Common Query Framework

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To support a range of Skills that can answer user's queries, each Common Query Skill must return a confidence score to indicate their ability to successfully complete the users request.
Introduction
The Common Query Framework handles the common use case of "general information" or question answering. Many Skills may implement handlers for "what is X" or "when did Y", the Common Query Framework allows all these Skills be queried and a single "best" answer to be selected. This is similar to the Common Play Framework that handles the common use of "playing" music or other media.
The Common Query Skill System is led by the Query Fallback Skill. This Skill handles queries matching a question pattern such as "What is the height of the Eiffle Tower" and "When is lunch". A matched question will be sent to all Skills based upon the CommonQuerySkill base class. The Skills will return wether they can answer the query along with an answer when applicable. The "best" match will be selected and spoken to the user.
CommonQuerySkill
A Skill interfacing with the Common Query Framework inherits from the the CommonQuerySkill and needs to define a method CQS_match_query_phrase() taking an utterance as argument.
The general structure is:
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from mycroft.skills.common_query_skill import CommonQuerySkill, CQSMatchLevel
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​
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class MyCommonQuerySkill(CommonQuerySkill):
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    def CQS_match_query_phrase(self, utt):
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       # Parsing implementation
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       # [...]
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       return (utt, CQSMatchLevel.LEVEL, answer_string)
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​
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def create_skill():
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    return MyCommonQuerySkill()
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The CQS_match_query_phrase() method will parse the utterance and determine if it can handle the query. if it can't answer it will return None and if it can answer it will return a data tuple with the format
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((str)Input Query, CQSMatchLevel, (str)Answer Text)
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The input query is returned to map the query to the answer.
CQSMatchLevel is an Enum with the possible values
CQSMatchLevel.EXACT: The Skill is very confident that it has the precise answer the user is looking for. There was a category match and a known entity is referenced.
CQSMatchLevel.CATEGORY: The Skill could determine that the type of question matches a category that the Skill is good at finding.
CQSMatchLevel.GENERAL: This Skill tries to answer all questions and found an answer. 
An Example
Let's make a simple Skill that tells us the age of the various Monty Python members. A quick draft looks like this. (You can find the complete code here)
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from mycroft.skills.common_query_skill import CommonQuerySkill, CQSMatchLevel
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​
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​
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​
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# Dict mapping python members to their age and whether they're alive or dead     
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PYTHONS = {
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    'eric idle': (77,'alive'),
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    'michael palin': (77, 'alive'),
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    'john cleese': (80, 'alive'),
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    'graham chapman': (48, 'dead'),
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    'terry gilliam': (79, 'alive'),
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    'terry jones': (77, 'dead')
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}
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​
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​
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def python_in_utt(utterance):
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    """Find a monty python member in the utterance.
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    Arguments:
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        utterance (str): Sentence to check for Monty Python members
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    Returns:
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        (str) name of Monty Python member or None
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    """
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    for key in PYTHONS:
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        if key in utterance.lower():
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            # Return the found python
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            return key
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​
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    # No python found
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    return None
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​
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​
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class PythonAgeSkill(CommonQuerySkill):
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    """A Skill for checking the age of the python crew."""
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​
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    def format_answer(self, python):
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        """Create string with answer for the specified "python" person."""
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        age, status = PYTHONS[python]
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        if status == 'alive':
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            return self.dialog_renderer.render('age_alive',
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                                               {'person': python, 'age': age})
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        else:
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            return self.dialog_renderer.render('age_dead',
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                                               {'person': python, 'age': age})
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​
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    def CQS_match_query_phrase(self, utt):
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        """Check the utterance if it is a question we can answer.
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​
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        Arguments:
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            utt: The question
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​
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        Returns: tuple (input utterance, match level, response sentence, extra)
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        """
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        # Check if this is an age query
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        age_query = self.voc_match(utt, 'age')
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​
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        # Check if a monty python member is mentioned
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        python = full_python_in_utt(utt)
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​
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        # If this is an age query and a monty python member is mentioned the
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        # skill can answer this
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        if age_query and python:
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            # return high confidence
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            return (utt, CQSMatchLevel.CATEGORY, self.format_answer(python))
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        else:
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            return None
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​
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​
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def create_skill():
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    return PythonAgeSkill()
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As seen above the CQS_match_query_phrase() checks if this is an age related utterance and if the utterance contains the name of a Monty Python member. If both criteria are met it returns a match with a CQSMatchLevel.CATEGORY confidence together with a rendered dialog containing the answer.
If both criteria are not fulfilled the method will return None indicating that it can't answer the query.
This will be able to provide answers to queries such as
"how old is Graham Chapman"
"what's Eric Idle's age"
To make this more exact we can add support for checking for the words "monty python", and if present return the highest confidence.
The method for parsing the example is quite simplistic but there are many different toolkits out there for doing the question parsing. Adapt, little questions, padaos and many more!
Better matching
If we want to make sure this Skill is used when the user explicitly states it's the age of a Monty Python member, a slight modification to the Skill can be made:
We'll change the end of the CQS_match_query_phrase() method to
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            if 'monty python' in utt.lower():
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                confidence = CQSMatchLevel.EXACT
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            else:
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                confidence = CQSMatchLevel.CATEGORY
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            # return high confidence
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            return (utt, confidence, self.format_answer(python))
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So if the utterance contains the phrase "monty python" the confidence will be set to CQSMatchLevel.EXACT making the Skill very very likely to be chosen to answer the query.
CQS_action()
In some cases the Skill should do additional operations when selected as the best match. It could be prepared for follow-up questions or show an image on the screen. The CQS_action() method allows for this, when a Skill is selected this method will be called.
The full signature is
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    def CQS_action(self, utt, data):
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where phrase is the same phrase that were sent to CQS_match_query_phrase() and data is optional additional data from the query matching method.
Example
Let's make our Python Age Skill gloat that it was selected by adding a CQS_action() method like this:
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    def CQS_action(self, utt, data):
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        self.log.info('I got selected! What you say about that Wolfram Alpha Skill!?!?')
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Now each time the Skill is called the above message will be added to the log! Not very useful you say? Hmm, yes... let's add something useful, like show the age on the Mark-1 display.
To accomplish this we need to get the age into the CQS_action() method in some way. we could store last age in as an internal variable but the more elegant way is to send data as part of the match tuple. To do this we must extend the returned match tuple from CQS_match_query_phrase() with a data entry. So the return statement becomes
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            data = {'age': PYTHONS[python], 'python': python}
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            return (utt, confidence, self.format_answer(python), data)
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The data structure declared here will be sent to the CQS_Action()method and we can update the method to
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    def CQS_action(self, utt, data):
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        self.log.info('I got selected! What you say about that Wolfram Alpha Skill!?!?')
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        age = data.get('age')
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        if age:
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            self.log.info('Showing the age {}'.format(age))
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            self.enclosure.mouth_text(str(age))
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