Created Date:30 October 1996
Last Updated:22 September 2020
Review Due:July 2021 (unless significant change)
Authors:Julian Richards, Catherine Hardman, Katie Green
Maintained By:Collections Development Manager

1. Introduction

The ADS Collections Policy has evolved over the past twenty-four years. It is written in four sections: Collections Development, Collections Management, Preservation, and Access and Use. Each of these sections defines a framework for activities within a broad area.

  • Collections Development focuses on the scope and nature of the content that will be collected by the ADS.
  • Collections Management provides a framework for the administration, description and storage of digital datasets.
  • Preservation defines long-term strategies for the archiving of collections.
  • Access and Use specifies where and how the ADS collections may be used, and identifies primary users.

The digital resources that the ADS preserves often represent primary research data. In cases where the data were 'born digital' or where the digital records now represent the only record of the research they are a precious and irreplaceable resource. Archaeologists and historic environment professionals have a professional duty to ensure the long-term preservation of these data which is enshrined in professional standards and national policies.

2. Collections Development

This section outlines the nature and scope of the ADS collections and collaborative activities.

2.1. Scope of Collections

The Collections Policy has developed throughout the life of the service in response to the needs and aspirations of its user community. The ADS Collections Policy can be thought of as embracing two central strands:

  • The delivery of high quality digital resources to the ADS user community.
  • The provision of a secure long-term archive for historic environment datasets.

In this way the ADS intends to maintain its position as a primary resource for any scholarly search for historic environment information and to break down traditional working practices by making primary historic environment data more widely available and accessible to the user community.

2.1.1. Geographical Range

The geographical remit of the ADS is to provide digital archiving facilities for all areas of the world in which UK historic environment researchers have research interests. Nevertheless it is recognised that since the ADS is UK-based and given that there is extensive high quality digital data for the historic environment of the UK that is in demand from UK-based archaeologists, and historic environmental professionals then the ADS should give priority to digital data of the historic environment of the UK. It is equally recognised that there is a substantial body of quality digital resources that are created by UK-based archaeologists working overseas. In some cases digital archives exist covering other countries and regions and the ADS works with such bodies to define areas of responsibility and data exchange.

2.1.2. Chronological Range

There are no chronological limits to the ADS collections, which covers the historic environment of the Palaeolithic to the present day. In the areas of evolution and archaeology of the early hominids, the ADS shall liaise with other digital archives to define areas of responsibility.

2.1.3. Thematic Range

The ADS collects datasets within the area broadly defined as Archaeology and the Historic Environment, including the material culture aspects of Ancient History and Classics. The ADS does not limit its collections policy according to any particular theme. Consultation with the user community indicates a broad range of research and teaching interests across all aspects of cultural history. Nonetheless, where the opportunity arises, the ADS seeks to build upon existing strengths to provide a critical mass of resources pertinent to specific themes.

2.1.4. A Layered Collections Policy

The ADS maintains a layered collections policy, providing access to datasets held by the ADS, resources maintained by a Co-operating Agency and links to authoritative Internet resources. The ADS Collection Policy may be broken into these four layers:

  • Archived
  • The resource is archived by the ADS and the ADS intends to preserve and keep the intellectual content of the resource available on a long-term basis. Such resources tend to be 'static', that is, the dataset is a coherent collection of digital information that is in its final state, and will not be changed.
  • Served
  • The resource is accessioned, catalogued and disseminated by the ADS, but another institution has primary responsibility for the content, maintenance and long-term preservation of the resource.
  • Brokered
  • The resource is physically hosted elsewhere and maintained by another institution but the ADS has negotiated access to it with a collaborating agency and includes metadata and links to it in its catalogues.
  • Catalogued
  • Electronic finding aids and metadata are held in the ADS catalogues facilitating high quality resource discovery. This may include pointers to resources delivered by another institution but for which ADS has assumed responsibility for the preservation of an offline digital archive copy.

Both Served and Brokered digital resources may be thought of as being ‘volatile’. Here the data creator is actively editing such a dataset. Where possible ADS policy will be to create metadata catalogue entries and to point to the online collections maintained by a Co-operating Agency (a brokered resource). In cases where the data creator wishes to make a volatile dataset available for re-use but lacks network access then the ADS may take a "snapshot" which is periodically refreshed (a served resource).

2.1.5. Collection Priorities

The ADS Collection Policy was originally developed through an extensive consultation process with its user community, published as Strategies for Digital Data. It continues to coordinate its collection priorities in conjunction with cognate organisations so as to ensure the preservation of orphaned quality digital datasets. These are recorded in the ADS Strategic Plan. It is anticipated that the collection priorities of the ADS will continue to develop in response to the emergence of a national digital archive policy within the UK. In the interim a number of guidelines can be proposed.

