Research Issues in Migration and Long-Term Preservation
Electronic Records Meeting
May 29, 1997
Long-term preservation and migration are concerns not only of the recordkeeping community, but also of other professions and institutions with stewardship or custodial responsibilities for information assets. Unanswered problems with preservation and access to information over time, including records in the archival sense, is acknowledged as a limitation to the development of digital libraries, electronic archives, electronic patient records, legal documentation, scientific databases, and administrative support systems. Properly framed research questions could draw support from a variety of sources to address the conceptual, process, and technical aspects of long-term preservation using multi-disciplinary methods and expertise.
In 1996, a task force commissioned by the Commission on Preservation and Access and the Research Libraries Group issued a report on preserving digital information.
The underlying assumptions behind the research questions posed below are that exact replication of digital objects is rarely feasible or cost-effective and that archivists must accept some loss of information when migrating digital information from one generation of technology to the next. These assumption raises a series of questions about the characteristics of information loss and the specific conditions under which various types of information loss are acceptable.
Systematic research should be conducted to define acceptable levels of information loss during migration and to identify a set of minimal record attributes, which if not retained, would make investments in preservation pointless. These requirements will vary by format and by the circumstances of creation and use of the digital objects. Although current discussions of migration strategies acknowledge the wide variety of formats of digital objects, most migration strategies still address text or bit-mapped images, and there are no proven methods for migrating many formats of digital information. One research strategy is to define a taxonomy of document types which share common attributes in terms of their logical representations and hence are amenable to common migration strategies. At a very crude level, for example, data, text, images (still and moving), sound, maps, relations, hyperlinks, and executables all present format-specific challenges to migration. Migration will involve varying degrees of degradation, some of which may be readily acceptable, while others may destroy the meaning of the document.
Systematic research on migration should also examine the physical attributes of digital objects. Migration of digital objects with color encoding, compression, and encryption are examples of extremely complicated processes that require complex algorithms, software routines, and in some cases, specific hardware. We have little concrete research that can guide decisions about the possible loss of meaning and integrity of a digital objects if their physical structure is altered during the migration process. Some of the specific questions that this raises include:
It is important to recognize that there are a series of options for migration which have different implications for information loss, loss of functionality, and costs. The draft section on Migration Strategies distributed for this conference identified eight possible approaches to migration of digital information:
A related question concerns the degree of functionality that is needed or desirable when preserving digital information. Most of the computer science research on migration addresses the migration of legacy systems with as much functionality as possible from obsolete to new systems. Brodie and Stonebraker, propose a model of decomposition to simplify migration processes and to focus decision makers on the essential functionality that needs to be migrated.
The recordkeeping community has not defined which functionality is necessary to retain and which should be disabled in an archival system. There is a consensus that it is desirable, if not essential, to retain the functionality of retrieval and display. The concept of manipulability, however, is more problematic. It goes without saying that the holdings of an electronic archive should not be manipulable by its users. But there are many circumstances when the archives should be able to deliver to its users copies of documents which they can redact, reprocess, combine, and manipulate in a variety of ways. What remain ill defined is any clear set of criteria for manipulability linked to the original purpose of the record, its physical and logical format, or its potential uses.
Another area of research would address the requirements for retaining the relationships among digital objects. Strategies that only address migrations and transformations of discrete and bounded objects will not fully satisfy archival requirements because the relationships among archival documents is an essential element of preservation. This raises a series of questions about how to retain hyperlinks between and within documents, relations with relational data structures, and links between digital objects and executables. Addressing the technical aspects of these questions will require expertise in computer science and systems engineering. The archival community, nevertheless, has a responsibility to determine when it is necessary to retain the dynamic nature of electronic records and for proposing alternative strategies when relational structures cannot be migrated across incompatible system architectures.
Retaining the integrity and archival qualities of digital records will depend as much on how well the migration process is documented as on the specific migration strategies that are chosen. Robust protocols for documenting migration are needed so that subsequent users of the records can determine specifically which characteristics of the document were lost in each transformation, why a specific migration strategy was chosen, and under whose authority it was carried out. Documenting information loss during migration also offers an alternative to preserving an exact replica of a document and all of its associated functionality. For example, an alternative to retaining a set of external hyperlinks and all of the associated documents might be to generate a list of hyperlinked documents without the functionality of linking to the documents. If archivists can develop documentation standards for migration processes, then future users will have a basis for assessing how the document they are viewing at one point in time deviates from its first and subsequent instantiations.
These recommendations are all aimed toward a larger goal of developing records that are "self-migrating" and that are stored in systems which can be managed by artificial agents or other advanced tools. Most of the migration that has been carried out to date has required intensive human intervention to analyze the structure of records, assess the quality of associated documentation, and to develop customized routines for reformatting. Such processes are too costly and too labor intensive to scale up to a level that can address the volume and complexity of contemporary electronic records. An alternative strategy is to encourage computer scientists and software engineers to design "archiving agents" or "migration agents" that can detect records in endangered formats, select the appropriate migration strategy, make the necessary transformations, and document the changes. Not being an expert in computer science or systems engineering, I am uncertain of the feasibility of this proposal. Nevertheless, until the archival community specifies what such agents should do, we will not be able to explore this approach.
We also need research and development of cost models for the various approaches to migration. Decision making and preservation planning are compromised by the absence of cost data that addresses multiple formats and multiple options for migration. Such research should relate the losses of information and functionality to the costs of different migration strategies. Data on the costs incurred with various migration strategies would support a variety of policy and administrative decisions including appraisal and selection, choice of migration strategies, and the organization of the archiving function.
In this discussion, I have assiduously avoided drawing a sharp distinction between long-term maintenance of electronic records and preservation of other types of digital information. Both Bearman and Cunningham in their reviews of the digital archiving task force report stressed the need to differentiate records from other types of digital information.
In this discussion, I have concentrated on a series of requirements, specifications, options, and possible tools for migration. This is only a small subset of the research issues that are pertinent to long-term maintenance of electronic records. This research agenda is motivated, however, by a strong sense that the archival community has oriented its approaches to migration toward the problems and techniques of the generation of technology we are migrating from rather than taking advantage of the possibilities of the generation of technologies we are migrating to. An effective research agenda should explore how archivists can use emerging technologies to resolve the preservation problems caused by pervious generations of technology.