See About Autonomous Transaction Processing in Using Oracle Autonomous Transaction Processing on Shared Exadata Infrastructure for a full description of the Autonomous Transaction Processing service. Autonomous JSON Database provides all of the same features, with this important limitation: you can store only up to 20 GB of data other than JSON document collections. There is no storage limit for JSON collections.
Development of NoSQL-style, document-centric applications is particularly flexible because the applications use schemaless data. This lets you quickly react to changing application requirements. There's no need to normalize the data into relational tables, and no impediment to changing data structure or organization at any time, in any way. A JSON document has internal structure, but no relation is imposed on separate JSON documents.
With Autonomous JSON Database your JSON document-centric applications typically use Simple Oracle Document Access (SODA), which is a set of NoSQL-style APIs for various application-development languages and for the representational state transfer (REST) architectural style. You can use any SODA API to access any SODA collection.
SODA document collections are backed by ordinary database tables and views. To use other kinds of data, subject to the 20 GB limit, you typically need some knowledge of Structured Query Language (SQL) and how that data is stored in the database.
With Autonomous JSON Database, a SODA collection can only contain JSON data. For example, you cannot have a collection of image documents or a collection that contains both JSON documents and image documents. This is a limitation relative to Autonomous Transaction Processing, where you can define such heterogeneous collections.
No matter what kind of data your applications use, whether JSON or something else, you can take advantage of all Oracle Database features. This is true regardless of the kind of Oracle Autonomous Database you use.
JSON data is stored natively in the database. In a SODA collection on an Autonomous Database it is stored in Oracle's native binary format, OSON.