Section 5
Relationship Nontransferable
A nontransferable relationship is represented with the diamond on the relationship
Redundant Relationships
A relationship that can be derived from another relationship
Intersection Entity
A third entity that is needed to resolve the M:M relationship; it will inherit a relationship to each entity from the original M:M
CRUD Analysis
An acronym for create, retrieve, update, delete. Helps you check for scope and completeness. If you have entities that are not touched by any CRUD function, then it might not be needed in the model. If you have a business rule with no entity to analyze CRUD with, then model might be incomplete.
Many-to-Many (M:M) Relationships
Crow's feet to crow's feet Common in the first version of an ER model but in the later stages of the modeling process, the relationships will be resolved and disappear
Relationship Transferability
If one entity can move to another entity, there is a relationship between the two that is transferable.
CRUD- Update
Look for words like CHANGE, MODIFY, ALTER, and UPDATE (Updating info that's already in the database)
CRUD- Delete
Look for words like DISCARD, REMOVE, TRASH, PURGE, and DELETE (deleting information that's already in the database)
CRUD- Create
Look for words like INPUT, ENTER, LOAD, IMPORT, RECORD, and CREATE (Indicate that a record is created in the database at this time)
CRUD- Retrieve
Look for words like VIEW, REPORT, BRING UP, PRINT, FIND, READ, and LOOK UP (Retrieving info that's already in the database)
One-to-One Relationships
Single toe to Single toe They will appear very few times. When roles are modeled, it is mandatory at one end. When a process is involved and the entities represent various stages in said process, the 1:1 relationship occurs.
One-to-Many (1:M) Relationships
The most common relationship; represented through solid/ dotted to crow's feet
Barred Relationships
The unique identifier of the intersection entity often comes from the originating relationships and is represented by the bars.