[MOBY-l] Re: [MOBY-dev] lease versus agent for registry updating

[Phillip Lord]

>>>>> "Paul" == Paul Gordon <gordonp at ucalgary.ca> writes:

  Paul> A few advantages of the lease are not really advantages in
  Paul> practice:

  Paul> 1. No one will manually update their lease, they will put it
  Paul>    in a cron
  Paul> job.  Therefore you either need to edit your crontab, or
  Paul> remove from the RDF file in the agent case.  Both are just as
  Paul> likely to be ignored by an administrator when a service stops
  Paul> working.


This is a necessary problem with neither the agent nor the lease. It
is a current problem with the implementation of the agent. All you do
is add a call back to the service. 


  Paul> 2. Specifiying that the service is valid for a certain amount
  Paul>    of time
  Paul> is mostly useful for testing purposes.  You should really be
  Paul> using a test registry in that case, not posting dubious
  Paul> services to the production server.

Not really. Take, for example, the SOAPLAB services Martin developed
as part of mygrid. When the toolkit was first produced, it was
deployed on our own servers; now it is supported by EBI's external
services. Clearly, the latter is likely to produce a better uptime
than the former. Hence, EBI might use a month long lease. 

Neither of these services were testing. But they did come with
different levels of support. 

  Paul> The chief advantages of the agent are:

  Paul> 1.  You can trace the registration and deregistration of a
  Paul>     service to
  Paul> a particular domain name.  It's not great security, but at the
  Paul> very least people require some serious work to pose as the
  Paul> NCBI on purpose (by hacking their Web domain), and cannot by
  Paul> mistake (e.g. "I registered my service using the NCBI
  Paul> authority ID because I'm using gi's").

Likewise with a lease call back system. Anyway, can you really not
determine the start point of a web services call? 


  Paul> 2.  The RDF for the services does not have a single point of
  Paul>     failure
  Paul> (i.e. the central registry).

This is also untrue. There is nothing to stop a lease percolating
through a set of federated registries. With the agent, you have to
percolate the registered URL's (or the RDF) in the same way. 

Ultimately, as two systems are doing similar things. It's just that
one is push and the other pull. 


  Paul> The one agent feature I would l;ike though is that I can call
  Paul> MOBY Central to tell it that I've changed my RDF, i.e. pushing
  Paul> a refresh. It's not critical though. If the agent runs once a
  Paul> day, you may get some latency on bad services, but it's not
  Paul> the end of the world.  Tim Berners-Lee got a lot of flack for
  Paul> his Web idea because it didn't enforce that what people linked
  Paul> to existed.  "People won't use it, they may end up at dead
  Paul> links!" they said...


You still want people to be able to search on the freshness of
information though. With a lease, you can add queries to moby-central
to say "give me only services with a current lease"--after all the
registry is not required to deregister a service when it's lease runs
out. 

Cheers

Phil