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

# ConnectionValueTypeUndefined validation rule

> Validates that all connections have explicitly defined value types. Prevents ambiguous data model definitions that may cause issues when consuming data from CDF.

This rule checks that all connections have explicitly defined value types (i.e., end connection node type).

## Why it matters

If a connection value type is `None` (undefined), there is no type information about the end node of the connection.
This yields an ambiguous data model definition, which may lead to issues during consumption of data from CDF.

## Example

Consider a scenario where we have views `WindTurbine`, `ArrayCable`, and `Substation`. Let's say `WindTurbine` has a connection
`connectsTo` with value type `None` (undefined). It is unclear what type of view the connection points to, as
both `ArrayCable` and `Substation` are valid targets for the connection.

## Further reading

* [Validation rules](/cdf/deploy/neat/validation/index)