In data warehousing, a star schema consists of:

A central fact table (containing measures such as sales, quantities, amounts)

Multiple surrounding dimension tables (such as date, product, customer, location)

A core characteristic of a star schema is that the dimension tables are denormalized:

Each dimension table is usually wide and contains descriptive attributes in a single table (rather than being broken into multiple normalized tables).

This design simplifies queries and improves performance for analytical workloads.

Why the other options are incorrect:

A. It has a tabular structure.All relational schemas (OLTP and OLAP) are tabular; this is not unique to star schemas.

B. It stores transactional data.Transactional data is typically stored in normalized OLTP relational databases, not in star schemas (which are optimized for analytics).

C. It stores unstructured data.Star schema is a structured relational design, not used for unstructured data (e.g., text blobs, images).

Therefore, the defining characteristic listed in the options is: It has denormalized dimension tables (D).

CompTIA Data+ Reference (concept alignment):

DA0-001 Exam Objectives – Data concepts and environments: schema design (star vs snowflake).

Common data warehousing references describe star schema as: fact table + denormalized dimension tables optimized for analytics.