[Chicago-talk] Decision tree code

Alan Mead amead2 at alanmead.org
Sat Feb 6 11:46:54 PST 2021

Maybe I'm stating the obvious, but if you don't want to change the code,
then you need to define the branching logic and questions/answers as
data and write an "engine" that processes the data and decides what
question is next based on the current state (e.g., the answer to the
current question, and possibly other information relevant to your
application). You should beware that this could become icky. For
example, it may be possible to create bugs in the branching logic.

I don't know what the context is, but I believe what you're describing
is called "skip logic" and "branching" in the survey industry and it's
implemented in packages like LimeSurvey: 

Even if you cannot use Lime Survey, you might look at how they implement
the rules and think about how you would build an engine to implement
this yourself. *I think in essence*, each question has an ID and the
survey has a sequence. Each item either has skip logic, or doesn't. If
skip logic exists for a question, then each response to the question
needs a ID to branch to. If not, the next question in the survey
sequence is chosen. It wouldn't be a monumental task to write this kind
of simple engine. I guess implicit in this is that you should be reading
your questions and answers from some kind of human- and machine-readable
format like YAML or JSON. This file is where you would insert the skip
logic in a format you devise. I found references to XPDL in googling as
described below. You should define as much complexity as you need. I had
a student who couldn't use SurveyMonkey because he wanted to administer
a six-item depression survey, score it, and then branch based on whether
the score indicated depression or not. At the time, scoring survey
questions and adding them up was beyond what SM could do. He found that
Qualtrics did have a feature to do this.

Implicit in my description above is that the main purpose is to collect
and store survey responses. If your goal is more like reaching a
decision (e.g., "Based on your responses, an adjustable-rate mortgage
would best suit your needs...") then the questions AND the ending
decisions have to be part of the data and perhaps the logic isn't as
simple as above (maybe there is no sequence and every question needs a
branch, or there are sections of questions that go together and branch
between sections). It looks like XPDL is an industry standard (in the
workflow industry)  for representing this.

If you google "decision tree" you get a bunch of hits for machine
learning. I googled "Perl decision process tree" and that lead me to
potentially useful articles like the one below, in which someone wants
to create flexible rules about "workflow" (how how tickets are routed in
a ticketing app): https://www.perlmonks.org/?node_id=222257

This is also similar to the way web frameworks work. But I think there
you'd be writing code to perform each step, so that's probably not helpful.

I am continually amazed by what's on CPAN but I doubt you will find a
module for anything like skip logic/workflow in abstract. I think it's
more likely to be embedded in a context, like the ticketing app, a
survey, or a web frame work. But it looks like there are some Perl
modules for implementing workfows.


On 2/6/2021 8:53 AM, Richard Reina wrote:
> I am trying to write code that would guide a user through a series of
> questions and depending on their answers given ask them different
> questions. I can of course do this with procedural code but it has
> occured to me that it might begin to get messy especially when
> exceptions mount. For example, if the answer to the third question is
> no, then skip to question 8. So I am looking for a way to structure
> such code to make it cleaner and perhaps easier to maintain, Does
> anyone know of any examples of similar projects that I can reference?
> Thanks,
> Richard 
> _______________________________________________
> Chicago-talk mailing list
> Chicago-talk at pm.org
> https://mail.pm.org/mailman/listinfo/chicago-talk


Alan D. Mead, Ph.D.
President, Talent Algorithms Inc.

science + technology = better workers


The irony of this ... is that the Internet is
both almost-infinitely expandable, while at the
same time constrained within its own pre-defined
box. And if that makes no sense to you, just
reflect on the existence of Facebook. We have
the vastness of the internet and yet billions
of people decided to spend most of them time
within a horribly designed, fake-news emporium
of a website that sucks every possible piece of
personal information out of you so it can sell it
to others. And they see nothing wrong with that.

-- Kieren McCarthy, commenting on why we are not 
                    all using IPv6

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