Hi Emmanuel,
Syclo xchange table should comply to standard structure, which consists of two key fields: MOBILE_APP, OBJKEY. For oData delta token use case, MOBILE_APP is probably some constant value, OBJKEY is a 100 chars field, which can be a concatenated value. For composite key, which is your example, it should be the concatenation of all 5 key fields for your object.
It is possible to have non-key extension fields in an xchange table, so you can store the key field values in the extension fields to make it easier during delta calculation. For example, for material document, we have a composite key MBLNR + MJAHR. So the OBJKEY field should be the concatenation of MBLNR+MJAHR. Then you can add extension fields MBLNR, MJAHR in the xchange table, which contains the value of the original field. i.e, material document 49000177/2015, so OBJKEY should have the value 00490001772015. Extension field MBLNR should have value 0049000177, MJAHR should have value 2015.
Also like to point out, eTag is intended for conflict detection during CUD, delta token is for read query, these are different use cases.
Hope this helps.
Jirong Wang