Hi Glen,
Further to the excellent replies of Andreas (on Feb 17, 2016 2:09 PM and Feb 19, 2016 11:05 AM) I would like to add some final remarks.
Implementing LSA++ has new aspects we have to deal with. An important one is less (in-memory) persistence. On the other hand, many classic LSA principles are still valid and we still have to use "common sense".
The function / service of Open ODS layer and Corporate Memory layer is totally different. That is why as a best practice, they should not be combined.
The function of Open ODS layer is facilitating the inbound daily data flow (i.e. data acquisition). With the ODP (Operational Data Provisioning) framework, PSA is optional. Therefore an aDSO (field-based and in extended memory) can be used if required (i.e. it is optional). Andreas explained it with the Purchasing example. Like before, inbound data should not be stored for a long term. PSA clean-up is normally done after an x number of data loads, e.g. max. one week. This way you keep the inbound data flow clean.
Corporate Memory has an entirely different function: long term storage of all extracted data. This is why in classic LSA, Corporate Memory is modeled as a "branch-out" data flow. It can be updated after peak-hours and it does not burden the daily data flow anymore. The aDSO (field-based and in extended memory) will grow steadily in the course of time. Only in exceptional / emergency cases it can be used to repair or reconstruct data in the daily data flow. Moreover, it is considered that the data is more safe if it is stored apart from the daily data flow.
To wrap up: Inbound ODS layer is optional. If it is used, then the data retention period is rather short (e.g. one week). It can either be modeled as PSA (w/o ODP) or a field-based aDSO (with ODP). Housekeeping should be performed on a regular basis so that the data volume stays very small.
Corporate Memory is loaded off peak hours as a branch-out data flow. It is modeled as a field-based aDSO and the full history of extracted data is stored. Consider it as a "BI life insurance", you hope you won't need it but in case you must be able to rely on it. That is why it should not be part of the daily data flow to avoid any risks.
Last but not least, thank you Glen for initiating such an interesting discussion and thank you Andreas for your valuable knowledge sharing.
Best regards,
Sander