Database Reference
In-Depth Information
(
plural form of the table name
) then be associated with yet one or more other (
plural form
of the table name
)? For example, here's a question you might pose for the STAFF table:
Can a single staff member be associated with one or more other
staff members, and can any one of
those
staff members then be
associated with one or more other staff members?
An answer such as the following (or one very similar to it) indicates that the STAFF table
has a self-referencing many-to-many relationship:
Yes, a given staff member can manage several other staff mem-
bers, and any one of those folks can then supervise one or more
other staff members.
Onceyou'veidentifiedthe
type
ofself-referencingrelationshipthatexistsforthetable,you
indicate it in the table matrix as you would any other relationship.
Relationships will often differ from one perspective to the other, and you must know how
to determine what type of relationship officially exists between each pair of tables on the
matrix.Youmakethisdeterminationusingthefollowingsetofformulas;eachformulacor-
respondstoaparticularrelationshiptypedefinition.(I'veprovidedthedefinitionsasapoint
of reference.)
1:1 + 1:1 =
1:1
A pair of tables bears a
one-to-one
relationship when a single
record in the first table is related to
only one
record in the
second table, and a single record in the second table is related
to
only one
record in the first table.
1:N + 1:1 =
1:N
A
one-to-many
relationship exists between a pair of tables
when a single record in the first table can be related to one or
more records in the second table, but a single record in the
second table can be related to
only one
record in the first table.
1:N + 1:N =
M:N
A pair of tables bears a
many-to-many
relationship when a
single record in the first table can be related to one or more re-
cords in the second table
and
a single record in the second
table can be related to one or more records in the first table.
Here is the specific procedure you'll use to identify the official relationship between a pair
oftablesinthematrix.(Itincorporatestherelationshipformulasintheprecedinglist.)Let's
first look at a generic version of the procedure.
1.
Select a pair of tables and note the entry at the junction between the first table and
the second table.
