Steven:

As regards adding new records via the combo boxes it depends on whether the
text you enter in the combo box is the only data which needs to be entered,
other than an autonumber ID, or whether there are other columns in the table
which need to be entered.  In the first case you can do it all via the combo
box, in the latter case you normally need to open a form to enter the other
data, but possibly not in your case for reasons given below.

I'd imagine a new Category needs only the one value entered, i.e. the
category name, CategoryID being an autonumber.  In the case of a new
SubCategory you also need to enter the ID of the category of which the
sub-category is a part, but as you'll have already selected this in the first
combo box then you don't need to do the usual thing and open a form based on
the tblSubCategories table.

So the code for the category combo box's NotInList event procedure would be
along these lines:

   Dim cmd As ADODB.Command
   Dim ctrl As Control
   Dim strSQL As String, strMessage As String
   
   Set ctrl = Me.ActiveControl
   strMessage = "Add new category to list?"
   
   strSQL = "INSERT INTO tblCategories(Category) VALUES(""" & _
           NewData & """)"
   
   Set cmd = New ADODB.Command
   cmd.ActiveConnection = CurrentProject.Connection
   cmd.CommandType = adCmdText
   
   If MsgBox(strMessage, vbYesNo + vbQuestion) = vbYes Then
       cmd.CommandText = strSQL
       cmd.Execute
       Response = acDataErrAdded
   Else
       Response = acDataErrContinue
       ctrl.Undo
   End If

   Set cmd = Nothing

The code for the sub-categories combo box would be similar, but would extend
the SQL string so that values are inserted into both the SubCategory and
CategoryID columns, and would also confim that a category has first been
selected:

   Dim cmd As ADODB.Command
   Dim ctrl As Control
   Dim strSQL As String, strMessage As String
   
   Set ctrl = Me.ActiveControl
   If IsNull(Me.cboCategory) Then
       strMessage = "Please select a category first."
       Msgbox strMessage, vbExclamation, "Invalid Operation"
       Response = acDataErrContinue
       ctrl.Undo
   Else
       strMessage = "Add new sub-category of " & _
           Me.cboCategory,Column(1) & " to list?"
   
           strSQL = "INSERT INTO tblSubCategories(SubCategory,CategoryID) "
& _
               "VALUES(""" & NewData & ""," & Me.cboCategory & ")"
   
       Set cmd = New ADODB.Command
       cmd.ActiveConnection = CurrentProject.Connection
       cmd.CommandType = adCmdText
   
       If MsgBox(strMessage, vbYesNo + vbQuestion) = vbYes Then
           cmd.CommandText = strSQL
           cmd.Execute
           Response = acDataErrAdded
       Else
           Response = acDataErrContinue
           ctrl.Undo
       End If
       Set cmd = Nothing
   End If

As for the command buttons, frmAddNew is, as I understand it, an unbound
form with a bound subform within it.  Consequently, there can be no record to
save or delete in the parent from, only in the subform.  You could include
buttons in the subform's header or footer to save or delete rows from the
tblPublications table if the subform is in continuous form view, or in its
detail section if its in single form view.  If its in datasheet view then you
can use the built in menu commands or toolbar buttons. If you wanted to
delete rows from the categories or sub-categories tables via the Parent from,
then you'd need button's on the parent form which execute SQL DELETE
statements to delete the row for the category or sub-category selected in the
combo boxes, followed by requerying the combo boxes.  If, when you delete a
category you want all its sub-categories automatically deleted then you
should enforce cascade deletes in the relationship between the categories and
sub-categories tables.  Otherwise, assuming referential integrity is
enforced, as it should be, you would not be able to delete a category until
all of its sub-categories had been deleted.

To clear the Parent form just set the combo boxes to Null and requery
cboSubCategory:

   Me.cboCategory = Null
   Me.cboSubCategory = Null
   Me.cboSubcategory.Requery

This time it can be done from a button on the Parent form.  The subform
should then automatically show no publication records until a category and
sub-category is selected in the Parent form's combo boxes.

Finally one point I meant to mention in my first reply (apologies if I've
already said this in the past), but you seem to have a field for the author
in the tblPublications table, so it would not handle multiple authors for a
publication (which is common in scientific literature of course).  Also if
you don't have an Authors table which it can reference there is a strong risk
of inconsistent data creeping it; I have personal experience of this, having
encountered three versions of my own name as author in a table of technical
sources.  The relationship between publications and authors is potentially
many-to-many, i.e. each author might have written one or more publications,
and each publication might have one or more authors.  So you'd need a
PublicationAuthors table to model this, with PublicationID and AuthorID
foreign keys columns referencing the primary keys of the publications and
authors tables.  The effect of this on your form would be that you'd need
either a subform within the publications subform, if its in single form view,
or two correlated subforms within the Parent form if the publications subform
is in continuous form or datasheet view.  Either way the subform would be
based on the PublicationAuthors table.

Ken Sheridan
Stafford, England