>>>Maybe I didn't explain myself right. I want the child table FK to have an option of empty string. In order to do it and maintain RI the parent table must have a row with an empty string value in the field. And of course I don't want the user to change the value in this Parent table for row intentionally or by accident. So I will need to have this row but not to allow user to make a change (therefore) to hid it. One way I though it to have a column/field that identifies this record (e.g. REC_ID) but was hoping for a less-maintenance type approach.
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>>Why do you need an empty value in PK/FK? Will this empty PK mean "other" ?
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>>Also, why you're allowing the users to deal with the Keys?
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>We talked about that before; I don't want to start this all over. This is not a surrogate PK but a user-specified.

If your front-end check if the value is empty and make this textbox Readonly. You can do it also in When event assuming VFP application.