A key-value NoSQL database is designed around a simple data model consisting of a unique key paired with an associated value. The primary and most efficient method for data retrieval is a direct lookup using this unique key. The database is optimized for this specific operation, providing low-latency reads and writes by avoiding the overhead of complex query processing, relationship traversal, or full table scans. This model treats the value as an opaque blob, and access is predicated on knowing the key beforehand.

A. Using SQL queries is the primary mechanism for relational databases, not key-value stores, which typically use simple get/put/delete APIs.

C. Traversing relationships between nodes is the defining characteristic of a graph database, which models data as nodes and edges.

D. Scanning all documents is an inefficient access method, though possible. The primary access pattern in document stores is typically via an index or primary key, similar to a key-value store.

1. Oracle NoSQL Database Documentation: "Oracle NoSQL Database is a key-value database... In a key-value store, the application stores its data using a key. It can then retrieve the data from the store using that same key. The store itself does not care what the data is; it just stores it."

Source: Oracle NoSQL Database, Administrator's Guide, Release 23.1, Chapter 1, "Introduction to Oracle NoSQL Database".

2. Oracle Cloud Infrastructure Documentation: "The Oracle NoSQL Database Cloud Service is built upon the Oracle NoSQL Database, which uses a key-value data model... Applications use a key to retrieve an associated value. This direct key-based access ensures extremely low latency for read and write operations."

Source: Oracle Cloud Infrastructure Documentation, "Overview of NoSQL Database Cloud Service", Data Models section.

3. University Courseware: "The simplest NoSQL data store is the key-value store... The API for a key-value store is very simple: insert(key, value), fetch(key), update(key, value), and delete(key). The primary access is by the key."

Source: Stanford University, CS 245: Principles of Data-Intensive Systems, Lecture Notes on NoSQL Databases.