Hello Michael,

On 1 April 2011 09:01, Michael Anstis <michael.anstis@gmail.com> wrote:
hehe, so I walked into this one with my eyes wide shut :)

Given it is only possible to define implicit logical AND's between field constraints within a decision table and given it is not possible to introduce complexity with parenthesis, is the immediate problem domain smaller than the more generalised discussion surrounding "otherwise" or "else"?

The first limitation can be overcome by converting multiple single field constraints on the same field to a single compound field constraint on the same field; thus:-

r1:   age > 14, age <= 28 (i.e. age > 14 && <= 28) becomes
rx:   age <= 14 || > 28

I wonder whether this problem cannot simply be resolved with application of DeMorgan's Theorems (something I know a little about from studying electronics as a student years ago).

Attaboy!
 

Unlike some commentators I am not an expert in first order logic, and therefore would appreciate guidance if people are willing to help.

Well, the point is that you can come up with pretty nasty constraints even without parentheses:

   a > $1 && != $2 && < $3    # implicit assumption: $1 < $2 < $3

Of course, de Morgan will help you here, too, but you'll have to develop some hefty symbolic expression handling.

If expressions E1, E2, are the combined logical expressions for some field from rules r1, r2,..., the "otherwise" condition is

¬ ( E1 || E2 || ... ) =
¬ E1 && ¬ E2 && ...

and you continue to apply de Morgan's laws to all Ei.

But what about the very natural constraint combination of two or more fields as in my age/income example?

Perhaps an entirely different approach should be considered, too. I'm thinking of a generic mechanism, which would have to gain control before any rule from a certain rule table is executed for another fact or set of facts. Then you could inspect all pending activations, and whenever you have one for a rule without an "otherwise" in a column it should discard any activations for the same fact set for rules with an "otherwise" in that column. I think this could be done from an agenda listener.

-W



 

Thanks,

Mike

On 1 April 2011 07:02, Wolfgang Laun <wolfgang.laun@gmail.com> wrote:
Michael,

My position is that an otherwise for a single column is likely to
cause trouble by misunderstandings. Especially the operators >, >=, <,
<= are likely to be used to separate intervals, as in
r1:   age > 14, age <= 28
r2:   age > 28, age <= 42

If you apply the proposed definition, the otherwise results in
rx:   age <= 14, age > 42
which is obviously never true.

You can construct similar blackouts with two different fields, e.g.
r1:   age > 60, income > 100000
r2:   age > 40, income > 80000

You will have to do an in-depth analysis of the AST resulting from the
condition definition resulting from rule table lines $n+2 and $n+3 in
order to get it right.

My opinion is: Don't do it unless you can do it right.

Cheers
Wolfgang

PS: I could provide a definition for otherwise with matches and
soundslike, but I'd rather not.


On 31 March 2011 21:25, Michael Anstis <michael.anstis@gmail.com> wrote:
> Hi,
>
> I'm adding support for "otherwise" to (for the time being) the guided
> decision table in Guvnor.
>
> The idea being if you set a cell to represent "otherwise" the generated rule
> is the opposite of the accumulation of the other cells; perhaps best
> explained with an example:-
>
> Person( name == )
> Mark
> Kris
> Geoffrey
> <otherwise>
>
> This would generate:-
>
> Person(name not in ("Mark", "Kris", "Geoffrey")
>
> Equals is the simple example, this is my thoughts for the other operators we
> might like to support:-
>
> != becomes "in (<list of the other cells' values)"
> < becomes ">= the maximum value of the other cells' values
>
> For example:-
>
> Person ( age < )
> 10
> 20
> 30
> <otherwise>
>
> Person ( age >= 30 )
>
> <= becomes "> the maximum value of the other cells' values
>> becomes "<= the minimum value of the other cells' values
>>= becomes "< the minimum value of the other cells' values
> "in" becomes "not in (<a list of all values contained in all the other
> cells' lists of values>)"
>
> For example:-
>
> Person ( name in )
> Jim, Jack
> Lisa, Jane, Paul
> <otherwise>
>
> Person ( name not in ("Jim", "Jack", "Lisa", "Jane", "Paul" ) )
>
> I'm not sure there is a simple solution for "matches" and "soundslike" but
> welcome advice, although a possibility might be to create a compound field
> constraint:-
>
> Person ( name soundslike )
> Fred
> Phil
>
> not Person ( name soundslike "Fred" || soundslike "Phil" )
>
>
> Would this be considered the most suitable approach?
>
> Inputs and thoughts welcome.
>
> Thanks,
>
> Mike
>
>
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