Modifiable rowsets

In V7 of Pyrrho I plan to have a more systematic approach to modifiable rowsets, which are useful in view-mediated data integration. Comments on the following proposals are welcome. Update: (12 April 2021) Working implementations of these ideas (alpha code) have now been posted to GitHub.

V7 uses immutable, shareable  rowsets (all typed values are also immutable and shareable). Compiled objects including table-valued functions and views have precompiled rowsets that are instantiated when accessed. Such instantiations are merged into the surrounding context, so that Pyrrho uses rowset review where other DBMS (and previous versions of Pyrrho) use query optimisation.

Some rowsets can be used to make changes to their base tables, and this feature is useful for views. As a rule of thumb this requires rowsets whose results expose simple rows and columns, possibly with a monotonic invertible adapter function, and thus all Yes entries in this table depend on this kind of additional requirement and the need to satisfy constraints and authorisation requirements. Such an operation adds to the transaction results a set of modifications for each of the individual tables involved. There are no entries below for rowsets with 0 or 1 base tables:

SubClass	Insert	Update	Delete
DistinctRowSet	No	No	No
DocArrayRowSet	Yes	Yes	Yes
EmptyRowSet
EvalRowSet	No	No	No
ExplicitRowSet
GroupingRowSet	No	No	Yes
IndexRowSet	(Yes)	(Yes)	(Yes)
JoinRowSet	Yes	Yes	Yes
MergeRowSet	Intersection only	Yes	Yes
OldTableRowSet
OrderedRowSet	Yes	Yes	Yes
RestRowSet	Yes	Yes	Yes
RoutineCallRowSet
RowSetSection	No	Yes	Yes
SelectRowSet	See below	See below	Yes
SelectedRowSet	Yes	Yes	Yes
SqlRowSet
SystemRowSet
TableRowSet	(Yes)	(Yes)	(Yes)
TransitionRowSet
TrivialRowSet
ValueRowSet
WindowRowSet	No	No	No

 It will be obvious in most cases what these RowSet classes are for. TransitionRowSet and OldTableRowSet are used in trigger implementation and are not directly accessible. A SelectRowSet has columns that are expressions, and only certain expressions are invertible to retrieve the underlying column values, while a SelectedRowSet picks and re-arranges columns from its source. RestRowSets are used in the implementation of RESTViews.