Is access to data obtained within a transaction prohibited, and are such operations allowed during another transaction?

Access to data obtained within a single transaction is usually isolated from other transactions according to the transaction isolation level in the DBMS. This means that changes made in one transaction are not visible to other transactions until it is committed.

If a transaction is not completed (not committed), other transactions cannot access this data — this prevents "dirty reads." After a commit, the data becomes visible to other transactions.

Thus, prohibiting access to data within one transaction for other transactions is normal behavior, ensuring data integrity and consistency. Read and write operations are allowed within a single transaction, but other transactions will see these changes only after the commit.