Couple of questions on Understanding Devices Profile for Web Services, WS-Discovery, andSOAP-over-UDP

[Doug Davis <dug@us.ibm.com>]

Hi,
  I was reading Understanding Devices
Profile for Web Services, WS-Discovery, and SOAP-over-UDP and I had a couple
of questions:

1: Section 2 say:
       
The user decides to shut down the laptop. The laptop unsubscribes
itself from receiving event notifications from the printer. This is done
using WS-Eventing.
Odds are just as likely that the laptop
will leave the network w/o getting a chance to unsubscribe.  So, the
subscription will probably timeout - if an expires was specified.  Is
there some guidance on what value the subscriber should use for Expires
on the subscribe or when an event sink should destroy a Subscription in
the case of infinite expires times?  When the first notification fails?
 What if there's a network burp and its lost - the laptop could still
be there but the event source terminated the subscription due to this burp?
 These might be questions best answered as requirements in DPWS, but
wasn't sure.

2:  In WS-Discovery - xaddrs is
an address/URI and not an EPR, why?  I'm wondering about the case
where a single endpoint is hosting multiple services behind it. In this
case they might all have the same address/URI but different reference parameters
to distinguish them. 

3:  In the printer example the
notification of the printer status is sent to everyone, not just the sender
of that one job (no filter on the subscribe).  Is this intended or
in a more real example will the subscribe contain the proper filter to
make sure we don't overload the network?

4: Section 4.2.1 says:
3. A Target Service (or Discovery
Proxy) should use the same WS-Addressing [address] and [reference parameters]
properties for all messages over all network interfaces. This allows a
Client to recognize a Target Service (or Discovery Proxy) when they share
multiple networks.

Does this mean that it needs to have
the same IP address for all networks that its on? That doesn't seem possible
to guarantee.  I would think that some other unique ID (perhaps as
part of the metadata) would be used to check identity/equality of devices.
 The other concern here is that no spec actually defines how to compare
EPRs - and its a very messy subject  :-)


Aside from those I found it a very easy
read.  Nice job.

thanks
-Doug
______________________________________________________
STSM  |  Web Services Architect  |  IBM Software Group
(919) 254-6905  |  IBM T/L 444-6905  |  dug@us.ibm.com