DP-900 Describe core data concepts Practice Question
Which TWO of the following are common characteristics of a NoSQL database?
⚠ Common exam trap
Test-takers frequently confuse 'flexible schema' with 'no schema at all' or mistakenly think NoSQL always supports strong ACID transactions, when in reality most NoSQL systems trade ACID for scalability and performance.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Flexible schema
Option A (Flexible schema) is correct because NoSQL databases such as document stores (MongoDB), key-value stores (Redis), and wide-column stores (Cassandra) do not enforce a fixed table schema, allowing each record to have different fields and structures. Option E (Horizontal scaling) is correct because NoSQL systems are designed to scale out by distributing data across many commodity nodes via sharding and partitioning, rather than scaling up on a single server. Option B (Normalized data storage) is incorrect because NoSQL databases typically denormalize data, embedding related data in a single document or row to avoid joins. Option C (Strong ACID transaction support) is incorrect as a general characteristic because many NoSQL databases follow BASE (Basically Available, Soft state, Eventual consistency) and offer only limited or eventual consistency, though some now add ACID features. Option D (Relational data model) is incorrect because NoSQL databases use non-relational models such as document, key-value, graph, or column-family, not tables with foreign-key relationships.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Flexible schema
Why this is correct
NoSQL databases store documents, key-value pairs, or graphs without a fixed relational schema, so each record may carry different fields. This satisfies the stem's requirement for a common characteristic: schema flexibility lets developers evolve data structures without migrations, unlike rigid tabular models in relational systems.
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Normalized data storage
Why it's wrong here
Normalisation removes redundancy through joins, which is a relational modelling technique; NoSQL stores typically denormalise or embed related data for partition-local reads. It is tempting because normalised schemas are standard in OLTP design, and would be correct for a relational database, but the question asks for NoSQL characteristics such as flexible schema and horizontal scaling.
- ✗
Strong ACID transaction support
Why it's wrong here
Strong ACID guarantees across multiple records are a hallmark of relational engines; most NoSQL stores offer only single-item or eventual consistency. It is tempting because some NewSQL and certain NoSQL products do provide ACID transactions, and that would be correct if the question asked about those specific engines, but it is not a common NoSQL characteristic.
- ✗
Relational data model
Why it's wrong here
A relational data model organises data into tables with fixed schemas and foreign-key relationships, which is the opposite of NoSQL's document, key-value, column-family or graph models. It is tempting because many NoSQL databases still expose tables or SQL-like query languages, and would be correct for a relational warehouse, but not for NoSQL characteristics.
- ✓
Horizontal scaling
Why this is correct
NoSQL databases are designed to scale out across many commodity servers, adding nodes to distribute load and data. This horizontal scaling satisfies the stem's requirement for a common NoSQL characteristic, unlike vertical scaling, which upgrades a single server's CPU, RAM or storage.
Go deeper
Related to this question
Learn chapter
Azure Table Storage and Blob Data
Key term
Column
A column is a vertical set of values in a database table that stores one specific type of attribute for every row.
Key term
Schema
A schema is a blueprint or logical structure that defines how data is organized, stored, and accessed in a database or information system.
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