[infod-wg] Notification in response to changes of Metadata - New Subscriptions

[Dieter Gawlick]

This is a first cut - will update as we go along


INFOD objects are managed in the INFOD registry by INFOD registry calls. 
It is assumed that the INFOD objects are stored as XML documents. 
However, data offered by publishers, processed by disseminators or 
consumed by consumers can be specified using any type system.

Subscriptions specify a series of selections. Some of these selections 
are associated to meta-data other are associated to the actual data. Let 
us first focus on the meta-data – which are represented in XML. A 
selection criterion is an (XQuery) expression against one or more 
collections of data. Examples of collections are publishers, 
associations, disseminator, and consumer.

Applying the relevant expressions to the collection of publishers, the 
INFOD registry will determine the requested publishers.

If there are limitations specified by publishers restricting subscribers 
the INFOD registry will check which publishers actually accept the 
subscriber of the current subscription.

More limitation may have to be checked; e.g., publisher may restrict 
consumers (or disseminators) and consumers may restrict publishers. We 
will skip this step for now – it seems to be and hopefully is 
‘straightforward’ using XQuery.

In the next step the part of the subscription that identifies which data 
are of interest needs to be processed. If the data source offers data in 
XML format and expression are XQuery based, the INFOD registry is able 
to determine whether the selection criterion is valid for that data 
source. If so, that data source will be notified and everything is set. 
The data source now begins to publish data according to the subscription.

Let us now assume that the data source has XML was some extension or not 
XML at all. In this case the INFOD registry is unable to check selection 
criteria for the data source. A vocabulary manager that is generic 
enough could either do this, in the absence of a vocabulary manager this 
can be done through a callback function to the publisher – we don’t have 
that interface – or by an acknowledgment/error message from the 
publisher – this again is not –yet – in the interface.

Once the publishers are identified the subscriber may get notified.

One could allow subscribers to verify and confirm selected publishers.

Whenever there is a change in any of the meta-data, all subscriptions 
have to be analyzed again and any new or dropped subscribers have to be 
informed as well as the subscriber.

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