Re: Failure Modes and Ranges of Operation

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 03 Feb 2007 18:05:27 GMT
Message-ID: <H94xh.1948$R71.28470@ursa-nb00s0.nbnet.nb.ca>

paul c wrote:

> Bob Badour wrote:
>

>> paul c wrote:
>>
>>> Bob Badour wrote:
>>>
>>>> Neo's recent troll started me down a meandering path leading to 
>>>> these two separate but somewhat related (engineering) concerns.
>>>>
>>>> An operating range describes the conditions under which one of our 
>>>> devices will operate without failure. Failure modes are what happens 
>>>> when one tries to operate a device beyond that range.
>>>>
>>>> The sci.logic sort of folks grapple with the problems one encounters 
>>>> when one tries to have an infinite range of operation. And yet one 
>>>> can never fully escape the failure mode problem because division by 
>>>> zero generally fails.
>>>>
>>>> Failure mode analysis is very important in engineering. I wonder 
>>>> whether it has any supporting theory? Certainly, one can think of 
>>>> general principles. Likewise, beyond statistical analysis and 
>>>> empirical measurement, does any theory exist regarding ranges of 
>>>> operation?
>>>>
>>>> Any thoughts?
>>>
>>> Sorry, no theory here, just wondering if this question is the same as 
>>> asking whether relational closure is impossible when domains that 
>>> aren't closed under operators such division, are present?
>>
>> I assume you are suggesting that failures in extend expressions and 
>> restrict expressions cause extend and restrict to fail. Is that correct?

>
> Yes, I think that is partly what I was suggesting. Also, I don't think
> the RM is at fault for this (not saying anybody implied such), nor for
> the limits that come up when applying it on a finite computer.
>
> Whereas updating views seems to be an intrinsic, built-in kind of
> problem, eg., inserting to a union. I think I cannot rightly blame it
> on computers that are deterministic. In this case, I think Codd
> intended that some outputs, such as a multiple relation result for a
> single operator were out-of-bounds, even though the inputs might be legal.

You've lost me, Paul. What is the problem with updating a union view?

> If I think of all devices as having inputs and outputs (even a bridge
> that doesn't appear to move), such as air and fuel mixed in some
> proportion, it seems reasonable to not worry much about the times when
> somebody supplies an unacceptable input.

I suspect the pilot who flew beyond the fuel supply might disagree with you on that one.

   It's the combinations of
> inputs that produce unexpected outputs that then can't be used as inputs
> that puzzles me.

You've lost me again. Exactly what outputs are unexpected? Received on Sat Feb 03 2007 - 12:05:27 CST