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## New in 3.7

Flows are part of Rasa's new [Conversational AI with Language Models (CALM) approach](/content/docs/learn/concepts/calm/index.html) and available starting with version `3.7.0`.

## Overview

In [CALM](/content/docs/learn/concepts/calm/index.html), the business logic of your AI assistant is implemented as a set of flows. Each flow describes the logical steps your AI assistant uses to complete a task. It describes the information you need from the user, data you need to retrieve from an API or a database, and branching logic based on the information collected.

A flow in Rasa only describes the logic your assistant follows, not all the potential paths conversations can take. If you're used to designing AI assistants by creating flow charts of how conversations should go, you'll see that flows in Rasa are much simpler. Check out [Rasa Studio](/content/docs/studio/build/flow-building/introduction/index.html) to build flows with a web interface.

To get familiar with how flows work, follow the [tutorial](/content/docs/pro/tutorial/index.html). This page provides a reference of the format and properties of flows.

## Hello World

A Flow is defined using YAML syntax. Here is an example of a simple flow:

```yaml
flows:
  hello_world:
    description: A simple flow that greets the user
    steps:
      - action: utter_greet
```

## Flow Properties

A flow is defined using the following properties:

```yaml
flows:
  a_flow: # required id
    name: "A flow" # optional name
    description: "required description of what the flow does"
    always_include_in_prompt: false # optional boolean, defaults to false
    run_pattern_completed: true # optional boolean, defaults to true
    if: "condition" # optional flow guard
    nlu_trigger: # optional list of intents that can start a flow
     - intent: "starting_flow_intent"
    persisted_slots: [] # optional list of slots that should be persisted at the conversation level after the flow ends
    steps: [] # required list of steps
```

### Flow ID

The id is required and uniquely identifies the flow among all flows. It allows only alphanumeric characters, underscores, and hyphens, with the restriction that the first character cannot be a hyphen.

### Name

The `name` field is an optional human readable name for the flow.

### Description

The `description` field is a summary of the flow. It is required, and should describe what the flow does for the user. Writing a clear description is important, because it is used by the [Dialogue Understanding](/content/docs/learn/concepts/dialogue-understanding/index.html) component to decide when to start this flow.

### Always Include in Prompt

If `always_include_in_prompt` field is set to `true` and the [flow guard](/content/docs/reference/primitives/starting-flows/#flow-guards/index.html) defined in the `if` field evaluates to `true`, the flow will be [always be included in the prompt](/content/docs/reference/config/components/llm-command-generators/#retrieving-relevant-flows/index.html)

### NLU Trigger property

The `nlu_trigger` field is used to add [intents that can start the flow](/content/docs/reference/primitives/starting-flows/#nlu-trigger/index.html).

### Run Pattern Completed

The `run_pattern_completed` field is used to determine if the [`pattern_completed`](/content/docs/reference/primitives/patterns/#default-behavior/index.html) flow should be run when the conversation is finished.

### If property

The `if` field is used to add [flow guards](/content/docs/reference/primitives/starting-flows/#flow-guards/index.html).

### Persisted Slots

By default, slots set in a `collect` and `set_slot` step are reset when the flow ends. To change this behavior, you can add these slots to the `persisted_slots` field.

### Steps

The `steps` field is required and lists the flow steps. For details please refer to [Flow Steps](/content/docs/reference/primitives/flow-steps/index.html).

## Examples

### A basic flow with branching

```yaml
flows:
  basic_flow_with_branching:
    description: a flow with a branch
    steps:
      - action: utter_greet
      - collect: age
        next:
          - if: slots.age < 18
            then: too_young_step
          - else: old_enough_step
      - id: too_young_step
        action: utter_too_young
      - id: old_enough_step
        action: utter_old_enough
```

### Linking multiple flows

```yaml
flows:
  transfer_money:
    description: Send money to another individual
    steps:
      - collect: recipient_name
      - collect: amount_of_money
      - action: execute_transfer
      - action: utter_transfer_complete
      - link: collect_feedback

collect_feedback:
    description: Collect feedback from user on their experience talking to the assistant
    steps:
      - collect: ask_rating
      - action: utter_thankyou
```

### Embedding a flow inside another flow

```yaml
flows:
  collect_recipient_details:
    description: Details of a money transfer recipient should be collected here
    if: False
    steps:
      - collect: recipient_name
        description: Name of a recipient who should be sent money
      - collect: recipient_iban
        description: IBAN of a recipient who should be sent money.
      - collect: recipient_phone_number
        description: Phone number of a recipient who should be sent money.

add_recipient:
    description: User wants to add a new recipient for transferring money
    steps:
      - call: collect_recipient_details
      - action: add_new_recipient

transfer_money:
    description: User wants to transfer money to a new or existing recipient
    steps:
      - action: show_existing_recipients
      - collect: need_new_recipient
        next:
          - if: slots.need_new_recipient
            then:
              - call: add_recipient
                next: get_confirmation
          - else:
              - call: collect_recipient_details
                next: get_confirmation
      - id: get_confirmation
        collect: transfer_confirmation
        ask_before_filling: true
      - action: execute_transfer
```

### Optionally ask for information

```yaml
flows:
  purchase_dress:
    name: purchase dress
    description: present options to the user and purchase the dress
    steps:
      - collect: dress_type
      - collect: dress_size
      - collect: dress_color
        ask_before_filling: false
      - collect: dress_material
        ask_before_filling: false
        next:
          - if: slots.dress_material = "cotton"
            then:
              - action: action_present_cotton_dresses
                next: END
          - if: slots.dress_material = "silk"
            then:
              - action: action_present_silk_dresses
                next: END
          - else:
              - action: action_present_all_dresses
                next: END
```