DP-900 Describe core data concepts Practice Question
A company needs to store JSON documents that are frequently updated by multiple services. The solution must support indexing and querying by any property. Which Azure data service should they use?
⚠ Common exam trap
A common mix-up: candidates confuse Azure Blob Storage's ability to store JSON files (as blobs) with the ability to query them by property, overlooking the lack of native indexing and querying capabilities.
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
✓
Azure Cosmos DB
Azure Cosmos DB is a fully managed NoSQL database designed for JSON documents, offering native support for indexing every property automatically without requiring a predefined schema. Its multi-model API (including SQL API) allows querying by any property with low-latency reads and writes, making it ideal for services that frequently update JSON documents.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Azure Blob Storage
Why it's wrong here
Azure Blob Storage is an object store designed for unstructured binary data, so JSON files can be stored as blobs but are not natively queryable. Retrieving frequently accessed documents requires downloading and deserializing the entire blob in compute, and there is no automatic indexing of JSON properties. For frequent, query-driven access, a purpose-built document database is more appropriate than Blob Storage.
- ✗
Azure SQL Database
Why it's wrong here
Azure SQL Database is a relational database that enforces a predefined schema, so schema-less JSON documents would have to be stored as text in columns. Although SQL Server's JSON functions and computed columns can simulate some flexibility, each JSON property must be explicitly mapped and indexed, and the engine does not automatically index arbitrary properties. This makes it operationally heavy for frequently changing JSON documents.
- ✓
Azure Cosmos DB
Why this is correct
Azure Cosmos DB is a fully managed, horizontally scalable NoSQL database that stores documents natively in JSON format and automatically indexes every property without requiring a schema. Its SQL API supports filtering, projection, and joins over JSON, and turnkey global distribution provides low-latency access for frequently read documents. This combination of native JSON storage, automatic indexing, and direct querying exactly meets the requirement.
- ✗
Azure Table Storage
Why it's wrong here
Azure Table Storage is a key-value store where each entity requires a PartitionKey and RowKey, and queries for other properties cannot leverage secondary indexes. A JSON document would need to be serialized into a single value, preventing efficient querying by arbitrary JSON properties unless the entire table is scanned. Although it is inexpensive and fast for simple lookup patterns, it is not a JSON document database.
Go deeper
Related to this question
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Data Roles and Core Concepts
Key term
Azure Cosmos DB
Azure Cosmos DB is a fully managed, globally distributed NoSQL database service that offers fast reads and writes anywhere in the world with automatic scaling and multiple consistency models.
Key term
Data
Data is raw, unprocessed information, like numbers, words, or measurements, that can be stored, processed, and analyzed by computers.
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