Description of five relationships of Er-studio

1. Identifying Relationship:1 to many.

The primary key of the parent entity is the foreign key (FK1) of the child entity, and FK1 is the primary key.

2. No identifying, mandatory relationship:1 to many.

The primary key of the parent entity is the foreign key (FK1) of the child entity, and the FK1 is not empty.

3. No identifying, optional relaotionship:1 to many.

The primary key of the parent entity is the foreign key (FK1) of the child entity, and FK1 can be empty.

4. One-to-one relationship:1 to 1.

The primary key of the parent entity is the foreign key (FK1) of the child entity, and FK1 can be empty.

5. Non-specific relationship: Many to many.

The parent entity and the child entity are many-to-many relationships. In fact ER studio will automatically generate an intermediate table.

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Identifying relationship: Need to provide a foreign key to another table as a joint primary key

Non-identifying Mandatory Relationship: Force foreign key

non-identifying Optional Relationship: Optional foreign key

One-to-one relationship non-specific: no special relationship

Word Explanation:

Identifying: identification;

Mandatory: An order, a compulsion, a duty

Optional: Optional, not obligatory, elective

Specific: Clear, exact, exhaustive

Determine whether a relationship is non-identifying or identifying as long as the primary key of the area molecule entity, see if need the parent entity's foreign key to common as the primary key, the need is identifying, If the child entity's own primary key is uniquely identifiable, it is non-identifying.