I need programming examples and an explanation of how to update
secondary data sources in Infopath programmatically, with filters
applied based on a field, and then updating further fields on a form
based on these data sources.

In this particular form, one of the data source links is updated
automatically when the form is opened, and the user chooses the
relevant database Record ID through a drop down menu (field1).

After a choice has been made in field1, the form should then update
the other relevant secondary data sources (there are 2/3 more) but it
*must* filter the lookup querys based on the information in field1, as
the lookups are taking too long at the moment (thousands of records, a
number of fields being pulled in).

There are then a number of fields on the form which use information
from these other data sources - these must be updated automatically
when the relevant information has been collected from the data
sources.

Please note the database is Access.

Either well written instructions will do with programming examples
(commented well!), or optionally for a better tip a database/infopath
example uploaded here would be great.

Thanks!