As part of its survey into the state of digital archiving practice in the UK and Ireland Strategies for Digital Data recommended that the appropriate standards and facilities for digital archives need to be documented. Strategies also recommended that a list of designated accredited digital archives are published. The Bedern Group are working towards this aim. For digital data created in the course of historic environment research and fieldwork in the UK the preferred archive may vary with respect to geographical area and historic circumstances.

  • In Scotland Historic Environment Scotland is the designated archive for all fieldwork records, including digital data, generated during archaeological fieldwork.
  • In Northern Ireland the Historic Environment Division (Department for Communities) Northern Ireland is the statutory depository for all records from fieldwork within the province.
  • In Wales the RCAHMW collects and curates archaeological records and archives (paper, photographic and electronic) within the terms of the National Monuments Record of Wales (NMRW) Collecting Policy. NMRW is the national repository for records of the archaeological, architectural and historic environment in Wales.
  • In England Historic England operates a selective archiving policy, all other archives are retained at local and county level.

The ADS works with the national heritage bodies, including ALGAO, to ensure that specifications for historic environment work include the obligation to offer an ordered digital archive for deposit. The ADS also works with the museums community, the Society of Museum Archaeologists and the Archaeological Archives Forum to ensure that museums make deposition with a recognised digital archive a condition of accepting historic environment archives. A list of local authorities and museums currently recommending deposition with ADS can be found on our partnerships page.

The ADS may be the only appropriate archive for digital datasets which encompass two or more of the constituent countries within the UK, or which relate to the UK as a whole (such as the CBA's Archaeological Site Index to Radiocarbon Dates from Great Britain and Ireland). Equally local, regional or national data creators may choose to provide access to their digital information through the ADS in order to contextualise it amongst other complimentary data resources and to take advantage of the opportunities of access to the scholarly community.

For secondary and analytical datasets, particularly research databases generated by those working in higher education (including databases created by research students) the ADS may also be the natural place of deposit. Those funded by the research councils are recommended or required to offer their digital historic environment data for deposit with the ADS.

In addition, for research activity by British researchers working overseas, there are currently few alternative archives, although as such centres are established the ADS will seek to develop collaborative agreements with them (e.g. DANS in the Netherlands).

2.1.6. Paper Records

The ADS only holds digital information. The ADS is not equipped for the adequate archiving of paper-based resources and does not hold any paper-based historic environment archives; it may however, provide advice about the digitisation of archives. The ADS is committed to the linking of distributed paper records, artefacts, and other related materials through their documentation, and through the OASIS system.

2.1.7. Disposal of Data

The presumption within the ADS archive is against disposal of data once accessioned within the archive. However, in the rare instance when disposal of data is thought appropriate, agreement will be sought from members of the ADS Management Committee and every effort will be made to contact the original depositor to inform them of the decision and where possible return the data, or help find an alternative repository.

2.2. Collection Data Types

The ADS Collections comprises the full spectrum of historic environment material, irrespective of data type. Such a policy enables the accessioning and delivery of multi-media datasets and allows an integrated digital archive. The decision to undertake such a wide-ranging collection policy was supported by the results of the ADS User Needs Survey, Strategies for Digital Data.

The ADS has substantial holdings of certain data types and currently collects all of the following historic environment data types when accompanied by the relevant metadata and deposited in an accepted format:

2.2.1. Electronic Texts

The ADS will maintain electronic versions of published journals, books, and monographs, and unpublished 'grey literature' fieldwork reports and provide free, open access to these resources via the ADS Library. 'Grey Literature'

Consultation with our user community revealed a desire for access to unpublished evaluation reports. In response to this perceived need the ADS, in collaboration with Historic England and other funding bodies, has developed the OASIS system and associated ADS Library to ensure the wider and more systematic dissemination of this form of 'grey literature'. Electronic Journals

The ADS will seek to preserve the functionality of electronic journals, including text, images, and multimedia features. The ADS already provides the archival home to the journal Internet Archaeology.

The ADS also provides access and preservation for the detailed information formerly held in the fiche of traditional paper journal publications and provides a service whereby it archives and provides free online access via the ADS Library to national, period and local society journals. PhDs and Supporting Data

The ADS takes deposits of PhDs undertaken in UK universities in historic environment, archaeology and related subjects, along with supporting data. The ADS does not accept other postgraduate or undergraduate dissertations, unless these include datasets of outstanding re-use value. These are assessed on a case-by-case basis.

