Which of the following is a characteristic of both a database and a flat file?

Concurrent users are typically supported by database management systems with concurrency control mechanisms, which flat files generally lack.

Persistence refers to the ability of data to outlive the process that created it; both flat files and databases store data on non-volatile storage, making it persistent.

While simple queries can be performed on flat files (e.g., searching text), complex querying capabilities with indexing and relational joins are characteristics of databases, not flat files.

Data definition (schema) is a structured characteristic of databases, often enforced through a DBMS, whereas flat files have a less formal or unenforced structure.