# Mapping Output Specification

The **Mapping Output Specification** step is an output placeholder used inside a mapping *sub-transformation*.

Use this step to define where the parent transformation can read output rows from the sub-transformation.

You can think of it as a special output step that passes rows back to the parent transformation at runtime.

![Mapping Output Specification dialog](https://773338310-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FYwnJ6Fexn4LZwKRHghPK%2Fuploads%2Fgit-blob-e3edf6d6430b34434a472df773605bf6d034e9b8%2FPDI_TransStep_Mapping_Output_Specification.png?alt=media)

### When to use

Use **Mapping Output Specification** when your transformation is designed to be executed as a mapping (for example, from the [Mapping](https://docs.pentaho.com/pdia-data-integration/pdi-transformation-steps-reference-overview/mapping) step or the [Simple Mapping (sub-transformation)](https://docs.pentaho.com/pdia-data-integration/pdi-transformation-steps-reference-overview/simple-mapping-sub-transformation) step).

A sub-transformation can contain:

* One Mapping Output Specification step (common)
* Multiple Mapping Output Specification steps (multiple outputs)
* No Mapping Output Specification steps (no output)

### Options

| Option        | Description                                                           |
| ------------- | --------------------------------------------------------------------- |
| **Step name** | Name of the step. This name must be unique within the transformation. |