Editing Data integrity (section)

== Integrity types ==

=== Physical integrity ===
Physical integrity deals with challenges which are associated with correctly storing and fetching the data itself. Challenges with physical integrity may include [[electromechanics|electromechanical]] faults, design flaws, material [[fatigue (material)|fatigue]], [[corrosion]], [[Power outage|power outages]], natural disasters, and other special environmental hazards such as [[ionizing radiation]], extreme temperatures, pressures and [[g-force]]s. Ensuring physical integrity includes methods such as [[Redundancy (engineering)|redundant]] hardware, an [[uninterruptible power supply]], certain types of [[RAID]] arrays, [[radiation hardened]] chips, [[ECC memory|error-correcting memory]], use of a [[clustered file system]], using file systems that employ block level [[checksum]]s such as [[ZFS]], storage arrays that compute parity calculations such as [[exclusive or]] or use a [[cryptographic hash function]] and even having a [[watchdog timer]] on critical subsystems.

Physical integrity often makes extensive use of error detecting algorithms known as [[error-correcting codes]]. Human-induced data integrity errors are often detected through the use of simpler checks and algorithms, such as the [[Damm algorithm]] or [[Luhn algorithm]]. These are used to maintain data integrity after manual transcription from one computer system to another by a human intermediary (e.g. credit card or bank routing numbers). Computer-induced transcription errors can be detected through [[hash functions]].

In production systems, these techniques are used together to ensure various degrees of data integrity. For example, a computer [[file system]] may be configured on a fault-tolerant RAID array, but might not provide block-level checksums to detect and prevent [[silent data corruption]]. As another example, a database management system might be compliant with the [[ACID]] properties, but the RAID controller or hard disk drive's internal write cache might not be.

=== Logical integrity ===
{{See also|Mutex|Copy-on-write}}

This type of integrity is concerned with the [[correctness (computer science)|correctness]] or [[rationality]] of a piece of data, given a particular context. This includes topics such as [[referential integrity]] and [[entity integrity]] in a [[relational database]] or correctly ignoring impossible sensor data in robotic systems. These concerns involve ensuring that the data "makes sense" given its environment. Challenges include [[software bugs]], design flaws, and human errors. Common methods of ensuring logical integrity include things such as [[check constraint]]s, [[foreign key constraint]]s, program [[assertion (computing)|assertion]]s, and other run-time sanity checks.

Physical and logical integrity often share many challenges such as human errors and design flaws, and both must appropriately deal with concurrent requests to record and retrieve data, the latter of which is entirely a subject on its own.

If a data sector only has a logical error, it can be reused by overwriting it with new data. In case of a physical error, the affected data sector is permanently unusable.