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Introduction

Archaeologists are creating digital data in the course of their work, and their preservation is as significant to the future of the archaeological record as the preservation of conventional finds and paper archives. Modern excavations create huge amounts of digital information. Whether it is the on-site recording of the archaeology, specialist databases created during post-excavation or publication standard interpretative maps and plans, digital information has the potential to be created at every stage from assessment to publication.

Traditionally the entire archive would have been transferred to a museum at the end of a project's life, but in a recent survey into the state of museum archaeological archives in England, Swain (1999, 47) noted that "most museums do not have the correct technology to store, access and curate in the long-term those archives for which computer files form an important part." The Swain report also illustrated that little digital material was being transferred to museums for archival purposes. This comment is echoed in Strategies for Digital Data (Condron et al 1999, 29-32, and Figure 6.5), which showed that the majority of extensively digitised projects are either retained by their creators or are in the hands of local government organisations. Strategies for Digital Data, however, also highlighted the inadequate archival policies of these organisations (Condron et al 1999, 33-39). Archaeologists are in danger of losing digital material, much of which is central to the archaeological record.

The Digital Archiving Pilot Project for Excavation Records (DAPPER) arose from these concerns. DAPPER was a collaborative venture between the Archaeology Data Service (ADS), English Heritage (EH), the Museum of London Archaeology Service (MoLAS) and the Oxford Archaeological Unit. The Pilot Project aimed to:

• investigate how digital project information could be effectively archived
• research the delivery of excavation archives over the Internet
• work on costed models for archiving and delivery
• assess the user reaction to digital project archives
• provide examples of best practice in the emerging field of digital project archiving
• explore the relationship between digital archiving and publication

Choosing projects to archive

In order to demonstrate the concept and potential of this new form of information provision it was necessary to choose the excavations to archive with care. After a lengthy consultation period two reasonably large and 'high profile' sites were identified as most suitable: the Royal Opera House excavation by the Museum of London Archaeology Service and Eynsham Abbey, excavated by the Oxford Archaeological Unit.

Excavations at Eynsham Abbey
Between 1989 and 1992 the Oxford Archaeological Unit (OAU) undertook a full excavation of part of the precinct of the medieval abbey, revealing part of the cloister and south ranges, kitchens and domestic buildings. Evidence for earlier activity included the 11^th century Anglo-Saxon abbey and earlier Minster, and a Bronze Age enclosure.

Excavations at The Royal Opera House
Following exploratory work in 1995 full-scale excavations were undertaken in 1996 by MoLAS at the site of the Royal Opera House in Covent Garden, Greater London. The excavation examined the largest area of the Saxon trading port of Lundenwic so far to become available and has provided a wealth of information on the form and economy of this settlement.

Key factors in identifying appropriate projects

• Both of these projects were at their dissemination stages and had large, quite different, digital archives to deposit
• Both units were keen to participate in the project and there was a contact person in both who was involved in the excavation and creation of digital data. The willingness of the participants was a crucial factor in the success of the project. The digital archive is something of a new concept and it was important to enter into a collaborative working relationship with project partners
• Importantly, there was a community of scholars who would want access to the raw data from the excavations. This would enable the demonstration of the effective re-use of the digital archives
• The projects were undertaken by different units to avoid the results being skewed by one set of working practices

The contents of the archives

It is important to note that in neither case was the digital archive planned as part of the dissemination phase of the project and that both Eynsham Abbey and the Royal Opera House will be published as traditional monographs. The resultant digital archives are, however, remarkably similar in their content. This is due to their origin as the residues of large-scale, well-funded post excavation projects. Both archives are comprised of essentially the digital residues of the post-excavation process and represent a digital version of the 'research archive'.

Eynsham Abbey
The project was never designed as an exercise in digital data collection or management, but rapid changes in computer technology in the last five years has meant that the project developed in this direction.

The downloadable archive contains text files, databases made available as comma delimited text, JPEG images, a 3D reconstruction of the medieval abbey available in DWG or DXF format (i.e. AutoCAD) and numbers of digitised drawings also available as DWG or DXF files. Image files have also been deposited in both preservation and dissemination formats.

