Slots

Video#

In Rasa, slots are your long term memory in a conversation. If there's any information you'd like to store for later use, you'd typically want to store it in a slot. It's important to understand that a slot is not the same thing as an entity. You could store any information in a slot, even if no entity has been detected. That said, it is very common to fill a slot value with an entity value.

If you want to define a slot, you'll need to define it in your domain.yml file. In general slots can be defined in two ways: using NLU or using a custom. If you're using entity extraction via NLU models then you could extract a slot via a configuration like:

entities:
  - destination

slots:
  destination:
    type: text
    influence_conversation: false
    mappings:
    - type: from_entity
      entity: destination

Alternatively, if you're using a custom action to set slots. This is discussed in the custom actions segment of this course.

Influencing the conversation#

You'll notice that in these configurations that we've added a influence_conversation tag. The reason is that slots can influence a story. You might have something like this in your stories.yml file.

stories:
- story: booking a flight ticket
   steps:
   - intent: book_a_ticket
   - slot_was_set:
     - destination: Toronto

If your slots are configured to influence the flow of the conversation, you have to include them in your training stories. These slot_was_set events will now be included as training data for the machine learning pipelines in your assistant. Note that you're able to declare multiple values for a slot in a story via the or-operator.

stories:
- story: booking a flight ticket
   steps:
   - intent: book_a_ticket
   - or:
    - slot_was_set:
      - destination: Toronto
    - slot_was_set:
      - destination: London

Slot Mappings#

Slot mappings allow you to define how each slot will be filled in. Slot mappings are applied after each user message. For example, let's say that we have an entity called entity_name that we only want to store in a slot if the intent of the user is make_transaction. Then we might configure our slot via;

entities:
  - entity_name

slots:
  destination:
    type: any
    mappings:
    - type: from_entity
      entity: entity_name
      intent: make_transaction

Alternatively, we might also declare that we only want to detect the slot value if the current intent is not check_transaction. That could be configured via:

entities:
  - entity_name

slots:
  destination:
    type: any
    mappings:
    - type: from_entity
      entity: entity_name
      not_intent: check_transaction

Slot mappings give you more control over when a slot is stored. This is great because it might prevent you from storing a value in a slot if the user is mentioning an entity out of context.

There are many different types of slot mappings. The most common ones are:

• intent: only applies the mapping when the intent is predicted
• not_intent: does not apply the mapping when the intent is predicted
• role: only applies the mapping when the extracted entity has a specific role
• group: only applies the mapping when the extracted entity belongs to a specific group

It's also good to know that there are different methods of extracting slots. It's not just entities that are supported.

from_text#

You can store the full text the user has message as a slot value. This is is done via the from_text slot mapping.

slots:
  slot_name:
    type: text
    mappings:
    - type: from_text

from_trigger_intent#

The from_trigger_intent mapping will fill a slot with a specific defined value if a form is activated by a user message with a specific intent.

slots:
  slot_name:
    type: any
    mappings:
    - type: from_trigger_intent
      value: some_value
      intent: intent_name

custom#

You can also use a custom action to set the slot value. If none of the predefined slot mappings fit your case, you can creat custom slot mappings using slot validation actions.

slots:
  slot_name:
    type: text
    mappings:
    - type: custom
      action: action_calculate_day_of_week

Types#

In Rasa, slots have types. This is useful, because certain types of information are better served as a number than a string of text.

Text Slots#

Slot type text can be used to store any text information. It can influence the conversation based on whether or not the slot has been set.

slots:
  destination:
    type: text
    influence_conversation: true

Boolean Slots#

Slot type boolean can be used to store information that can get the values True or False.

slots:
  authenticated:
    type: bool
    influence_conversation: true

Categorical Slots#

Slot type categorical can be used to store values that can get one of a predefined set of possible values.

slots:
  price_range:
    type: categorical
    values:
      - low
      - medium
      - high

Float Slots#

Slot type float can be used to store numerical values.

slots:
  radius:
    type: float
    min_value: 0
    max_value: 100

List Slots#

List slots can be used to store a list of values. When configured, only the presence of the slot can have influence on the flow of the conversation. The values themselves won't be taken into account.

slots:
  items:
    type: list

'Any' Slots#

The "any" slot type can be used to store any arbitrary values. Slots of this type don’t have any influence on the conversation flow which means that the value and the presence of the slot doesn’t have any influence on how the conversation goes.

slots:
  shopping_items:
      type: any

Initial Values#

Finally, it's good to know that you can also set a default value on a slot by configuring the initial_value parameter. The value will be assigned to the slot from the beginning of the conversation and can be reset later on by NLU or custom actions.

slots:
  current_account:
      type: float
      initial_value: 100

Links#

• Rasa Slots Documentation

Exercises#

Try to answer the following questions to test your knowledge.

• When does a slot influence a conversation? When does it not?
• What's the difference between a slot and an entity?