[MOBY-l] Re: [MOBY-dev] lease versus agent for registry updating
gordonp at ucalgary.ca
Tue Aug 16 09:51:08 EDT 2005
My CAN$0.02 :-)
> 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.
This turns into an issue with the protocol, we would need to require
(when you register a service) test cases that return predictable,
non-null value. This was discussed at the last MOBY meeting, but I
don't think anything came of it. Or am I wrong?
> 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.
Like you said, the two approches aren't so different, because fetching
the RDF from the server is a callback of sorts.
>Anyway, can you really not
>determine the start point of a web services call?
If there are proxies, multiple host names for a machine (e.g. the host
I'm on right now is www.visualgenomics.ca, moby.ucalgary.ca,
www.gcbioinformatics.ca, and about 6 other names), it can get complicated.
> 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.
True, but the mechanism to exchange a URL list could be simpler than
mirroring the entire registry, and is less subject to error propagation
(e.g. don't blindly copy a goof in the main mirror's database system
because it had network connectivity issues, fetch the RDF yourself) .
If we're lucky, people will try to outcompete each other creating the
most robust registry :-)
>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
Would we set a maximum lease? I'd probably give myself a 1 year lease
so that I wouldn't be bothered again. That doesn't make me check that
the service works throughout the year though. IMHO, having a test case
checked regularly is what really helps here, not the lease. A lease is
someone's word, a test case is action, and actions speak louder than
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