When both entities are mandatory, each entity becomes a table, and the key of either entity can appear in the other entity's table as a foreign key
. One of the entities in an optional relationship should contain the foreign key
of the other entity in its transformed table.
The L1 information stored at the meta-level permits the implicit definition of the domain-dependent database schema, including information about primary and foreign keys
. The persistence schema for this solution remains constant for every domain, easing the definition of the database schema used by the repository.
Indicate the primary key in each relation by underlining; and double-underline or italicize foreign keys
In this association, the table courses contains the primary key and plays the role "primary" and the table chapters containing the foreign key
plays the role "foreign".
The second case is presented below: Gene_Product Database: GeneProduct relation ID Symbol DBRef Species Int Primary Key Varchar2 Varchar2 Integer Foreign Key Foreign Key
Type Full_Name Varchar2 Char Genome Database: Genome relation Gene_ID Species CHR Strend Int Primary Key Int Foreign Key
Varchar2 Int Gene_Name Description Varchar2 Varchar2 Global Schema: Our proposed model ID Symbol Dbxref Species Type CHR Strend Description Full_Name Global Schema: [8, 13] ID Symbol Species Type Full_Name CHR Strend and Description DBxref
The relationship classes are designed to relate two entities based on the primary key and foreign key
If SSN is chosen as primary key, it must be included as a foreign key
in the Car-table in order to link a car to its owner.
That is, before a record containing a foreign key
can be written, the object of the reference must exist as the primary key of the target table.
One of my noticeboards is devoted to foreign key
The field or fields used to link to a primary key in another data table are known as foreign keys
and a foreign key
is any field(s) used in a relationship.
If E has its own primary key, then that is also the primary key of [Tau](E); the primary keys of the constituent entities should be added to [Tau](E) as foreign keys
. If not, then the primary key of [Tau](E) is the combination of the primary keys of the constituent entities; each component of the primary key is also a foreign key
referring to the relation from the appropriate entity.
He presents a notion of musical metaphor (according to him, this is expressed in syntactic incongruity, as when Beethoven introduces a foreign key
into a simple lyrical passage) without ever consulting the stylistic theorists or philosophers of metaphor; Ricoeur and Max Black, for example, are not mentioned.