What characterizes a one-to-one relationship in database modeling?

To understand the characteristics of a one-to-one relationship in database modeling, it's essential to know that this type of relationship means that each instance of one entity corresponds to exactly one instance of another entity. This means that for each record in the first table, there is one and only one matching record in the second table.

The correct choice highlights that a one-to-one relationship involves a single instance for each entity. This means that two tables can relate directly to each other without duplicating records. For example, if you have a table for users and another table for user profiles, each user would have exactly one profile, and each profile would only be linked to one user. This one-to-one mapping ensures data integrity and eliminates redundancy.

In contrast to the incorrect choices, a one-to-one relationship does not involve splitting a logical entity across multiple physical entities, nor does it connect multiple entities directly or create infinite loops between entities. Each entity maintains its uniqueness and is clearly defined in relationships, thereby allowing for straightforward data handling and querying within the database structure.