PLM — Intermediate Queries

The result of the concatenation of queries
is defined as the union of the result of the
single queries.

Some use cases needs another semantic of concatenated queries.
F.i. for the Start node identification use case
the set of Items selected by an Item_query
have to be filtered by an (optional)
following Item_version_query.
In this case the ItemQuery doesn't contribute directly to the
result of the whole concatenated query
but is only an intermediate step to define the start nodes
of the following Item_version_query.

To switch the semamtics of concatenation between

A) union of single result
B) intermediate step without contribution to the result
but with contribution to the start nodes of the next queries
a flag should be added to the class Query called "Intermediate".