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Falko, what do you think of this?


Hi Falko,

I have to know what you think of the following:

A) We work with Gemstone in my shop; I was in charge of building a 
persistence framework on top of Gemstone, after we had tried to use de 
software as a plain-vanilla Java object cache (you take your object, you 
store it, period). The problem is we had many unexperienced developpers 
that did everything and anything with Gemstone, persisting this, persisting 
that. Chaos quickly arose from this... So I built a framework where 
developpers have to extend a given class, and use given collections. More 
precisely, we use tree-like objects - that have their own attributes, but 
that can also have collections of other objects. So we end-up with a 
tree-like object schema indeed, something really looking and feeling like 
XML, or, rather, typed XML per say, because we use objects with proper 
methods, not getAttribute(...) that returns a String.

Next thing I did was building a query language on top of the framework, 
that uses reflection to resolve the attribute names in the query string to 
the corresponding methods; here are example queries taken from the doc:

([departments[]/employees[]/])
Returns the list of all  employees in all deparments

([departments[name=$1]/employees[]/])
where $1=customer care
Returns the list of all employees in the customer care department

([departments[]/employees[age<$1 and age>$2]/])
where $1=25 and $2=45
Returns the list of all  employees below age 25 and above age 45

([payhistory[]/]) where key.emplKey in 
key([departments[name=$1]/employees[name=$1]/])
where $1=customer care and $2=Joe Johnson
Returns the list of all employees whose employee key corresponds to the 
employee(s) named Joe Johnson in the customer care department.

([departments[]/employees[age>$1 and [name!=$2 or name!=$3]]/])
where $1=25 $2=Joe Johnson and $3=Bob Bobson
Although this query does not make sense, it returns the list of emloyees 
whose age is greater than 25 AND whose name is not Joe Johson or Bob 
Bobson, in all departments  not that we have anything against these guys. 
This is just to show how nested criterium work: the query engine performs 
an AND (instersection) between two sets: the one for the age AND the one 
with the nested criterium.

([departments[]/employees[type.name=$1]/])
where $1=secretary
Returns the list of all  secretaries in all departments

This proved really useful, let me tell you. In really cut our development 
time and made our job fun. PLEASE DO NOT FLAME ME, I've read about your 
opinion on a query language for Ozone... I think, with all due respect, 
that this would be a great addition to Ozone (ok, now you'll say: why don't 
YOU do it then???). I know, I know, but I am already on the doc project, 
still assimilating what Ozone is all about... I do not dare pretend I know 
Ozone enough to do it, period. I'm a newbie.

B) How about notification built on top of JMS?

I mean, if a DB object is added/deleted/updated, it would be nice to be 
able to notify external listeners of theses changes - for synchronization 
purposes, replication, etc. Do you think a) this is a  nice concept; b) 
using JMS for it would be appropriate; c) this is what Ozone is about?

Anyway, sorry to disturb you. Hopefully you're not irritated...

Yanick.