Category: Digital Preservation

Preservation Description Information

Also known as:

Simply put

Preservation Description Information (PDI) is the supporting information that a digital archive keeps alongside the actual content it is preserving, so that the content can continue to be preserved and understood over time. Rather than being the item itself, PDI describes and documents the item in ways that help keep it authentic, traceable, and usable in the future. It is one of the two main types of information held within a preservation information package.

Formal definition

Within the OAIS reference model, Preservation Description Information (PDI) is defined as the information necessary for the adequate preservation of the associated Content Information. It is one of two components of an Information Package, the other being the Content Information itself, and it is typically categorized into distinct classes of preservation-supporting information. PDI is conceptually distinct from the Content Information it accompanies: it does not constitute the preserved object but provides the contextual and documentary information required to sustain that object's ongoing preservability. Note that the precise categories and subdivisions of PDI, and the manner of their implementation, depend on the specific version of the OAIS framework and on the practices of the preserving repository.

Why it matters

Preservation Description Information matters because preserving a digital object is not simply a matter of storing its bits. Over time, the ability to demonstrate that a preserved item is authentic, to trace where it came from and what has happened to it, and to keep it usable and understandable can erode if the surrounding documentation is not deliberately maintained. PDI addresses this need by holding the supporting information that allows a repository to continue preserving and interpreting Content Information rather than the content alone. Within the OAIS reference model, it is precisely this preservation-supporting information that distinguishes a managed digital archive from mere storage.

The stakes are clearest when the qualities that make something a trustworthy record are considered. Digital preservation programs commonly aim to sustain the ongoing usability of records while retaining qualities such as authenticity over long periods. Without adequately captured PDI, a repository may retain the object itself yet lose the ability to show that it is what it purports to be, or to explain the context needed to render and understand it. Because PDI is conceptually separate from the Content Information it accompanies, treating the two as a single undifferentiated blob risks overlooking the documentation on which long-term preservability depends.

The practical significance of PDI also lies in its role as the second essential component of a preservation Information Package. Repositories that overlook this component may find that content survives technically but cannot be defended as reliable evidence in the future. It should be noted that the specific categories of PDI and how they are implemented depend on the version of the OAIS framework in use and on the practices of the individual repository, so organizations should scope their PDI requirements to their own preservation goals rather than assuming a universal standard.

Who it's relevant to

Digital preservation specialists

Those responsible for maintaining digital objects over the long term rely on PDI to sustain the continued preservability of Content Information. Because PDI must include whatever is necessary to adequately preserve the particular content it accompanies, these specialists are typically the ones who determine what supporting information to capture and how to categorize it, working within the OAIS framework version and repository practices that apply to their environment.

Archivists and repository managers

Archivists concerned with sustaining the authenticity and usability of records benefit from understanding PDI as the second essential component of an Information Package alongside Content Information. This distinction helps them ensure that documentation supporting authenticity, traceability, and future understanding is preserved deliberately rather than assumed to be inherent in the content itself.

Records managers overseeing long-term retention

For records identified for long-term or permanent preservation, records managers need to appreciate that keeping the object is not sufficient on its own. PDI provides the contextual and documentary information that helps keep a preserved item authentic, traceable, and usable over time, which supports the broader goal of retaining records as reliable evidence of activity.

Systems and repository designers

Those designing or configuring preservation systems should account for PDI as a distinct type of information within the Information Package. Because the categories and implementation of PDI depend on the OAIS framework version and repository practices, designers should scope their implementation to their organization's preservation goals rather than assuming a fixed structure.

Inside PDI

Provenance Information

Documents the origin, custody history, and chain of responsibility for the content, including who created it and how it has been handled or altered over time. This supports assessments of authenticity by establishing a defensible record of the content's lineage.

Context Information

Describes how the content relates to its surrounding environment, such as the reason for its creation, its relationship to other content, and the systems or activities that produced it. This helps establish the meaning and usability of the content over the long term.

Reference Information

Provides the identifiers and descriptors used to locate and unambiguously refer to the content, such as persistent identifiers or catalogue entries. This supports retrieval and citation across time.

Fixity Information

Provides mechanisms, such as checksums or other integrity indicators, that allow verification that the content has not been altered in an undocumented way. This supports assessments of integrity, though it typically demonstrates unaltered state rather than proving broader reliability on its own.

Access Rights Information (in some framings)

Where included, describes the rights, restrictions, and conditions governing use of the content. Whether this element is treated as part of PDI or handled separately can vary depending on the framework or implementation, so practitioners should confirm the scope in their own context.