The contents of the Eynsham digital archive can be summarised as follows:

Royal Opera House
All data from the Royal Opera House project was collected in computer based formats. This excavation was the first for which MoLAS used its state-of-the-art integrated database and GIS recording system. The on-line archive is currently incomplete but contains Geographical Information System (GIS) files, interpretive groupings and data files consisting of context, artefact and ecofact attribute sets. The digital archive is currently in the process of completion and only those elements that will remain unaltered have been deposited. The remainder of the digital archive consisting of the higher-level interpretative datasets will be deposited when the publication is complete. A much wider variety of queries are possible with the full dataset permitting assemblages to be related directly to buildings and periods of activity.

Accessing the archives

Although DAPPER has led the way in developing digital archives, if they were difficult to find, or impossible to use, the project would ultimately be a failure. Consequently the project also concentrated on assessing the utility of the digital archives and gained feedback from the user community. This was done in order to consider the archives at an early stage and modify them prior to the public launch.

Resource discovery
The Eynsham Abbey and Royal Opera House excavation archives have the potential to be accessed in one of three ways:

Using the ArchSearch catalogue. The site level metadata records can be searched, for example a Keyword search for 'Eynsham' and 'Abbey' results in 51 records being returned. One of these records has 'Excavation Archive' included in the Name of Resource field. This record leads to a more detailed catalogue record detailing the site, its excavators and its digital archive, which may be accessed via a hotlink entitled 'Resource Details' (Figure 1). Equally if a user was interested in GIS resources they could do a What Search for 'GIS'. This would return five records, one of which included 'Excavation Archive' in its title to indicate that GIS resources were available from the Royal Opera House archive.	Figure 1: A section of the metadata record for the Royal Opera House excavation
In the left hand frame of ArchSearch there is a Project Archive button (Figure 2), which leads the user to a list of projects with downloadable resources.	Figure 2: The Project Archive button
Although not yet implemented by the OAU or MoLAS, it is possible for both units to hot-link directly from their own web pages to their project archives.

Resource delivery
One of the major data delivery issues concerned the user interface and revolved around the issue of whether a complex, visually pleasing, heavily packaged interface should be developed, or whether the raw data should be simply presented? The heavily packaged interface would be user friendly and consequently may increase access to the data. This approach, however, was rejected as it would have been prohibitively expensive to produce, would have set a precedent for all subsequent deposits and the heavily packaged nature of the data would probably present migration problems. More importantly perhaps, the packaging of data may restrict its potential for reinterpretation. Consequently it was decided to present the data in standard formats with sufficient on-line support documentation to enable the re-use of the data. This was regarded as the ideal, sustainable cost-effective solution.

The resource delivery issues brought the idea of who the data is aimed at into focus. The ADS receives its core funding from the Higher Education sector and consequently it is the scholarly community at which its data resources are aimed. Equally the ADS user community, as reflected in Strategies for Digital Data (Condron et al 1999), clearly wanted raw, rather than packaged data. The simple, unpackaged DAPPER interface consequently reflects the professional archaeological community's desire for raw data.

The ADS have recently submitted a proposal to the Joint Information Systems Committee to fund the creation of an online tutorial into the reuse of the digital resources from the DAPPER excavation archives. This will involve the re-purposing of the raw data into Internet deliverable teaching modules and will expose the next generation of archaeological students to the manipulation and re-use of digital excavation archives.

The cost of digital archiving

Digital archiving entails expenditure, both in the setting up and running of a digital archive and in preparing, depositing, accessioning and curating the information resources. If archiving of the digital component of fieldwork is to become a part of the everyday practice of archaeology, DAPPER also had to demonstrate the commercial case for such archives. The pilot has allowed us to quantify the effort and costs to both units and archives in the preservation and dissemination of computer-based data.

In a recent survey into the use and re-use of digital information in archaeology (Condron et al 1999, 70-71), the respondents clearly accepted the principal of cost recovery for digital archives, although the notion of charging re-users for access to information was firmly rejected. Given this clear steer from its user community the ADS has formulated and implemented a charging policy.

