Generate Subject Headings from codes

As subject heading text is not mandatory, it is perfectly legit to provide only codes for your subjects leaving "Heading text" column empty:

But by adopting this practice, you may reduce the discoverability of your books and eBooks. Indeed, some search engines, bookstores and other online systems will produce better classification/indexation of your titles if you also provide headings.

ONIXEDIT provides a handy tool to do it easily and automatically:

Just open the ONIX file you want to process, select all the titles it contains (CTRL-A) and choose "Generate missing subject Headings from Codes" in the Onix menu. You can also find this option in the contextual menu that appears by right-clicking on the selected titles.