Common questions

Answers to the questions practitioners most commonly ask about PDI.

Is Preservation Description Information the same as the content being preserved?

No. PDI is a category of metadata associated with the content, not the content itself. In the OAIS reference model, PDI is the information that supports the long-term preservation of a Content Information object, describing aspects such as its provenance, context, reference, fixity, and access rights. The digital object or data being preserved is distinct from the PDI that surrounds and supports it. Confusing the two can lead to preserving content without the descriptive and evidential information needed to keep it authentic and usable over time.

Does PDI serve the same purpose as ordinary descriptive metadata used for discovery?

Not exactly. Descriptive metadata is often oriented toward resource discovery and retrieval, whereas PDI is specifically concerned with sustaining a preserved object's authenticity, integrity, and interpretability over the long term. PDI typically encompasses information about origin and custody, contextual relationships, identifiers, integrity or fixity checks, and rights. While there can be overlap with discovery metadata, PDI's function is preservation support rather than cataloguing or search, and treating them as interchangeable may leave preservation requirements unmet.

How should an organization decide what information to capture as PDI when ingesting content?

In practice, the information captured is usually guided by the OAIS framework's categories, which typically include provenance, context, reference, fixity, and access rights. Organizations often map their own metadata sources to these categories during ingest, drawing on system logs, custodial records, identifiers, and integrity checks. The appropriate level of detail generally depends on organizational policy, the value and risk profile of the content, and any applicable retention or preservation obligations, which vary by jurisdiction and sector.

Where does PDI typically fit within an ingest and storage workflow?

PDI is generally assembled and associated with the Content Information as part of forming an Information Package, often during ingest processing. Depending on the repository's design, PDI may be stored alongside the content, in a linked metadata store, or in a combination of both. The key implementation concern is usually maintaining a reliable and durable association between the content and its PDI throughout storage and any subsequent transformations, so that the two are not separated in ways that undermine authenticity.

How can the integrity of PDI itself be maintained over time?

Because PDI supports the trustworthiness of preserved content, many repositories apply integrity controls to the PDI as well, such as fixity checks and controlled update procedures. Changes to PDI, particularly to provenance information, are often recorded so that the history of the object and its metadata remains auditable. The specific controls used typically depend on organizational policy, the preservation system in use, and the assurance level the organization seeks to demonstrate.

What implementation challenges commonly arise when maintaining PDI across preservation actions such as format migration?

Preservation actions like format migration or normalization can alter the content and therefore need to be reflected in the PDI, particularly within provenance information. A common challenge is ensuring that each action is documented so that the chain of custody and processing history remains complete and defensible. Organizations often address this by updating provenance records at each step and by preserving information about prior representations, though the exact approach depends on the repository's capabilities and the organization's preservation policy.

Common misconceptions

PDI is the same as the content or digital object it accompanies.

PDI is the information needed to preserve, understand, and validate the content over time, not the content itself. It sits alongside the content object as supporting information; the distinction between the object and its preservation metadata is deliberate and should be maintained.

Fixity Information alone establishes that a record is authentic and reliable.

Fixity typically supports integrity by helping verify that content has not been altered in an undocumented way. Authenticity and reliability generally depend on the combination of provenance, context, and reference information as well, so no single PDI element should be treated as sufficient on its own.

Capturing PDI is a one-time task completed at ingest.

PDI often needs to be maintained and updated across the preservation lifecycle, for example as custody changes, fixity is re-verified, or context evolves. Treating it as static risks undermining the very authenticity and usability it is meant to protect.

Best practices

Capture provenance, context, reference, and fixity information at the point of ingest wherever feasible, since reconstructing these elements later is often difficult or unreliable.

Keep PDI logically associated with, but distinct from, the content object it supports, so that the record and its preservation metadata can each be managed and verified appropriately.

Re-verify fixity information on a scheduled and defined basis to detect undocumented alteration, and document the outcome of each verification as part of the ongoing preservation record.

Update provenance and custody information whenever responsibility for the content changes, so that the chain of custody remains defensible over the full preservation period.

Confirm, within your own framework and implementation, whether access rights information is treated as part of PDI or handled separately, and document that scoping decision to avoid ambiguity.

Align PDI practices with organizational preservation policy and any applicable jurisdictional or sectoral requirements, recognizing that specific obligations depend on jurisdiction, sector, and institutional context.