The index data readers are used to extract index values from a file attachment and transfer them to the target fields of the field catalog. Depending on whether an input system reads in the index data in file form, the input system artificially creates a file attachment. In this way, index extraction can be carried out independently of the input system using the same logic.

In the case of an XML file that was read directly from the file system, this file attachment is used directly as the source for the XML index data reader, for example. In the case of a mail input system, an index.json file attachment is generated artificially, which contains the metadata of the email. The file attachment is processed via the JSON index data reader. The format and name under which such an index file attachment is generated can be found in the description of the respective input system or specialized index data reader.