White paper on a strategy for full convergence of I/O and coupling tools (D2.5)

It has been recognised for a while that the main functions of I/O servers (like XIOS) and couplers (like OASIS), i.e. communication and transformation of data, have much in common. The question of “convergence” between XIOS and OASIS therefore naturally arises. In this document, we perform a technical analysis of the similarities and differences between XIOS and OASIS regarding their general architecture, specific functionalities, API, configuration and development resources. We then analyse advantages and disadvantages of such a convergence and propose a plan regarding this strategic question.
The analysis leads to the conclusions that 1) XIOS already contains most of the functionality required to act as a coupler and 2) that merging the two tools would not be a practical way forward as the effort of merging would be higher than the effort of extending XIOS. But at this point, the authors also state that it is too early to decide if we should encourage the climate modelling community to switch to XIOS for coupling as this functionality in XIOS is not fully developed, tested and validated yet. Only if the proposed steps, including more development and testing, are successfully achieved, we would then be confident that XIOS can be considered as a community coupler.