Raymond Blum with Betsy Beyer at ACM
First, let’s define digital permanence and the more basic concept of data integrity.
Data integrity is the maintenance of the accuracy and consistency of stored information. Accuracy means that the data is stored as the set of values that were intended. Consistency means that these stored values remain the same over time—they do not unintentionally waver or morph as time passes.
Digital permanence refers to the techniques used to anticipate and then meet the expected lifetime of data stored in digital media. Digital permanence not only considers data integrity, but also targets guarantees of relevance and accessibility: the ability to recall stored data and to recall it with predicted latency and at a rate acceptable to the applications that require that information.
To illustrate the aspects of relevance and accessibility, consider two counterexamples: journals that were safely stored redundantly on Zip drives or punch cards may as well not exist if the hardware required to read the media into a current computing system isn’t available. Nor is it very useful to have receipts and ledgers stored on a tape medium that will take eight days to read in when you need the information for an audit on Thursday.
The Multiple Facets of Digital Permanence
Human memory is the most subjective record imaginable. Common adages and clichés such as “He said, she said,” “IIRC (If I remember correctly),” and “You might recall” recognize the truth of memories—that they are based only on fragments of the one-time subjective perception of any objective state of affairs. What’s more, research indicates that people alter their memories over time. Over the years, as the need to provide a common ground for actions based on past transactions arises, so does the need for an objective record of fact—an independent “true” past. These records must be both immutable to a reasonable degree and durable. Media such as clay tablets, parchment, photographic prints, and microfiche became popular because they satisfied the “write once, read many” requirement of society’s record keepers.
Information storage in the digital age has evolved to fit the scale of access (frequent) and volume (high) by moving to storage media that record and deliver information in an almost intangible state. Such media have distinct advantages: electrical impulses and the polarity of magnetized ferric compounds can be moved around at great speed and density. These media, unfortunately, also score higher in another measure: fragility. Paper and clay can survive large amounts of neglect and punishment, but a stray electromagnetic discharge or microscopic rupture can render a digital library inaccessible or unrecognizable.
It stands to reason that storing permanent records in some immutable and indestructible medium would be ideal—something that, once altered to encode information, could never be altered again, either by an overwrite or destruction. Experience shows that such ideals are rarely realized; with enough force and will, the hardest stone can be broken and the most permanent markings defaced.
In considering and ensuring digital permanence, you want to guard against two different failures: the destruction of the storage medium, and a loss of the integrity or “truthfulness” of the records