </perfTable>
</report>

Andy Dent BSc MACS AACM, Software Designer, A.D. Software, Western Australia
OOFILE - Database, Reports, Graphs, GUI for c++ on Mac, Unix & Windows
PP2MFC - PowerPlant->MFC portability
http://www.oofile.com.au/

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