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Re: Ozone object identity...



Matt Smith wrote:
> 
> I've been following this thread on and off, so forgive me if i'm out of
> line...
> 
> Wouldn't using a hardware id tie you into that one machine?  What if the
> machine was upgraded?  If you used a machine id such as its host name, then
> it is transparent what is behind it.  Could even be an Ozone cluster.  So
> long as it knows about the right objects, does it matter?  Do these issues
> exist in Versant?  How do they avoid them/get around them?
> 
> I'm sure there is a good reason for everything, but I am just curious (or
> ignorant?) as to why you need such a low level identifier.

No these are tough problems and so far nobody has really commented on
the issues of import/export and replication and other issues.

Are copies of objects the same object or a new object? 

If I export an XML representation, does the OID come along and then will
the OID comflict in your ozone server if you import the file?

I'm by no means an expect on random number generator but you have to
have a heck of a good method so my VM and your VM never produce the same
number. Here is how I understood the logic behind the composite three
number thing. If machines are unique which they are since they are true
objects then even if the object part is a sequencial thing 1,2,3 ...
then the combined OID (machine part + object part) is unique. But you
can also have more than one instance of Ozone running on the same box so
you need to take that into consideration as well which is why there is a
objectbase part as the second component.

The true GUID approach must take a seed and random generator in which n
streams never produce the same number even with numbers of object larger
than I can perceive.

I certainly don't know if this is needed but since a worked with Versant
for a couple of years I thought it might be applicable.

Eric


> > Eric Richardson wrote:
> >
> >
> > Michael Keuchen wrote:
> > >
> > >
> > > Remember that the identity can not be GEU in all cases, e.g.
> > > when using a local database or a RemoteDatabase in an intranet.
> > > The identity can store as many informations as possible about the
> > > object location, but global uniqueness is not ensured.
> >
> > Microsoft has an algorithm for DCOM I believe provides a GUID
> > (Globally
> > unique ID). Versant and their three part ID based on machine id +
> > objectbase id + object id claimed to be unique.
> > I think the three part scheme make alot of sense although I don't know
> > how to get the ethernet id in Java for the first part but we know that
> > ethernet id is unique otherwise TCP/IP wouldn't work. I discussed this
> > in another part oif this thread.
> >
> > Eric
> >