What characterizes a Key-Value Database?

• A. A database that stores data in key-value pairs.
• B. A database that stores data in tables with foreign keys.
• C. A document store with JSON only.
• D. An in-memory cache that cannot persist data.

Answer: (B)

Key-value databases store data as a simple mapping where each item has a unique key and an associated value. Retrieval is fast because you fetch the value by its key, without needing to navigate rows, tables, or relationships. This model is typically schema-less, meaning you don’t define a fixed structure for the value; the value can be a simple piece of data or a more complex object, and the storage system focuses on efficient key-based access and scalability. Many key-value stores also support persistence on disk or hybrid in-memory/disk configurations, but the defining feature remains the direct key-to-value mapping.

The other descriptions point to different data models. Storing data in tables with foreign keys is the hallmark of a relational database with structured schemas and relationships. A document store with JSON describes a document-oriented model where data is stored as document-like structures and queried by document fields. An in-memory cache that cannot persist would not emphasize durable storage, which is not a universal trait of key-value stores themselves.