Digital materials are the result of the mediation of information technology and data. That is, the digital object that is developed on a particular software and hardware platform can be viewed as it was originally conceived only on that particular platform. Viewing web sites illustrates this point. The software used to view them – the web browsers – are configurable by the user in relation to characteristics such as the font size and colour, unless the web site designer insists that the browser displays a site in a particular way. The experience of viewing that web site will be different for users who access that site using soft- ware and hardware that differs from that used to develop the site. Strictly speaking, observes Eastwood, ‘it is not possible to preserve an electronic record.
It is only possible to preserve the ability to reproduce an electronic record. It is always necessary to receive from storage the binary digits that make up the record and process them through some software for delivery or presentation’
(Eastwood, 2002, p.77, citing Thibodeau, 2000).
This mediation aspect – the rendering or presentation (and re-presentation) of the digital files – is an important point to appreciate for digital preservation.
Digital objects are not simply a bit-stream; rather, they are a combination of hardware, software and computer file. The bit-streams of computer files have to be processed technically before they make sense to a user:
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Digital materials, technology and data 77
Hardware Software Computer
file
Digital object
The computer file may look and behave differently from how it was origi- nally intended to look and behave, if the hardware and software combination differs. This difference may be so extreme that the authenticity of the digital object is called into question (Digital Preservation Testbed, 2003, pp.13–14).
(These concepts have been considerably extended in the consideration of digital objects as physical, logical or conceptual objects in Chapter 1.)
Some implications of this dependency of digital objects on software are listed in the UNESCO Guidelines. Three different kinds of software dependency are identified:
• digital objects that are simple and less dependent on specific software (plain text in ASCII files is an example)
• digital objects that depend on more complex software that is, however, generic (such as HTML)
• and digital objects that depend on software specific to a particular hard- ware platform or operating environment (such as spreadsheets and word processing software).
The example of web sites that incorporate search and retrieval functions indi- cates that some digital objects contain executable files and software programs, and others may contain combinations of all of the above. The extent to which the digital object is dependent on software has a significant effect on the way in which it can be preserved (UNESCO, 2003, p.124).
Furthermore, it is not possible to preserve originals of digital materials, because migration is probably inevitable at some stage in the preservation process, and migration involves technology. We are preserving copies of the originals, ‘preservation copies made according to the particular methods and strategies that are appropriate or expedient’ (Gilliland-Swetland, 2002, p.198).
Crucial to the development of digital preservation was the realization that separating the technology from the data was the key. The technology (hardware and software) was changing rapidly and would continue to do so. Earlier thinking placed a high emphasis on preserving the ability to read computer files in the software that was used to create them. Digital preservation solutions such as museums of technology and emulation were proposed. Once it was acknowl- edged that the digital file would have to be transferred from one medium to another and that it could be viewed using a hardware/software combination different from that with which it was created, the focus shifted from maintaining access to obsolete software and hardware to determining which characteristics or attributes of the digital file are essential to maintain access to in the future, and how this can be achieved on current and future hardware/software combi- nations. However, this change in thinking brought its own problems, as an early statement about electronic records recognized:
The content of a traditional record is recorded on a medium (storage device, like a piece of paper) and cannot be separated from this medium.
The content of an electronic record is also recorded on a medium, but from time to time it has to be separated from the original device and transferred to other, and often different types of, storage devices whenever it is retrieved or when necessitated by technological obsoles- cence. Unlike traditional records, an electronic record is therefore not
78 What Attributes of Digital Materials Do We Preserve?
permanently attached to a specific medium or storage device, so the opportunities for corruption grow. This presents additional problems in ensuring that the record’s authenticity and reliability are maintained (International Council on Archives. Committee on Electronic Records, 1997, p.22).
The history of the response to digital preservation of the archives community in Australia illustrates this changing awareness and focus. Early responses to the issues of preserving electronic records, dating from around 1990, stemmed from pre-digital preservation attitudes, and tended towards the requirement that the artifacts themselves be preserved and kept accessible. Consequently emphasis was placed on maintaining hardware and on the longevity of media types such as disks and tapes. By the mid-1990s the thinking had changed and it was accepted, according to National Archives of Australia staff in May and June 2004, that ‘the solution had something to do with software applications . . . the archives community generally hovered around this idea that somehow or other, if you could preserve the application, then you could preserve the data’. However, by the late 1990s the archives community recognized that the ‘problem is a data problem, it’s not a software application problem’. A new understanding of how software interacts with data was emerging:
At the end of the day records are just data and data are just records, and in that process we came more to a clearer understanding of how software applications interact with data to produce records . . . That radically changed the possibilities of finding solutions, and we found the solution very quickly . . . We really started to give serious attention to this in the year 2000 and we had our basic approach worked out within a year. The basic idea [was] of normalizing materials into XML structures and ensuring that those XML structures have appropriate metadata kept with them, so that . . . the provenance and all the other authenticity issues about them could be re-established (Interviews with National Archives of Australia staff, May-June 2004).
Once we have realized that the key is to ensure the preservation of the data, regardless of the hardware and software platforms that the data will be pro- cessed on, then we need to pay a lot more attention to that data – to the attrib- utes of the data to be preserved and the level of acceptable loss and alteration of the data.
As already noted, the process of preserving digital materials inevitably means that they are altered. While at one level digital preservation is a relatively simple matter of preserving the bit-stream, the result is meaningless unless the means to read and interpret that bit-stream are available, either by preserving them or developing software that makes them accessible. We might, for example, emulate a software application with a resulting loss of some functionality, affecting the ability of that software to fully interpret the data. What effect does this have on the authenticity of the digital object? Is some loss acceptable?
If we can determine what attributes of that digital object are essential for us to understand it, then we can seek to preserve these attributes. For example, the colours presented on the screen may not be significant for text content, but it could be significant for understanding a web page. ‘Document-like’ digital 1111
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materials, typically in PDF, HTML, XML, or SGML file formats, ‘embody data content, structure and presentation’ (Van der Werf, 2002) and can be read using software other than that in which they were created. (In fact, this is the very characteristic of these file formats that makes them so useful for digital preser- vation purposes.) Other digital materials, typically educational software, games, and web animations, are ‘executable’ files, that is, they are in a format that is directly read by a computer as a program and is run (‘executed’). These are usually in proprietary file formats, not re-usable in other contexts (Van der Werf, 2002). The determination of which attributes of digital objects are essential to maintain into the future has been addressed largely by the recordkeeping community in relation to establishing the requirements for authentic digital records (considered later in this chapter). Once these have been established,
‘combinations of data, software and hardware that will re-present those elements as accurately as required’ need to be maintained (UNESCO, 2003, pp.123–124).
An allied question is: What level of loss or alteration of data is accept- able? The UNESCO Guidelines suggest that decisions about this are likely to be required by digital preservation programs; as already noted, some ‘loss of content, loss of the original “look and feel”, or loss of some original functions’
is likely. Further thinking about this question will assist in determining what the essential attributes of digital objects are (UNESCO, 2003, p.123).