FW: Semantics of Preconditions and Effects

I think there is a simple solution to Mithun's problem lurking in the
thread.
The customer of the loan service doesn't really want to know *why* their
loan was denied; the status of their credit rating is irrelevant. They just
want to know *if* it is denied or not.
The problem is, how do we tell this from the output? In other words, how do
we get from an output message to statements about the world.
 
The description of the loan service runs as follows:
 
Loan Service:
   1. output = "loan approved", if creditRating = good
   2. output = "loan denied", if creditRating = poor
 
The output "loan denied" is received.
 
The (situation calculus) semantics of the conditional effect tells us that
following the output, we are in a situation s where we know 'loan-denied'.
I think this licenses us to remove the scare quotes from "loan denied" and
to interpret the output as telling us about the state of the world - at
least in terms of what the customer can be said to know at this point. It
doesn't require reasoning about my credit rating.
 
knows(loan-denied,s)
 
Given that we can only know something that is in fact true, it surely
follows that my loan is denied in situation s.
 
loan-denied(s)
 
I'm actually restating Mithun's point that we can only  talk about things
that are directly represented in the output (or elsewhere in additional
post-conditions).
It is this fact that  may be used in subsequent conditions (e.g. to prevent
a denied application from going through), and the customer has sufficient
information to be able to reason correctly about the (negative) outcome.
 
As it says on the wall of many an English Pub, "Please do not ask for
credit, as a refusal often offends".
 
 Steve.

-----Original Message-----
From: Sheshagiri, Mithun [mailto:Mithun.Sheshagiri@hp.com]
Sent: Thursday, August 28, 2003 3:18 PM
To: 'Monika Solanki'; Sheshagiri, Mithun
Cc: daml-process@bbn.com; www-ws; 'steve.battle@hp.com'
Subject: RE: Semantics of Preconditions and Effects


 

-----Original Message-----
From: Monika Solanki [mailto:monika@dmu.ac.uk] 
Sent: Wednesday, August 27, 2003 5:59 PM
To: Sheshagiri, Mithun
Cc: daml-process@bbn.com; www-ws; 'steve.battle@hp.com'
Subject: Re: Semantics of Preconditions and Effects



Sheshagiri, Mithun wrote:



Since ceEffect points to owl:Thing, there is nothing that prevents you from
representing Knows(ISBN) as an effect. Also, it is useful to have a means by
which you can generate an effect which is also a precondition for some other
service.

This is precisely what I was aiming at.



 
I also had some doubts about the semantics of conditional O/Es.
 
Loan Service:
   1. output = "loan approved", if creditRating = good
   2. output = "loan denied", if creditRating = poor
 
If this were the advertised service and after execution of the service using
WSDL, I get my output as "loan denied". It is important to know the value of
CreditRating, since it could be used to determine the cause of  the
output:"loan denied" and a contingency plan can be worked out. There are 2
ways of finding the value of creditRating: make it part of the output
message or deduce it from the output.
At per current spec, the value of creditRating is not part of the WSDL
grounding (output message). Is it correct to deduce that my creditRating is
"poor" from the output "loan denied"? If this deduction is correct, then the
semantics is IFF.
 

I don't think so it is correct to deduce anything 
(a) if it is not specifiied explicitly in the output
(b) if it is not specified anywhere in the service ontology specification

As Sheila mentioned in one of the other emails that it may be possible that
a provider may not want to divulge the details abt loan denial. In such a
scenario, no deductions can be made. 
[Sheshagiri, Mithun] 
In this particular case, since the service provider did describe condition
creditRating as part of the service ontology, he/she does want the user to
know the the reason for loan denial/loan approval. 

Alternatively if the semantics is only an implication, 

I think it should be, atleast logically it makes sense.


is the following correct:
As part of the service description I make the following additional
statements:
3. output of Loan Service is disjointUnionOf  ("loan approved" and "loan
denied")

I think we do need to specify something like this 


4. "loan approved" owl:complementOf "loan denied"
5. So when I get the output "loan denied" can I say something like
output(loan denied) is equivalent to ¬output(loan approved)
6. From 1. (and assuming ¬good=poor), I have creditRating=poor 
 

This can be discussed further as Bijan has suggested in one of the other
emails


And if value of creditRating cannot be found by any means (explicit,
deduction or some other service), then is there a need for using
creditRating in describing th service? This problem could be solved by
sending the value of creditRating as part of the output.

Since nothing is mandatory in the specification currently, I guess it all
depends on the service provider, i.e. if he wants to send it as part of the
output
[Sheshagiri, Mithun] 
I guess what I am trying to say is that if a publisher of the service wants
to convey something than he/she should have the means to do so. If the Loan
Service provider adhered to current specs, the value of the condition cannot
be conveyed. Please correct me if I am wrong

 

mithun

http://www.cs.umbc.edu/~mits1 <http://www.cs.umbc.edu/%7Emits1> 
 

Any comments from other members appreciated

Cheers,

Monika


-----Original Message-----
From: Monika Solanki [ mailto:monika@dmu.ac.uk <mailto:monika@dmu.ac.uk> ] 
Sent: Wednesday, August 27, 2003 2:26 PM
To: daml-process@bbn.com <mailto:daml-process@bbn.com> ; www-ws
Subject: Semantics of Preconditions and Effects



Hi All,

I am trying to understand the semantics of preconditions and effects . In
one of the papers 

Narayanan, S. and McIlraith, S., "Simulation, Verification and Automated
Composition of Web Services", 

I found that preconditions for any service can also be modelled as knowledge
based apart from physical preconditions.For e.g: agent Knows(bookName) for a
service like LocateBook. I am interested in knowing whether agent can have
knowledge based effects as well for e.g: agent Knows(ISBN), especially for
information providing services.

Any thoughts appreciated.
  
Cheers,

Monika

-- 
**>><<**>><<**>><<**>><<**>><<**>><<**>><<** 
Monika Solanki
Software Technology Research Laboratory(STRL)
De Montfort University
Hawthorn building, H00.18 
The Gateway 
Leicester LE1 9BH, UK 

phone: +44 (0)116 250 6170 intern: 6170 
email: monika@dmu.ac.uk <mailto:monika@dmu.ac.uk>  
web: http://www.cse.dmu.ac.uk/~monika <http://www.cse.dmu.ac.uk/%7Emonika> 
**>><<**>><<**>><<**>><<**>><<**>><<**>><<**


-- 
**>><<**>><<**>><<**>><<**>><<**>><<**>><<** 
Monika Solanki
Software Technology Research Laboratory(STRL)
De Montfort University
Hawthorn building, H00.18 
The Gateway 
Leicester LE1 9BH, UK 

phone: +44 (0)116 250 6170 intern: 6170 
email: monika@dmu.ac.uk <mailto:monika@dmu.ac.uk>  
web: http://www.cse.dmu.ac.uk/~monika <http://www.cse.dmu.ac.uk/~monika> 
**>><<**>><<**>><<**>><<**>><<**>><<**>><<**