Ponyx is a web-application for explore ONIX data from PostgreSQL database.
Consider you have several ONIX messages in XML files:
# 20190806T081541Z.xml
<ONIXMessage xmlns="http://ns.editeur.org/onix/3.0/reference" release="3.0">
<Header>
<SentDateTime>20190806T081541Z</SentDateTime>
</Header>
<Product>
<RecordReference>1</RecordReference>
</Product>
<Product>
<RecordReference>2</RecordReference>
</Product>
...
</ONIXMessage>
# 20190807T081541Z.xml
<ONIXMessage xmlns="http://ns.editeur.org/onix/3.0/reference" release="3.0">
<Header>
<SentDateTime>20190807T081541Z</SentDateTime>
</Header>
<Product>
<RecordReference>1</RecordReference>
</Product>
<Product>
<RecordReference>2</RecordReference>
</Product>
...
</ONIXMessage>
...And you want to look at all the changes of the product with the reference 2.
Ponyx stores each ONIX message to the database table as xml column and then queries it with SQL and XPath to extract exactly what you want.