Re: [RT] Implementing Cocoon Blocks

[Stefano Mazzocchi]

On Sunday, Aug 31, 2003, at 15:04 Europe/Rome, Christian Haul wrote:

Stefano Mazzocchi wrote:
On Wednesday, Aug 27, 2003, at 11:35 Europe/Rome, Christian Haul 
wrote:
Which is the whole point of my mail. Don't use dependency ranges, use
metadata specifying capabilities and requirements for this.
I think you greatly underestimate the complexity of the approach you 
are proposing.
Last thing I want is to enter the ontology problem space.
There is absolutely no need to go the full way and I don't suggest to 
do it. A simple list of features that are matched 1:1 would be orders 
of magnitude more powerful than version numbers.

But in case I'm missing your point, please provide an explicit 
example.
Actually, I have already provided one:

<provides-features>
   <feature name="html-skin"/>
   <feature name="wml-skin"/>
</provides-features>
<dependencies>
   <block name="core" uri="core">
      <feature name="html-serializer"/>
   </block>
</dependencies>
This would be a very simple block that has little requirements and 
provides few features.

Let's look e.g. at the databases block. For ease of use, let's assume 
that any tag appearing beneath "provides-features" is a name of a 
feature and let's assume that features may have sub-features:

<provides-features>
   <esql>
      <stored-procedures/>
      <grouping/>
      <get-xml/>
      <get-clob/>
      <get-blob/>
   </esql>
   <sql-transformer>
      <stored-procedures/>
      <get-xml/>
      <get-clob/>
      <get-blob/>
   </sql-transformer>
   <db-actions>
      <add/>
      <update/>
      <delete/>
   </db-actions>
   <mod-actions>
      <add>
         <autoincrement>
            <oracle/>
            <informix/>
            <mysql/>
            <postgres/>
            <hsqldb/>
         </autoincrement>
      </add>
      <update/>
      <delete/>
      <query/>
   </mod-actions>
</provides-features>
Now, another block might require the following:

<dependencies>
   <block name="databases" uri="db">
   <!-- *this* block will refer to the block satisfying
        the requirements as "cob:db" -->
      <esql>
         <grouping/>
      </esql>
      <sql-transformer/>
   </block>
</dependencies>
Which is apparently compatible. Even without knowing the semantics of 
a feature "esql" hence without ontologies.

OK, this is more expensive than comparing to integers. OTOH this will 
occurr only once when a new block is registered.
I am afraid of going down this path because you are not taking into 
account:

 1) semantic collision
 2) increased development/maintenance complexity due to more granular 
dependendies

even providing a fully namespaced taxonomy, the amount of "topics" 
would grow rather quickly and would also get into the "keydata 
syndrome": what is a keydata for me might not be for you.

so, in order to depend on a block, you would not only need a 
dictionary, but a full thesaurus.

which, at the end, will end up being an ontology.

and this path scares me already too much to be willing to get into it.

--
Stefano.