# Strong and Weak dependencies

[**Youtube**](https://youtu.be/jQeVVlqxjj8)

In the [**JOIN and WHERE section**](/features/data-lineage/join-and-where.md), we discussed displaying columns used in JOIN and WHERE clauses. But we wanted to go further :)

Even if columns are data sources, it makes sense to divide them into 2 categories: columns that are direct data sources and columns that only influence them.

For example:

```sql
SELECT
  ROUND(a, b)
FROM t
```

Here, column A is a direct data source, while B is not. B influences the result, but A is the primary source.

Another example:

```sql
SELECT
  CASE
    WHEN A IS NULL
      THEN B
    ELSE C 
  END
FROM t
```

Here, the value from A doesn't appear in the result but affects it.

At [**Dwh.dev**](https://dwh.dev/), we divided such dependencies into classes: **STRONG** and **WEAK**. We annotated all core functions to determine which argument belongs to which class. We also analyze CASE WHEN and other cases. You can disable any of these classes in the settings panel:

<figure><img src="/files/IzWWtkryjOv2M7731KOW" alt=""><figcaption><p>Weak dependencies</p></figcaption></figure>


---

# 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.dwh.dev/features/data-lineage/strong-and-weak-dependencies.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.