STA Data Model (c) Ibrahim Mohamed
The STA comes out with “The Five Rules” of a standard STA data model diagram for a common business process:
1. Forms (such as source documents) are used as the main source for modelling.
2. Each T is connected to at least one S or A.
3. Each S, T and A has its own primary key (and their own non-keys/other attributes). But, only T has foreign key/s. S and A should not hold any foreign key.
4. All relationships are either 1:1 or 1:N, except for “bag”.
5. “Bag” (the grid in the form) will create many-to-many (M:N) relationship. 3NF should not have M:N relationship, so need to add a new associative entity to break the M:N into two 1:N relationships. So “WHEN there is a bag, THEN create an associative entity”. This new entity does not have primary key, but will hold foreign keys (the primary keys of those M:N entities) and other related keys in the grid. Thus, those M:N entities will not take the foreign keys taken by the associative entity.
By using the above method (The Five Rules), the data modelling technique can bypass the normalisation and cardinality processes, following the REA data model fulfilment of the 3NF.
