In the case of a relational database consisting of tables, columns, rows, keys and foreign keys
, the mapping can be done using the following principles :
The primary key becomes a foreign key
in a new entity.
Since the min-max cardinalities for PRESCRIPTION are (1,1), we need to include the primary keys of all other entities as foreign keys
in the scheme that represents PRESCRIPTION.
If an association involves a light-weight superclass, it may be pushed down to the subclasses resulting in multiple foreign keys
or a foreign key
which could point to multiple tables.
The UPDATE rule controls data modification such that a foreign key
value cannot be updated to a value that does not correspond to a primary key value in the parent table.
Because floating point numbers aren't precise, they should never be used as primary or foreign keys
to link tables.
2 Create primary key with auto-incrementing default value, create date/time field, create foreign key
field 3 Define and implement referential integrity for database (relationships in MS Access) 4 Create query to retrieve single field constrained by WHERE clause (set query "criteria" in MS Access Queries: Design View) 5 Create query to retrieve multiple fields constrained by WHERE clause (set query "criteria" in MS Access Queries: Design View), including computed value field (using MS Access DateDiff function).
Key and foreign key
constraints are represented by attribute grammars, adding semantic rules to schema grammars, to carry key and foreign key
values (to verify their properties).
In the ATTRIBUTES section, the user must insert all of the fields of a record with the exception of the foreign key
fields, specifying for each attribute: name, type and value.
The Room segment becomes a relational table, but must have the HNAME field added as a foreign key
to establish the one-to-many relationship between it and the Hotel segment and to fully identify the room, since room number is unique only within each hotel.
Defining a brand platform for France and foreign key
A common example of structure redundancy is the placement of a foreign key
into a relation.