How do you ensure that data is not altered/corrupted i

Hi Folks,

In certain domains loss of life may occur if data is altered/corrupted in any
way.

Suppose you write an XSLT program which transforms this:

<alt>12000 feet</alt>

to this:

<altitude>12000 feet</altitude>

How do you ensure that the data -- 12000 feet -- was not altered/corrupted in
the transformation?

I have heard of people doing a hash on the data prior to the transformation, a
hash on the data after the transformation, and then comparing the hashes. Is
that what you would do when lives are on the line? What is your
recommendation?

/Roger