[jibx-users] jibx design thoughts

Eitan Suez Mon, 07 Feb 2005 10:49:46 -0800

hi all,

  i've been philosophizing about jibx recently, trying to look
  at it from different angles..

  i'd like to share these thoughts because i believe i'm on
  an interesting path.

  topic:  jibx binding file definition

  statement:
   i find jibx to have one of the cleanest/simplest (and
   yet most powerful) binding file grammars

  i believe binding files can be very complex because they
  must do three things:
    1. define an xml structure
    2. define a java class structure
    3. relate how items in [1] relate to items in [2]

jibx does this very cleanly using common elements such as <mapping> <structure> <element> <value> and <collection> elements that are common to both the xml and java sides of things. yet on the other hand, the "name" attribute relates only to the xml side while attributes such as "field" and "class" relate only to the java side. to me, that's the essence of the flexible structure mapping that jibx allows.

  now, here are my thoughts:

    there already exist a number of xml languages for defining
    the xml structure:  xml schema, dtd's, relax NG, etc..

  jibx defines yet another grammar for defining the xml structure.
  i see this as a negative:  because programmers now must learn
  yet another grammar for defining an xml schema.

  thought:  why not piggyback on an existing grammar?
     suggestion:  Relax NG

  specifically, i think that jibx could be simplified if it defined
  only the java mapping aspect on top of Relax NG

  example:
   1. Java:
    class Customer {
      String _name;
      Address _address;
    }
    class Address {
      String _street, _city, _state, _zip;
    }

   2. xml:
<customer name="eitan">
 <address>
   <street>101 x</street>
   <city>Boston</city>
   <state>MA</state>
   <zip>12345</zip>
 </address>
</customer>

  3. jibx binding:
<binding>
 <mapping name="customer" class="Customer">
   <value name="name" field="_name" style="attribute" />
   <structure name="address" field="_address">
     <value name="street" field="_street" />
     <value name="city" field="_city" />
     <value name="state" field="_state" />
     <value name="zip" field="_zip" />
   </structure>
 </mapping>
</binding>

 4. Relax NG Grammar:
     <element name="customer">
       <attribute name="name" />
       <element name="address">
         <element name="street">
           <text />
         </element>
         <element name="city">
           <text />
         </element>
         <element name="state">
           <text />
         </element>
         <element name="zip">
           <text />
         </element>
       </element>
     </element>

5. possible combined Relax NG - JiBX binding definition:

structured mapping could work quite nicely with this as well:

 a. structured xml but flattened java:
    above, replace this:
       <element name="address" jibx:field="_address">
    with:
       <element name="address">
  (leave out the jibx:field attribute)

  b. flattened xml but structured java:

     <element name="customer" jibx:class="Customer">
       <attribute name="name" jibx:field="_name" />
       <jibx:structure field="_address">
         <element name="street" jibx:field="_street">
           <text />
         </element>
         <element name="city" jibx:field="_city">
           <text />
         </element>
         <element name="state" jibx:field="_state">
           <text />
         </element>
         <element name="zip" jibx:field="_zip">
           <text />
         </element>
       </jibx:structure>
     </element>

relax ng allows this. that is, it's a valid schema document, and the jibx binding is layered above it.

i know these examples are no way conclusive proof that it's possible to handle all mapping cases. how would collections be handled? id-idref? i'm sure there are many more questions.

  i'm just eager for feedback at this point.

again, the advantage i see here is being able to define bindings on top of an existing xml schema definition language instead of a new one: 1. this alleviates the programmer having to learn another schema language 2. in the likely event that an xml schema already exists, defining the jibx binding would be much less work: just layer the jibx mapping information right on top of it, in a non-intrusive way

  thought:  maybe jibx can be made to work with both Relax NG and the
   XML Schema specification?

  feedback?

thanks, eitan


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