Some background on this.
An example use case:
A Kafka-Fuseki connector which take data, patches or SPARQL updates from
a Kafka topic (that is, anything that can POSTed to a dataset). Kafka
messages have a header so there is a content-type header and the message
is sent into Fuseki dispatch.
This is CQRS style systems - event-sourcing - data mesh.
Kafka has state. A Fuseki can stop, then sync up when it starts, or have
a customized view of the overall event history or CQRS-style reliable
systems.
https://martinfowler.com/bliki/CQRS.html
https://martinfowler.com/eaaDev/EventSourcing.html
https://www.thoughtworks.com/en-gb/what-we-do/data-and-ai/data-mesh
Not all Fuseki installations want to have all the Kakfa client code (it
looks to be 5 Mbytes + extra dependencies but as you add features, more
jars are needed).
So the base issue is how to have plugins? And how do they find
information about the server and its configuration?
Jena system initialization works for getting extra jars to wire
themselves into the various registries. SHACL compact syntax wires
itself into the parser registry. Adding a new operation to Fuseki works
this way (see TestFusekiCustomOperation).
Jena system initialization does not provide a way for the code to
interact with building a server. For example, it can't (in any sensible
way) get to see the configuration before the server is built, nor do
addition assembler declarations in a configuration file get to run in
some defined way.
The Kafka-Fuseki connector needs configuration
* Need to know where the Kafka bootstrap server is
* Associate the Kafka topic with a dataset
* Have a state management area (to track the offsets processed)
That's an assembler. Ideally, it should, optionally, be possible to put
that in the Fuseki configuration file. Whether is it same-file or
separate-file is a convenience issue for operation.
That's just one example of a module. Modules could pick just certain
points and log system information, or add system control functionality.
By being in the server build lifecycle that can even add servlets or
servlet filters.
Fuseki modules are an extension point. A module implements an interface
that has call points for calls during Fuseki server building which
expose the server datastructures.
Andy
Yes - this is £job related work.
