Please enable JavaScript.
Coggle requires JavaScript to display documents.
3-7 VALIDATING RELATIONSHIPS (RESOLUTION OF A M:M RELATIONSHIP (BARRED…
3-7 VALIDATING RELATIONSHIPS
RESOLUTION OF A M:M RELATIONSHIP
A
3rd entity
is needed to resolve the M:M relationship. This is called a
"intersection"
entity.
BARRED RELATIONSHIPS
The UID of the intersection entity comes from the
originating relationships
and is represented bars
M:M -> 2 1:M
COMPOSITE UNIQUE IDENTIFIER
UID that is a
combination
of attributes or
relationship
or
both
RECURSIVE RELATIONSHIPS
An
entity instance
is related to another instance in the same entity
Recursive M:M relationships contain an object that also has M:M relationship with other occurrences of the same object
Termed
BILL-OF-MATERIALS (BOM)
B'coz a
single
query makes any subpasses through the table to arrive at the solution
Can be resolve with an
intersection entity
ARC RELATIONSHIP
HELP
Arcs in data modeling
help
designers clarify an exclusive OR across relationship
XOR
A relationship between 1 entity and 2 (or more) other entities where only
one of the relationships can exist at a time
ARC
Always belong to
1 entity
Not all
relationships of an entity need to be included
Relationships must have the
same optionality
Represented as the arc-shaped line across 2 or more relationship lines
CONSTRAINT
= RESTRICTION on which attribute values and which relationships are allowed