The central tenets of this policy are that:

• the use of ADS resources will be supported free of charge
• archiving costs should be recovered from the body funding the archaeological investigation, or research, wherever possible

The experiences gained from DAPPER have proved invaluable in the development of the ADS charging policy (ADS 1999a). More information on the charging policy, including a detailed breakdown of the costs and charging categories is available online http://ads.ahds.ac.uk/project/userinfo/charging.html

The Eynsham Abbey and Royal Opera House digital archives are both essentially research archives. Yet they differ quite markedly in their cost. This is clearly due to the ways in which both sites were analysed during post-excavation. Although the stratigraphic drawings of both sites are available digitally, the use of GIS by MoLAS ensured a deposit of 3 files, as opposed to the 404 Eynsham Abbey site plan CAD files. The 80 structure plans, 15 phase plans, 2 sections, a trench plan, a composite plan and a 3-D reconstruction of the Abbey also swelled the number of Eynsham Abbey CAD files. Consequently the cost of archiving is closely related to the presentation of the drawing information. It should not be assumed, however, that GIS is preferable to CAD because it is more cost effective to archive. Both file formats have their own distinct advantages and disadvantages. The GIS structure of the Royal Opera House archive, for example would require specialist software and training to facilitate effective understanding and reuse of the data. It is consequently difficult for a user with little knowledge of GIS to use the archive. On the other hand the Eynsham Abbey archive is structured like a traditional archaeological publication, with its separate structure and phase plans. With appropriate viewers, the CAD files can be accessed via the Internet. Consequently the CAD presentation of the data can open up access to the information for non-expert users. Yet for highly experienced users the MoLAS GIS offers a very powerful analytical tool, with interpretative functionality that is beyond CAD. It is recommended that units continue to undertake their post excavation in the ways most appropriate to them and that the production of a comprehensive digital archive should come before matters of cost.

In its Charging Policy the ADS state that "it is usual for digital archiving costs to add an overhead of less than 5% to the total project budget" (ADS 1999a). DAPPER has illustrated that for projects of the scale of Eynsham Abbey and the Royal Opera House, the actual cost of digital archiving can be as little as 1% of the total project budget. It must be recognised, however, that this 1% figure relates only to large-scale excavation projects. For medium to smaller-scale projects with a variety of files, the actual cost of archiving will be represent a greater proportion of the total budget and be in the region of 3-5% of the total project budget.

Contributing to the debates on digital project archiving

The Eynsham Abbey and Royal Opera House excavations were both extensive and well funded post-excavation projects that produced research level archives. It is recognised, however, that not every archaeological project merits this level of expenditure and archiving. Consequently DAPPER enabled the ADS to consider the different levels of digital archiving. Four distinct types of digital archive can be produced (Figure 3). These archives are:

• Index level archive
  The index level archive should be regarded as the minimum digital archive. Where the results of the project do not warrant further assessment work an index level archive should be preserved. This should contain an index record for the ADS catalogue and a site summary document.

• Assessment level archive
  The assessment allows the potential for the project data to be ascertained accurately and results in the creation of a larger digital archive. Where further research into the site is not warranted the assessment level archive should be preserved. This should contain an index record, the project design, the assessment report, any specialist assessment level databases and a site matrix.

• Research level archive
  Where the project is archaeologically and academically significant further analysis beyond the assessment will be undertaken. This results in the creation of a large and complex digital archive. The analysis will result in the production of a research level digital archive and the traditional publication of the site. Here the digital archive will not be integrated into the final project report and effectively represents the residue of the analytical and publication process. The archive should contain an index record, the project design, the research archive including stratigraphic databases, digital plans, site matrix, artefactual and ecofactual databases, the site, artefactual and ecofactual reports.

