As has been pointed out by Michelle Levesque in another post it is already possible for donor and recipients to cross reference each other and the IATI Standard does already make provision for that to happen. However, as Herman van Loon had mentioned (and it was also my understanding) I think that the original intention for traceability within IATI was just to trace upwards within the funding chain? Both Herman van Loon and Yohanna Loucheur have pointed out that a donor or funder can generally provide their own originating IATI activity identifier to the recipient via contract documentation and/ or as part of the contract management business process etc .
Interestingly, some of our most recent work within the Grand Bargain (particularly around issues relating to Localisation) is highlighting that there would indeed be value in being to be able to trace both ‘up’ and ‘down’ the funding chain. Presumably for this it happen, Donors and other funders would need to regularly ‘harvest’ the recipient activity identifiers and add them into their own systems. I think this process could certainly be automated and it would also provide donors with an automatic confirmation or validation that recipients have also now published the receipt of that funding to IATI? As a result I would be very interested to hear any views from donors or others on the practicalities and appetite (or lack of?) for making this happen?
Basically the process Andy Lulham describes, is deriving the downstream link. This is i.m.o. really an data use issue and not an IATI publication issue.
Publishing both links, increases the chance of introducing inconsistencies. Another reason against publishing both, is described above: at the moment the funder publishes the funding activity, the corresponding IATI identifier of the funded activity is usually not known.
So if you need the downstream link, derive it and use it in your application. But do not require to publish redundant data.
As far as the point matmaxgeds makes about secondary publishers: I would say this is one of the weaknesses and not strengths of IATI since secondary publishers obfuscate data ownership and introduce the same (but slightly altered?) IATI data of a primary publisher twice in the IATI ecosystem. What is the truth and who is accountable for data quality in that case?