[configuration] Flattening trees

[Emmanuel Bourg <eb...@micropole-univers.com>]

Hi, last week I started playing with the Preferences API and a Windows 
configuration manipulating the registry through JNI. I had not 
experimented with hierarchical configurations before, this led me to a 
dumb question : what are we supposed to do when a key contains a dot ? 
Should we search the value in the sub nodes or get the first property in 
the current node matching the key ? This issue can be illustrated with 
the following XML configuration:

<a>
   <b>
     <c>value1</c>
   </b>
   <b.c>value2</b.c>
</a>

What's the key "a.b.c" supposed to return ? "value1" ? "value2" ? Or an 
array with both ?

A lot of configurations have a hierarchical structure : LDAP, JNDI, the 
windows registry, INI files (a tree a depth 1), XML files, the Avalon 
configuration API, the JDK 1.4 Preferences API. That makes me wonder if 
we aren't on the wrong track for a generic configuration API, 
[configuration] is Properties centric for historical reasons, should we 
keep trying to flatten hierarchical structures and make them look like a 
.properties file ? Should we change the Configuration interface to 
support hierarchical structures directly (and turn 
PropertiesConfiguration into a tree) ? Should we support both separately 
with an XPath like syntax to unify the keys ?

Emmanuel Bourg


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