Database consistency is the alignment of all data points within a database system to preconditioned values, ensuring proper reading and acceptance of data. Establishing rules for transactions helps maintain this consistency. Inconsistent data can lead to errors in the dataset. Consistency also requires changes to any object across all tables where it is present. Database consistency does not guarantee correctness of data but ensures that entered data meets prerequisites. Weak and strong consistency levels dictate how many replicas or nodes must respond with new permissible data before acknowledging a valid transaction. Isolation levels are part of ACID properties, which compartmentalize certain pieces of data to prevent modifications by other user transactions.