允许任何具有定义前缀的属性

Question

I'm working on OFMX, an XML exchange format based on AIXM. The schema validates the publicly available files correctly, however, when OFMX is used internally, a number of attributes are inuse which are not part of the schema.

Here's a simple valid OFMX file:

<?xml version="1.0" encoding="UTF-8"?>
<OFMX-Snapshot xmlns:xsi="http://schema.openflightmaps.org/0/OFMX-Snapshot.xsd" version="0" origin="rubygem aixm-0.3.9" namespace="daf19610-f43b-4db3-80b7-602d9083dc32" created="2020-03-03T10:25:18+01:00" effective="2020-02-27T00:00:00+01:00">
  <Ahp source="LF|AD|AD-2.LFBA|2020-02-27|17">
    <AhpUid region="LF">
      <codeId>LFBA</codeId>
    </AhpUid>
    <OrgUid region="LF">
      <txtName>FRANCE</txtName>
    </OrgUid>
    <txtName>AGEN LA GARENNE</txtName>
    <codeIcao>LFBA</codeIcao>
    <codeType>AD</codeType>
    <geoLat>44.17472222N</geoLat>
    <geoLong>000.59055556E</geoLong>
    <codeDatum>WGE</codeDatum>
    <valElev>204</valElev>
    <uomDistVer>FT</uomDistVer>
    <valMagVar>0.0</valMagVar>
  </Ahp>
</OFMX-Snapshot>

In order to speed things up, non-public (local) processing might add attributes such as dbid :

<Ahp source="LF|AD|AD-2.LFBA|2020-02-27|17" dbid="1234">

I don't want to pollute the schema with such non-public attribute definitions and therefore I'm looking for a minimally invasive way to allow them.

Allowing any attribute with say a prefixed underscore like _dbid would be a solution, but AFAIK, it's not possible to define wildcard attributes in the schema.

Is there an alternative eg a local namespace like local:dbid maybe together with anyAttribute with as few modifications on the root element as possible?

Answer 1

The proper way to do this in XML is to put the attribute in a namespace, writing it as db:id="1234" with a namespace declaration for the db prefix.

The schema can then be written to permit either (a) any attribute in a specific namespace, or (b) any attribute in any namespace using an xs:anyAttribute wildcard with an appropriate namespace attribute, eg namespace="##other" .

If you want to make all your element declarations extensible in this way, the usual way is to derive all the element types by restriction from a type that contains the wildcard.