Partial Evaluation of Queries
If a data source is unavailable, DISCO evaluates as much of the query as possible and returns another query.
Example :
Consider the following query run when person2 is unavailable:
select x.name
from x in person0, y in person1, z in person2
where x.name = y.name and y.name = z.name
Returns the following result (where t0 is person0 join person1) :
select w.name
from w in t0, z in person2
where w.name = z.name