Scalable publish/subcribe with JavaSpaces ?

Hi,
I was just asking myself how the notify operation that was added to  
the JavaSpaces API (compared to the original set of operations  
available in the Linda tuple space) positions it to the publish/ 
subscribe paradigm.
One might think at the first sight that by introducing the notify  
operation into the space API a new communication paradigm is created  
that is more complex and more powerful than simple publish/subscribe.

However, the persistent nature of the shared data space has also a  
flip side.
The common task that is typical for all publish/subscribe services,  
namely simply the notification of all interested subscribers about an  
event, is very difficult to implemented in a scalable fashion.
Saving all notifications that occur in the space is usually not  
possible because most application scenarios involve so many  
notifications that the space will run out of memory.
The normal eviction functionality of tuple spaces cannot be used  
either to remove notifications. If the “time to live” property of a  
tuple is to short it might not get delivered to all interested  
subscribers, if it is too long the space could again run out of memory.

In order to handle huge amounts of notifications in a short time,  
each space would have to know the exact number of active subscribers  
for a notification in order to decide whether a notification can be  
removed safely.
This number however can change dynamically during the lifetime of a  
notification. Another approach would be to automatically delete a  
“notification tuple” after it has been matched to all templates that  
were active at the time the matching process began.
This behaviour would need a special treatment of “notification  
tuples”. The support for these “one-shot” tuples is as far as I  
understand not really part of the idea behind shared data spaces  
(namely using a share space to persist data)
   and would require a special space implementation.

I know that there are publish/subscribe implementations that are  
based on tuple spaces. For example GigaSpaces offers a JMS API.
I was wondering whether this is only possible by creating a new space  
implementation or whether it can be done with the current JavaSpace API.
  Note, that I'm talking about huge amounts of notifications that are  
published in a short time frame.
I think publish/subscribe with small or moderate notifcations rates  
should be realizable with the current JavaSpace implementation.

I really would like to hear your opinions and thoughts about this topic.

Best regards
Christian
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