---
title: "Introduction"
slug: "cql-intro"
updated: 2025-11-18T18:08:25Z
published: 2025-11-18T18:08:25Z
canonical: "docs.doc-know.com/cql-intro"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.doc-know.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

### Clinical Query Language (CQL)

The Dr. Know **Clinical Query Language** (**CQL**) is a concise, but comprehensive set of natural language **expressions** that can be used to retrieve clinical information from a connected patient.

When embedding these expressions within curated content (i.e. apps, storyboards), they will be replaced with the appropriate clinical information at runtime.

### How Query Expressions Work

Clinical query **expressions** are enclosed in **double curly braces** and composed of 3 parts:

![image.png](https://cdn.document360.io/84e9ea69-d7ee-46a4-a14f-453de3411633/Images/Documentation/image%2836%29.png)

| Part | Required | Description |
| --- | --- | --- |
| **Subject** | Yes | The **entity** to be returned from the clinical expression. |
| **Filters** | No | Used to filter or reduce the subject. Must appear **before** the subject. |
| **Decorators** | No | Modifies the results in some way. Must appear **after** the subject. |

Some subjects support both a **singular** and **plural** format. For example, the expression '**bmi vital**' will display the most recent BMI value, while '**bmi vitals**' will return a list of all recorded BMI values.

Below is an example that returns the most recent 3 BMI vital sign values:

```
Prompt: {{ take 3 bmi vitals }}
Output: The most recent 3 BMI vital sign values.
```