In the relational model, how are relationships between two relations or tables typically implemented?

Introduction / Context:
In the relational model, data is stored in multiple tables rather than a single large table. To represent logical connections between these tables, designers use keys. Understanding how relationships are implemented at the schema level is essential for building correct and efficient databases. This question focuses on the standard mechanism for expressing relationships between tables in a relational database.

Given Data / Assumptions:

We have at least two relational tables that need to be related, such as a parent table and a child table.
One table has a primary key that uniquely identifies each of its rows.
The other table needs to refer to these rows in order to represent a relationship, such as orders belonging to a customer.
The relational database enforces integrity rules to ensure that these references remain valid.
We are using conventional terminology for primary keys, foreign keys, and candidate keys.

Concept / Approach:
A primary key uniquely identifies each row in a table. A foreign key is a column or set of columns in another table that stores values matching those of the primary key in the referenced table. This foreign key implements the relationship: each foreign key value points to a corresponding parent row. Composite keys and candidate keys are also important, but the specific mechanism for linking tables is the foreign key to primary key relationship. Determinants that are not keys are normally removed during normalization and are not the standard method for implementing relationships.

Step-by-Step Solution:
Step 1: Recall that primary keys provide unique identification for rows in a table and are the natural target for references from other tables. Step 2: Recall that foreign keys are defined in a child table and refer to primary keys in a parent table. They are the standard tool used to implement relationships such as one to many and many to one. Step 3: Compare this mechanism with the answer options. The option that refers to foreign keys that reference primary keys in related tables directly describes this standard relational technique. Step 4: Confirm that composite keys and candidate keys by themselves do not automatically establish relationships unless they are referenced as foreign keys elsewhere.

Verification / Alternative check:
Consider a database with a Customers table and an Orders table. Customers has a primary key CustomerId. Orders has a column CustomerId defined as a foreign key referencing Customers(CustomerId). Each order row contains a value for CustomerId that links it to a specific customer. This arrangement allows queries to join the two tables and retrieve all orders for a given customer. Without the foreign key, the relationship would not be explicitly represented or enforced by the database.

Why Other Options Are Wrong:
Composite keys can be used as primary keys or foreign keys, but simply having composite keys does not by itself implement relationships. They must be referenced as foreign keys in other tables.
Determinants that are not keys are typically a sign of poor design and can create anomalies. They are not the standard mechanism for relationships.
Candidate keys are potential primary keys, but unless they are actually used as foreign key targets and referenced by foreign keys, they do not automatically create relationships.

Common Pitfalls:
A common mistake is to store related information in one table without using proper foreign keys, relying only on matching values without enforceable constraints. This can lead to orphan records and inconsistent data. Another pitfall is forgetting to index foreign key columns, which can reduce query performance. Understanding and correctly defining foreign keys is a fundamental skill in relational database design.

Final Answer:
Relationships between tables in the relational model are typically implemented by using foreign keys that reference primary keys in related tables.