2.2.2. Bibliographic Finding Aids

In addition to the ADS Library, the ADS provides access to specialised electronic bibliographies, such as that of the Vernacular Architecture Group.

2.2.3. Databases

The ADS collects across the full range of historic environment databases, including primary finds and context data from archaeological excavations, as well as files supporting secondary data analysis and synthesis. Databases specifically developed to enable research activity and those derived from national survey projects are collected as a high priority. Environmental and artefactual databases are also seen as being of particular utility.

2.2.4. Geophysics Data

The ADS seeks to preserve raw data derived from all types of geophysical survey, as defined in the Guide to Good Practice.

2.2.5. Aerial Photographs

Where aerial photographs are held in digital format they may be deposited with the ADS. The ADS also seeks to archive air photo interpretations or transcriptions of crop marks.

2.2.6. Topographic Survey

Raw data files derived from topographic and contour survey are maintained so long as they are relevant and capable of being re-used. This category also includes techniques which often create exceptionally large datasets, including LiDAR, and 3D laser scanning, as well as techniques of underwater survey, including echo sounding and sub-bottom profiling.

2.2.7. Buildings Survey

Digital data derived from architectural survey may be deposited with ADS. The development of our Historic Buildings holdings is currently one of the ADS Five Year Strategic Priorities..

2.2.8. Visualisation

3D reconstructions, including computer-generated solid models, VRML, and other visualisations will be collected where it is feasible to maintain them and where they are considered to be capable of re-use and restudy or are seen as being of importance for the history of the discipline. In general the ADS will also preserve the data from which the model is derived, and sufficient metadata in accordance with the principles of the London Charter (2009).

2.2.9. GIS

GIS may comprise a number of the data types listed above, although their functionality may depend upon the interaction of these elements, and the maintenance of a map-base that is independent of the project archive.

2.2.10. Moving Images (audio and visual)

Where audio and visual data is held in digital form they may be deposited with the ADS where it is deemed feasible to maintain them and where they are considered to be capable of re-use and restudy. Such resources may be delivered as streamed data.

2.2.11. Still Image Collections

Raster and/or vector images that are to be deposited with and disseminated by the ADS should be accompanied with enough documentation. Large image collections should also have appropriate file naming strategies to enable search and retrieval mechanisms to be put in place. Such collections include representative images which accompany a project archive, and image resources with accompanying databases of descriptive metadata, often delivered as 'Special Collections' (see below). ADS will also seek to build up collections of images which are important for the history of the discipline, and those which would form a core resource for teaching and learning.

2.2.12. Software

The ADS does not usually collect applications software developed for archaeological usage, including teaching materials, unless it exists in a form that makes it viable for future use, and is essential to support the re-use of a specific data resource. Software is frequently hardware dependent, of only short-term interest, and is incapable of migration without substantial programming effort.

2.3. Criteria for Evaluating Electronic Datasets

There are certain classes of digital data, such as CAD files, relational databases and GIS, which must be preserved digitally in order to maintain their functionality. There may equally be other categories of data that may be disposed of on the basis that it is more cost-effective to re-digitise as the need arises. The ADS acknowledges that it is of considerable benefit to both depositors and users that there be an effective and rigorous process of peer review of materials proposed for accessioning.

Where questions arise about the suitability of a dataset for archive or its re-use potential is unclear, the ADS can refer to a Collections Evaluation Working Group drawn from its Management Committee to assist the ADS evaluate datasets and maintain the rigorous standards necessary for the effective development of a quality resource base.

Data resources that are offered for deposit to the ADS will be evaluated to:

  • Assess their intellectual content and the level of potential interest in their re-use.
  • Evaluate how (even whether) they may viably be managed, preserved, and distributed to potential secondary users.
  • Determine the presence or absence of another suitable archival home.

Whereas the first form of evaluation involves assessment of the content of a data resource, the second focuses more on data structure and format, and on the nature and completeness of any documentation supplied. The third evaluation criterion is intended to prevent duplication of digital archiving efforts within the historic environment community, and to preserve the integrity of existing digital archives.

Such evaluation is essential to determine how best to manage a digital resource for the purpose of preservation and secondary re-use, and also to determine what costs may be involved in accessioning and migrating the digital resource. A dataset that does not meet all these criteria may not necessarily be rejected, particularly if it has significant re-use value. Instead, documentation accompanying such datasets will be modified to warn users of potential pitfalls.

