There is two issue here.

First, if you set cascade deletes in the relationship window, then that is
#1 defining issue here.

If you delete a parent record, and have 5 related tables to that main
record, all of the child records in all of those tables will delete
automatically (assume you set the cascade deletes in eh relationship
window). These child records will delete even if you just delete  main
record in a query. In fact, the setup of the query WILL NOT EFFECT this
behaviours. they will all delete automatic. and, you can delete the main
record directly from the table, or delete his record in some query. So, it
how you setup the relationships.

yes, if you base table is the child record, and you join in other records,
even the parent table..deleting this record will NOT delete the main
record. However, you have to be carefully, since often when you drop in a
main table, the query builder flips what table is the "base" table (the
first table you dropped in).

It must mean that the form is based on the main table, and the child table
is joined in.

Well, you have to clarify what you mean by parent data. You have a form
bound to a query with 50 fields, but only place 2 fields on the form...this
issue would NOT effect the deleting. (so, the fact that you "display"
or not "display" parent data is not a issue here. If you mean *include*
in the query..that is a different matter. It would not matter if you include
1, or 50 fields, the defining issue would be did you include the table at
all in the query).

The bottom line is that if you delete a record, you are deleting that
record. if there is cascade deletes, then they are ALWAYS DONE.

So, the ONLY confusing part here is that is the form based on the child
record ONLY, or did we miss-match this, and the query is actually based on
the MAIN table (parent table), but we think it is a query that displays both
parent + child. As I said, most of the time when you build a query, you work
from the top most table down (so, if you join in 2, or even 6 tables...you
start at the top most).

Also, the direction in which you draw the join line will very much effect
this.

If you delete a main record, the overriding issue is if you setup the
relations, and have cascade delete...it will always cascade delete records
of what tables you include in the actual query....

However, if you build a query that is based on the child record, and
it joins in the parent record...you delete this record via that query,
then ONLY the child record will delete. It going to be how your
delete query looks. If you are finding that deleting this record
causes the parent record to delete, then the query is based
on that parent table, and you just wrong about what table the
query is based on.

Setting up your relationships correct is very important..and can a
reveal a large number of things about the design of the application.
What follows is a repost of mien
on this issue:

-------------

A left join means that a query will return the "parent" records when the
child table HAS NO correspond record.

So, if we have Customers, and Invoices tables, a left join would give us:

CustomerName     InvoiceNumber
AppleBee
Donought Shop     1234
Doughnut Shop     1344

Note how AppleBee does NOT yet have a invoice number in the invoices
table..but the query still returns the record. You have to use left joins
for lookup values when you drop in many tables (can't use standard joins in
this case).

So, with a left join, the corresponding child record DOES NOT have to exist.
Just think of "left" side can exist...but the right side does NOT have to !

A middle join, or so called inner join is the standard join, and BOTH tables
have to have a value for the join.  The above would produce:

CustomerName     InvoiceNumber
Dounought Shop     1234
Doughutn Ship         1344

So, in the above inner join, our customer name of Applebee does not show,
since that customer does NOT yet have a invoice record in the invoice table.

To make a left join, you drop in the tables (in the query builder, or the
relationship designer), and draw the join line to the appropriate filed
between each table. You then double click on the join line. You then click
on the join type button

You get three options:

   Only include rows where the joined fields from both tables are equal
    (this standard default inner join)

  Include ALL records from "Customers" and only those records from
"Invoices" where the joined fields are equal

  (this is our left join. So, our main table Customers will be returned in
this query, REGARDLESS if the child records (invoices in this example)
exist, or not!. This is left join

  Include ALL records from "Invoices" and only those records from
"Customers" where the joined fields are equal
   This sis obviously a right join....

For forms, and sub-forms, and related tables, left joins are quite
important.

If you look at the following screen shot, you can see that most relations
ships are this left join, and RI is enforced.

http://www.members.shaw.ca/AlbertKallal/Articles/PickSql/Appendex2.html

tblBgroup (booking group) for example may, or may not have payments made
(tblPayments). Thus, you can add a booking group, and NOT have to add child
records. However, full RI is enforced, and you can see the side ways 8
"omega" sign AND THE ARROW HEAD. The simple lookup fields are simply just a
arrow drawn, and no "1", or omega sign exists (tblPayments to tblHowpaid for
example is a simple lookup). It is GREAT that I can look at the ER diagram,
and instantly know if child records are required, or they are not!!

The tables that MUST have a child records can also clearly be seen. If you
go from the tblBgroup to the its parent table, you will see table
tblBooking. You can easily see that there is a 1 to many here also, but NO
ARROW head exists. Thus, when I create a booking, my designs will ALWAYS
ASSUME that a child records in tblBgroup (booking group) will exist (ie: I
must code, and assume that when I add a tblBooking records, my code also
assumes that a tblBGroup will also have to be added). In plain English this
means that when I make a booking (reservation), my code assumes that
you MUST have people in that booking. However, I most certainly allow
people to be booked, but not yet have made any payments. So, your
relationship(s) if done right should reflect the rules you as a developer
want to maintain. I should point out that a left join, or a standard
(inner join) both allow child records to NOT exist, but you still
should correctly set this relationship, since when it comes to making
reports, and writing code...I will know what my assumptions
were at the time (ie: do I HAVE to add those child records
for the software to function correctly. So, if I write code to
make a booking, all of my code thus assumes that people
are also to be added to the booking. Break that assuming
of mine, and likely my code will break).

So, the ER diagram can convey a lot about your designs. Down the road, I can
now look at that diagram, and when writing code, I will know if the design
can, and does assume if child records are required. If you look at that
table, it is VERY RARE that I require the child record. That application has
about 60 tables, and I think only 1 or 2 in the whole thing is NOT a left
join.  Hence, you most certainly should set the relation in the window for
future reference, and also it will help you when you create a query, or a
report.