# Input/Output expressions

I/O expressions are used to process multiple input or output documents in a single map.

I/O expressions can be used to:

* Read from and write to multiple data sources.
* Specify the location from which the data should be read or to which it should be written.
* Switch to a different representation in a map.

These expressions are only allowed in elements that inherit from other structures.

The following examples illustrate some use cases for these expressions.

### In this section

* [Reading from multiple files](https://help.qlik.com/talend/en-US/data-mapper-user-guide/8.0-R2025-06/reading-from-multiple-files)
* [Writing to multiple files](https://help.qlik.com/talend/en-US/data-mapper-user-guide/8.0-R2025-06/writing-to-multiple-files)
* [Embedding multiple representations](https://help.qlik.com/talend/en-US/data-mapper-user-guide/8.0-R2025-06/embedding-multiple-representations)