2.3.1. Assessing Intellectual Content

The ADS seeks to accession high quality material which will facilitate future historic environment research or which preserves a primary record of past archaeological work. A review process ensures that the content of datasets is of the highest intellectual quality: collected and recorded according to accepted archaeological standards. Assessing 'quality' is a subjective exercise and in this the ADS will be guided by the following principles:

2.3.2. Evaluating Preservation Potential and Re-use Value Re-use Value

While some material may fit the needs of a particular project, institution, group of students, or other body, ADS datasets must have a wider applicability to the historic environment community as a whole. An assessment of re-usability must therefore be a key evaluation criterion.

The re-usability of datasets is largely determined by community needs. Inevitably requirements continue to change and consequently the assessment of user needs forms an ongoing part of the activities of the ADS. The ADS monitors requests from potential data users and actual demand for datasets to inform the process of determining re-use value.

Re-use value is also determined by the formats in which data are stored. If proprietary software packages form the basis of data entry/retrieval, and a majority of archaeologists do not have access to these proprietary systems, the dataset may be ranked low on the re-use value criterion. Adequate Documentation

The quality of datasets will be affected by whether or not they are accompanied by an appropriate level of documentation. This documentation should relate to both the content and the technical format of the resource.

DDocumentation provides important detail about the context in which data was created and maintained before archiving, and about the relationships between the dataset and other information sources. Suitability for Digital Preservation

If the format in which a dataset is stored means that the digital resource is irrecoverably obsolete upon presentation to the ADS this will be sufficient reason for recommending that the dataset not be accessioned.

2.3.3. Determining need of Primary Archival Home

There is no need to duplicate digital archiving services. If a dataset is being curated by an accredited organisation other than the ADS it will not be given high priority for accessioning. If a resource, however, is deemed to be of particular value to its user community, the ADS will seek to enter into a partnership with a collaborating agency in order to provide access to it. This may be at Served collections level and in such cases duplicate datasets may be accessioned into the ADS catalogues.

2.3.4. Inter-disciplinary Resources

The ADS will also provide a home for datasets from allied disciplines that are of value to its user community, regardless of their disciplinary origin. These may include numismatics, place-name studies, sculptural research, and aspects of manuscript studies. Material culture aspects of social and cultural anthropology are also included and, from within physical anthropology, the field of hominid studies and human evolution.

2.4. Acquisition Methods

The layered nature of the ADS Collection Policy necessitates data to be acquired by a number of means.

2.4.1. Archive Level Datasets

Archive level datasets will enter the ADS Collection by deposit under the ADS Deposit Licence. The ADS acquires and stores datasets produced by individuals, projects or institutions. This strategy is preferable in the case of fixed or static datasets. As a condition of acquisition, the ADS will negotiate the broadest possible assignment of rights to guarantee access and enable redistribution of the dataset. The ADS will negotiate a non-exclusive licence to distribute deposited data. Datasets with severe restrictions will be accepted only under exceptional circumstances.

2.4.2. Served and Brokered Datasets

Where appropriate the ADS will negotiate data exchange or access agreements with other organisations. These Served and Brokered datasets will ensure similar levels of data integrity and access as offered by the ADS in order to maintain consistency across the collections. It will also enable access to and/or distribution of datasets held in other collections.

2.4.3. Catalogued Datasets

Access to Catalogued datasets will also be provided. It should be noted the ADS only catalogues and links to quality resources of high utility to its user community and which have persistent URIs.

2.4.4. Licenced Datasets

While the ADS is unlikely to purchase or licence datasets directly, it may approach other bodies for funding to acquire a dataset of particular value.

2.5. Acquisition Strategies

Priorities for acquisitions will be defined by the ADS through its Management Committee, and through a continuous process of consultation with its user community.

2.5.1. Agreements with Co-operating Agencies

Where significant bodies of material are held by other agencies, the ADS may pursue Co-operative Agreements for the exchange of catalogue data and access to information, in preference to direct acquisition. The ADS will monitor the collecting activity and scope of other agencies to identify opportunities for collaboration.

2.5.2. Agreements with Granting Agencies

The ADS will seek to sign agreements with granting agencies that support humanities research, to encourage or mandate funding recipients to deposit their datasets. The ADS will seek to strike and sign such agreements with funding agencies that support research on the historic environment and related disciplines. The ADS will also seek to strike and sign such agreements with granting agencies that fund research exclusively or primarily in archaeology. The ADS will continue to work closely with all UK national heritage agencies. A list of the ADS current partnerships can be found on our partnerships page.

2.5.3. Acquiring Data from Individual (and Institutional) Depositors

The ADS will accession data from individual and institutional depositors. The ADS will inform depositors and potential depositors about the deposit process and provide guidance to them in appropriate forms.

