# Definitions

Definitions allow you to reference blocks from within a service commissioning file. While they share similarities with parameters, definitions are designed for internal use only.

You can define values of any data type, including object types. These values can be referenced using the `!ref` or `!merge` functions.

## Example

In this example, we create a definition for default Modbus endpoint settings that we want to reference.

{% code lineNumbers="true" %}

```yaml
modbusEndpointDefaults:
  connectionId: !ref modbusConnection
  operation: subscribe
  interval: 1000
  address:
    fc: 3
    length: 2
```

{% endcode %}

When you reference this definition using `!ref modbusEndpointDefaults`, you get the following value:

{% code lineNumbers="true" %}

```yaml
connectionId: !ref modbusConnection
  operation: subscribe
  interval: 1000
  address:
    fc: 3
    length: 2
```

{% endcode %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.cybus.io/2-1-2/documentation/services/service-commissioning-files/definitions.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.