I don't know what CSA is, but I know what HVAC is, so I will use that as an
example of how a relationship between PROJNO in the projects table and PROJNO
in the HVAC table would work. Each project contains many cost items. For
HVAC the first record may be blowers (type, size, brand, etc.), the second
item may be ducts, the third item diffusers, and so forth. In other words,
each job would contain an itemized listing of HVAC expenses. If PROJNO in
the Projects table is 101, and if a one-to-many relationship is established
between Projects and HVAC, then when you enter a record in Projects you also
have the opportunity to enter related records in HVAC. You can see this in
the table (Access 2000 and above, I think) by the presence of a + sign next
to each record in Projects. Clicking the + sign will show you the fields in
HVAC. In actual use you would do this with a form and subform. You would
make a form based on Projects and another on HVAC. In form design view drag
the icon for the HVAC form onto the Projects form. When you enter a record
in the Projects table (via the form) you can enter related records (as many
as you need) in the HVAC table (via the subform). Each record created in
this way in the HVAC table will relate to one and only one record in the
Projects table.
If on the other hand the HVAC table contains options from which you must
choose, and if those options are available to other Projects as well, that is
another matter. For instance, if the HVAC table contains a listing of
components available to all projects, you do not want a one-to-many
relationship between the Projects table and the HVAC table. Or there could
be a third option, in which you select the item as described in the previous
paragraph, then enter quantity and current pricing, or something like that.
In either the second or third option you would need a separate table (let's
call it tblProjHVAC) to store either the primary key from the HVAC table, or
the actual values if they are subject to change (price information, for
instance).
One point here is that the CSA, ARCHITECTURAL, and HVAC tables (or
tblProjHVAC, tblProjCSA, and tblProjArch) all relate separately to the
Projects table, but do not relate to each other. For your purposes there is
no need to tie them together in a query. You may want to use queries for
other reasons such as sorting or criteria, but that is another matter.