Hi Glen,
Sander already explained it very well, here an illustrative example which is available as part of the SAP HANA-optimized BI Content.
Not sure if you are aware of this content, but it actually provides you with data models that are aligned with the LSA++ architecture (Open ODS Layer, EDW Core Layer, Virtual Data Mart Layer - and also Corporate Memory).
Below is an example of the shipped content in the content area MM - Purchasing.
Here you can see that the Open ODS Layer does not necessarily need to have a persistence in BW, but it makes sense to persist the data e.g. if you use ODP based extraction without PSA and you distribute the data into more than one data targets (e.g. Reporting ADSOs) in the EDW Core Layer.
Example is the procurement document line items (data source 2LIS_02_ITM) and schedule line items (2LIS_02_SCL) that are used to load different targets, such as purchasing document data, principal agreements, and purchase order delivery data.
The definition of the advanced DSOs for the Open ODS Layer and for the Corporate Memory might be very similar, e.g. they are both field based and write optimized. But the purpose of the two ADSOs and the amount of data they store is different:
- The field based ADSOs in the Open ODS Layer (e.g. /IMO/O_PUR11) is used as kind of PSA replacement to distribute the data within BW to the different data targets, otherwise you would fetch all data first from the ODQ in the source system multiple times. Similar to a PSA you usually would delete the data from this DSO after the data was loaded succesfully into all data targets
- The field based corporate memory ADSO (e.g. /IMO/CMPUR11) stores the whole history of data and is only used e.g. to reconstruct data e.g. if a change to transformation rules in the EDW Core Layer is required. As the data is only required on in exceptional cases the data does not need to be hold in-memory. Therefore the flag "Inbound table as extended table" is turned on for this ADSO in the standard content.
All the best,
Andreas