Junction between categories

Question

I am making a database for a freelance sign language interpreter. I have a subject table tblClient which holds information regarding the freelancer's clients. There is a lookup table tlkClientClientType showing the various types of clients (categorized on condition -- deaf, deaf/blind, etc). There is also a table called tlkClientModality. In this table are the different types of sign language offered by the interpreter. You can pick the client's preferred modality from the Client table.

Now the tricky part. There are certain modalities (basically just flavors of sign language) that should not be available to pick if the client is a certain type. For example, you cannot use "regular" (visual) sign language with someone who is deaf/blind. This is because regular sign language depends on the person being able to see. Instead, one would use "Tactile ASL" which is a hand-over-hand version of sign language. Basically, I want to limit the modality list based on the client type picked.

To start off my associations, I am making a junction table between the tlkClientClientType and tlkClientModality tables. Here, I will create the correct allowable pairs of client types and modalities. In addition, there is not really a necessary "junction field" to justify this relationship. I am considering making a "dummy field" as a way to still justify such a relationship.

Later, in a form for the client, I will edit the row source query on the modality combo box to be dependent on the choice selected in the client type box. This would be accomplished by checking what records in the junction table match the choice in the client type combo box.

Am I on the right track here? Making a junction table between two lookup tables seems weird. Is there anything wrong with it?

Note -- I would like to stay away from VBA, but I am up to writing macros to accomplish these goals. Any thoughts would be appreciated.

A photo of the relationships is given below.

Relationshipsphoto

Answer 1

Keep your tables in whatever normal form works for your business case. Your choice just changes how the information is stored which means you have to change how you write your queries as the information may be located in a different place. I chose a many to many relationship between client and clienttype. You want to set the modality combobox contents from the client combobox. This is a problem of the view not the model hence we change the view and not the organization of the data. the key is to set the recordsource of the modality combobox from the afterupdate event of the client combobox. Showing the results first: if the client is deaf we get:

if the client is blind or blind and deaf we get:

Private Sub cmbClient_AfterUpdate()
Dim RegularASL As Integer: RegularASL = 1
Dim TactileASL As Integer: TactileASL = 2
Dim ClientID As Integer: ClientID = Me.cmbClient
If ClientisBlindandDeaf(ClientID) Then
cmbModality.RowSource = "SELECT * FROM tlkClientModality WHERE ClientModalityID = " & TactileASL
ElseIf isClientBlind(ClientID) Then
cmbModality.RowSource = "SELECT * FROM tlkClientModality WHERE ClientModalityID = " & TactileASL
Else
cmbModality.RowSource = "SELECT * FROM tlkClientModality WHERE ClientModalityID = " & RegularASL
End If
cmbModality.Requery 'reload cmbmodality data
Me.Refresh 'repaint cmbmodality
End Sub
Public Function isClientBlind(ClientID As Integer) As Boolean
'Get rid of * in names vba can't parse the *
Dim isblind: isblind = 2
Dim ClientClientTypeID As Variant 'allows null return type
ClientClientTypeID = DLookup("ClientClientTypeID", "tlkClientClientType", "ClientID = " & ClientID & " AND ClientTypeID = " & isblind)
If IsNull(ClientClientTypeID) Then
isClientBlind = False
Else
isClientBlind = True
End If
End Function
Public Function isClientDeaf(ClientID As Integer) As Boolean
Dim isdeaf: isdeaf = 1
Dim ClientClientTypeID As Variant 'allows null return type
ClientClientTypeID = DLookup("ClientClientTypeID", "tlkClientClientType", "ClientID = " & ClientID & " AND ClientTypeID = " & isdeaf)
If IsNull(ClientClientTypeID) Then
isClientDeaf = False
Else
isClientDeaf = True
End If
End Function

Public Function ClientisBlindandDeaf(ClientID As Integer) As Boolean
If isClientBlind(ClientID) And isClientDeaf(ClientID) Then
ClientisBlindandDeaf = True
Else
ClientisBlindandDeaf = False
End If
End Function

note: cmbModality is set up just like it is bound to the entire tlkModality table then the record source changes are used to filter it in effect.