diff --git a/optimade.rst b/optimade.rst
index c852b384..6ba5509f 100644
--- a/optimade.rst
+++ b/optimade.rst
@@ -3533,6 +3533,12 @@ Calculations Entries
 --------------------
 
 The :entry:`calculations` entries have the properties described above in section `Properties Used by Multiple Entry Types`_.
+Related :entry:`files` entries specified as relationships (as described in section `Relationships`_) list files used or produced by a calculation.
+They MAY be defined as either input or output files by the :field:`role` field inside the :field:`meta` dictionary of the JSON:API resource identifier object.
+The allowed values are :val:`input` for input files and :val:`output` for output files.
+If the :field:`role` field is not provided or the value is set to :val:`null`, a default role SHOULD NOT be assumed.
+It is RECOMMENDED to order the output files in the list of calculation's relationships in a way that prioritizes the files most likely to contain details which could be used to automatically analyze the performed calculation.
+Such an approach minimizes the number of calculation output files that need to be analyzed to possibly identify the code, type and parameters of the performed calculation.
 
 References Entries
 ------------------