Need an independent specification document
During the PaNOSC project, the search API has de facto been developed and specified at the same time by a single reference implementation. I believe this is not the appropriate approach in this case. We need multiple separate implementations: at least one for each metadata catalogue and one for the search portal. These implementations are developed in independent projects, but need to adhere to the same specification. If that specification is only implicitly defined by one of the implementations, it becomes unclear whether a particular behavior is intended to be the specification or whether it is simply a bug in that implementation. It will end up in declaring the bugs in the reference implementation to be features and to be the specification that all other implementations have to follow.
What we need instead, is a separate specification document that is maintained independently of any implementation. It needs to define at least the data model and the API calls with their parameters. We would need a well defined decision making process for updating that specification.