We have removed from Sect 2.1 all but the first sentence of the following paragraph. It would be useful to add an Appendix describing a real life example and allow to discuss the various possible implementation strategies.
Complex frequency setups are possible in the same observation, as already mentioned in Sect. \ref{sec:specificities}. For instance, new multi-band receivers acquire simultaneously different frequency bands with different setups (bandwidth, max/min frequency, etc.). Moreover, modern digital backends allow the simultaneous acquisition of more than one spectral window (each with its spectral resolution) inside each receiver band. Such a complex observation should be properly represented in an ObsCore Table.
As an example: the new tri-band K-Q-W receiver being installed on board of the INAF radio telescopes observes simultaneously the K, Q and W frequency bands in the same observations. It can be coupled with a digital backend delivering {\it n} different spectral windows for each of the three observed bands. In this example, if the highest-granularity approach to ObsCore is applied, such a case would be described with $3n$ entries in a ``flat'' ObsCore Table. In case of broadband spectro-polarimetric observations, like the simultaneous study of many emission lines, $n$ may become large. Thus, such numerous ObsCore entries associated to the same dataset might make it difficult for a user to understand the observing setup. The possibility to adopt different levels of granularity in an ObsCore Table might be considered.
We have removed from Sect 2.1 all but the first sentence of the following paragraph. It would be useful to add an Appendix describing a real life example and allow to discuss the various possible implementation strategies.
Complex frequency setups are possible in the same observation, as already mentioned in Sect. \ref{sec:specificities}. For instance, new multi-band receivers acquire simultaneously different frequency bands with different setups (bandwidth, max/min frequency, etc.). Moreover, modern digital backends allow the simultaneous acquisition of more than one spectral window (each with its spectral resolution) inside each receiver band. Such a complex observation should be properly represented in an ObsCore Table. As an example: the new tri-band K-Q-W receiver being installed on board of the INAF radio telescopes observes simultaneously the K, Q and W frequency bands in the same observations. It can be coupled with a digital backend delivering {\it n} different spectral windows for each of the three observed bands. In this example, if the highest-granularity approach to ObsCore is applied, such a case would be described with $3n$ entries in a ``flat'' ObsCore Table. In case of broadband spectro-polarimetric observations, like the simultaneous study of many emission lines, $n$ may become large. Thus, such numerous ObsCore entries associated to the same dataset might make it difficult for a user to understand the observing setup. The possibility to adopt different levels of granularity in an ObsCore Table might be considered.