_____ completeness means that not every supertype occurrence is a member of a subtype.

I designed an entity relationship diagram (ERD) with the goal of creating two child entities (INSTITUTION and SPACECRAFT) of a parent entity (LOCATION), which is distinguished depending on the value of a boolean attribute (IS_SPACECRAFT). Implementing this in MongoDB, I'd like to link the INSTITUTION entity to another separate entity when IS_SPACECRAFT is false (0), and the SPACECRAFT entity to this other separate entity when IS_SPACECRAFT is true (1).

Right now, I am doing this manually by creating two attributes (SPACECRAFT_ID and INSTITUTION_ID) in this unrelated entity and pasting the object ID of either the INSTITUTION or SPACECRAFT entity in this attribute depending on the value of IS_SPACRECRAFT. But this inevitably leads to one of those attributes being NULL, which I think is poor database design and is something I'd like to avoid. With that in mind, is there a way to link another entity (i.e., as a foreign key) depending on a Boolean value in MongoDB?

Attached below is the ERD I mentioned earlier so the hierarchy is clear. The discriminator (d) is meant to represent a disjoint (overlapping) subtype, and the double lines represent a total completeness constraint, such that all the member of the parent LOCATION entity are in either SPACECRAFT or LOCATION, but not both.

For reference, a disjoint subtype is defined as:

Disjoint subtypes, also known as nonoverlapping subtypes, are subtypes that contain a unique subset of the supertype entity set; in other words, each entity instance of the supertype can appear in only one of the subtypes.

And total completeness is defined as:

The completeness constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype. The completeness constraint can be partial or total. Partial completeness means that not every supertype occurrence is a member of a sub-type; some supertype occurrences may not be members of any subtype. Total completeness means that every supertype occurrence must be a member of at least one subtype.

https://www.google.com/books/edition/Database_Systems_Design_Implementation_M/4JN4CgAAQBAJ

Chapter 05: Advanced Data Modeling

True / False

1. The entity supertype contains common characteristics, and the entity subtypes each contain their own unique

characteristics.

a. True

b. Fals

e

ANSWER: True

DIFFICULTY: Difficulty: Easy

REFERENCES: 5-1a Entity Supertypes and Subtypes

LEARNING OBJ

ECTIVES:

05.01 -

Describe the main extended entity relationship (EER) model constructs and

how they are represented in ERDs and EERDs

2. Entity supertypes and subtypes are organized in a specialization hierarchy.

a. True

b. Fals

e

ANSWER: True

DIFFICULTY: Difficulty: Easy

REFERENCES: 5-1b Specialization Hierarchy

LEARNING OBJ

ECTIVES:

05.01 -

Describe the main extended entity relationship (EER) model constructs and

how they are represented in ERDs and EERDs

3. The relationships depicted within the specialization hierarchy are sometimes described in terms of “is-a” relationships.

a. True

b. Fals

e

ANSWER: True

DIFFICULTY: Difficulty: Moderate

REFERENCES: 5-1b Specialization Hierarchy

LEARNING OBJ

ECTIVES:

05.01 -

Describe the main extended entity relationship (EER) model constructs and

how they are represented in ERDs and EERDs

4. Within a specialization hierarchy, a supertype can exist only within the context of a subtype.

a. True

b. Fals

e

ANSWER: False

DIFFICULTY: Difficulty: Easy

REFERENCES: 5-1b Specialization Hierarchy

LEARNING OBJ

ECTIVES:

05.01 -

Describe the main extended entity relationship (EER) model constructs and

how they are represented in ERDs and EERDs

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What are the types of completeness constraints?

What is completeness constraint?

What is an attribute in the supertype entity that determines to which subtype the supertype occurrence is related called?

When a supertype entity instance can be only one of its subtypes at a time the subtypes are called?