Decision Tree Overview

The tree app allows you to define decision trees that can perform a question-and-answer type interaction with a user. A tree consists of one or more states each of which is associated with a question and zero or more answers to that question that can transition to other states. As questions are answered the user traverses the tree based on the answers until he or she reaches a state that has no more transitions. At this point the user has completed the session. The tree saves every question/answer pairing in a single table, and provides functionality for applications to initiate a callback when trees are initiated and completed so that application developers can write their own processing of the tree data. A visualization of a tree is below.


Making a Tree

Currently trees can only be made through the admin interface.

Trees have a trigger, which is is the incoming message that will initiate a tree. They also have a root state which is the first state the tree will be in. The question linked to the root state will be the one that is sent when the tree is initiated. The remaining logic of the tree is encapsulated by the Transition objects, which define how answers to questions move from one state to the next (more on this below).

A tree also has optional completion text, which is the message that will be sent to the user when they reach a node in the tree with no possible transitions.


The behavior of a tree is fully encapsulated a set of states and transitions that define how one moves through the tree.

A Question is just some text to be sent to the user, and an optional error message if the question is not answered properly.

A TreeState is a location in a tree. A TreeState is associated with a Question (that will be asked when the user reaches that state in the Tree) and a set of Answers (Transitions) that allow traversal to other TreeStates.

A Transition is a way to move from one TreeState to another. A Transition has a beginning state, an Answer, and an optional ending state. If a transition has no ending state, the answer will result in the completion of the tree.

An Answer is a way to answer a question, and defines how one moves across a Transition

There are three possible types of answers:

1. The simplest is an exact answer. Messages will only match this answer if the text is exactly the same as the answer specified.

2. The second is a regular expression. In this case the system will run a regular expression over the message and match the answer if the regular expression matches.

3. The final type is custom logic. In this case the answer should be a special keyword that the application developer defines. The application developer can then register a function tied to this keyword with the tree app and the tree app will call that function to see if the answer should match. The function should return any value that maps to True if the answer is valid, otherwise any value that maps to False.

Registering a custom answer handler

The following code shows a function, and how to register that function with the Tree app as a custom answer handler for the word “demo”.

# inside myapp.App

def validate_password(self, msg):
    This function validates a password. This exact functionality could
    have been provided with a normal answer type, but you can put
    whatever logic you want here as long as you return True/False
    for matching/non-matching answers.
    return msg.text == "spomc"

def start(self):
    """Start is called by the router to bootstrap our app"""
    # get the app from the rapidsms router
    self.tree_app = self.router.get_app("tree")
    # register our validate password function with the "demo" keyword
    self.tree_app.register_custom_transition("demo", self.validate_password)


For emailed notifications associated with tags to work, INSTALLED_APPS must contain ‘rapidsms.contrib.scheduler’ and the setting DECISIONTREE_NOTIFICATIONS must be True. The default is False.


decisiontree can notice when it’s been waiting for a response for too long and send a reminder, repeating the question. This requires running celery and celerybeat, and the additional configuration in

On timeout, decisiontree will act as if it has received an invalid response. This results in sending a reminder and repeating the question, or, if the allowed retries are exhausted, giving up.