• Integrated Archive
  The scholarship involved in the creation of traditional archaeological monographs results in the creation of large amounts of digital data. This data may simply be incorporated into the Research Level archive. Yet this misses an opportunity to create an integrated archive in which the data is articulated with the text of the report. It is envisaged that an integrated archive would link seamlessly between the text of the report and the fully digital site archive. Ideally users would be able to query the entire spectrum of site data through a range of interfaces, including searchable relational databases and web-based GIS. The integrated digital archive provides the opportunity to take unwieldy technical data out of the excavation report and locate it in a universally accessible environment. Modern archaeological datasets often do not translate well into the written reports, especially if much of the information is in the form of CAD drawings, GIS or relational databases, which loose their utility when removed from their digital format. Consequently the digital archive offers the opportunity to place data in a facility that actively encourages its reuse and reinterpretation. If project data were located in a digital archive this would have profound implications for the ways in which archaeological research is published. If the correct linkages can be developed between the traditional paper or Internet publication and the digital archive this would enable the final project report to be slimmer and more synthetic and less bogged down in detailed description. The beginnings of this form of dissemination strategy are to be found in some of the papers in Internet Archaeology (http://intarch.ac.uk).

Figure 3: A model for the production of archaeological digital archives

Conclusion

DAPPER has delivered:

• the archiving and Internet delivery of digital project data
• costed models for digital project archiving
• user reactions to the archives
• contributions to the debates on digital project archiving

The archiving and Internet delivery of digital project data
DAPPER enabled the Archaeology Data Service to develop and implement the world's first online digital project archive.
DAPPER has provided some 'start-up' funding to help with the development of the Project Archives section of ArchSearch. It provided the necessary digital infrastructure that subsequent deposits will benefit from; for example, the creation of the Download support pages is a vital component of the digital archive.
DAPPER gave the University-based service a valuable introduction to commercial archaeology and has enabled it to develop its Charging Policy (ADS 1999a)
DAPPER also enabled the ADS and the units the chance to discuss some of the inevitable queries that the units had concerning digital archives and enabled the ADS to reassess its policies and procedures in the light of unit concerns.
DAPPER provided the necessary funding and time for the Museum of London Archaeological Service and the Oxford Archaeological Unit to prepare their data for deposit and to reassess and develop their post-excavation procedures and documentation.

The costs of digital archives
DAPPER has demonstrated that an effective digital archive can be delivered for a fraction of the total project cost. For substantial fieldwork projects the DAPPER project suggests that the estimated archive deposition cost (approximately 5% of the total project budget) as reported in the ADS Charging Policy (ADS 1999a) can be modified downwards, to less than 1% of the total project budget. These costs need to be written into the original budgetary specifications.

Evaluating user reactions
The results so far from DAPPER have been very encouraging. The Royal Opera House archive was released in August, followed by Eynsham Abbey in October 1999. Following the launch of the excavation archives the ADS website has received an increased number of visitors and has experienced record-breaking user figures. Indeed over 8,000 people have visited the project archives and either accessed or downloaded approximately 10,000 separate files within the archives. People are downloading and starting to reuse the data, indeed one researcher remarked that the archives would prove very useful in his research and that the time and money he expended on downloading the entire Royal Opera House archive and reassembling it into its GIS form was well worth it.

The DAPPER resources are also being used as teaching datasets in the Archaeological Information Systems Masters degree that is being run at the University of York. Other universities, such as Durham and Glasgow, have also expressed an interest in using the DAPPER resources.

DAPPER has been a highly successful pilot project. It represents a new beginning both for the archiving and dissemination of digital archaeological information.

Return to index of papers for April, 2000, SAA Session "Digital Data: Preservation and Re-Use"

About this document:

• Title: "Digital Archiving Pilot Project for Excavation Records (DAPPER)," a paper for the April, 2000, SAA Session "Digital Data: Preservation and Re-Use"
• File name: dapper.html
• Author: Dr. Damian Robinson, Archaeology Data Service
• Revision history: First posted 7 March 2000. There are no anticipated revisions to this document.
• Internet access: This document is maintained at csaws.brynmawr.edu by the Center for the Study of Architecture and Harrison Eiteljorg, II. Note that there may be changes in computer addresses that are beyond the control of CSA.
• Long-term availability: This document will be maintained for electronic access for the foreseeable future; it will not be archived.
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