2.5.4. Resource Creation

The ADS will enter into data creation projects where a significant resource is identified as missing. For example, the OASIS project provides index level data for all archaeological interventions and associated unpublished reports.

2.6. Rights Management

A Deposit Licence for use with individual and institutional depositors has been implemented to protect the rights of depositors, users and the ADS. Within this Deposit Licence the terms under which the dataset can be accessed and re-used is identified.

2.7. Payment

2.7.1. Payment for Acquisitions

While the ADS is unlikely to purchase or license datasets directly, it may approach other bodies for funding to acquire a dataset of particular value.

2.7.2. Receiving Payment for Services

The ADS implements a Charging Policy for the long-term preservation of a dataset or development of a bespoke interface as described in the Charging Policy. The Charging Policy recognises that digital archiving and bespoke interface design, entails significant expenditure and that these costs should be recovered from the body funding the data collection and/or research. Although ADS digital archiving pilot projects have indicated that basic archiving costs will add an overhead of less than 5% to the original project budget, more explicit statements of the costs are set out in the ADS Charging Policy. The Charging Policy will be implemented sensitively. The usage of ADS resources will continue to be supported free of charge.

2.8. Sensitive Data

Historic Environment and Archaeological archives may sometimes include sensitive, confidential or personal data which relate to identifiable individuals, but which may also provide valuable historiographical or contextual information of importance for an understanding of the context of data collection. The ADS wishes to preserve such data, and to make it available for research, learning and teaching. At the same time it recognises that this may raise issues of confidentiality and privacy covered by institutional ethics policies and possibly within the scope of the General Data Protection Regulation and the UK Data Protection Act 2018 and other legislation. The ADS has a policy and provides guidance on the deposition of sensitive, confidential and personal data.

2.9. Embargo Periods

When dealing with the archiving of digital data it is important that the data is archived (accessioned and ingested) at the point of deposit. This is to ensure that the data is in the correct format and accompanied by the appropriate documentation to ensure long-term preservation and sustainability. This does not mean that the data would be automatically accessible to the public. It may be deemed appropriate to establish an embargo period during which the data will be secured in the archive, but not accessible to the public. The length of the agreed embargo period will depend on the sensitivities involved.

3. Collections Management

Collections Management procedures and systems have been developed by the ADS which are recorded in our procedural policies and manuals. These are based on a framework of documentation and technical standards, and indicate target service (or performance) levels. The ADS has implemented a Collections Management System to track the progress of a deposit through the accessioning and preservation processes.

3.1 Documentation Standards

3.1.1. Shared Metadata for Information Discovery

In conjunction with bodies such as the UK Office for Library and Information Networking (UKOLN) the ADS identified a core set of resource description elements that may be applied to enable the development of an easily integrated catalogue. These core elements have been implemented by the ADS in describing resources in its collection. These have been enhanced by the addition of Library of Congress Linked Open Data subject terms.

3.1.2. Domain Specific Metadata

The ADS has additionally identified, documented, and adopted the richer level of resource description standards as appropriate for the resources in its collection. Including, but not limited to the Forum on Information Standards in Heritage (FISH) Thesauri vocabularies. The ADS Guides to Good Practice are also good sources of information about the creation of resource specific metadata.

3.1.3. Dataset Documentation

The ADS also maintains such detailed data documentation as may be required in the secondary re-use of resources in its collection.

3.1.4. Administrative Data

The ADS will document the administrative data it records about resources in its collection to enable the effective management of those resources through the implementation of its Collections Management System.

3.1.5. Data provided by Collaborating Agencies

Data held in the ADS catalogues includes that from other agencies received by the ADS under a Co-operative Agreement. As part of the definition of a Co-operative Agreement with another agency the ADS will be responsible for developing a concordance between data structures, and for managing the exchange of catalogue records.

3.2. Technical Standards

3.2.1 File Formats

The ADS Guidelines for Depositors sets out a framework of technical standards that define the file formats in which data will be accepted and stored. For specific deposit types these guidelines are augmented by the recommendations contained in the Guides to Good Practice series.

3.2.2 Network/Communications Protocols.

A framework of endpoints and metadata services has been implemented by the ADS. This includes interoperability with a number of European partners.The ADS is actively involved in the adoption of a service oriented approach to data aggregation and cross-searching.

3.2.3 Network Security.

A framework for maintaining the security and integrity of datasets and their documentation has been developed and implemented by the ADS. The ADS servers sits behind the University of York firewall, which controls the types of access to the data held on the server. At the point of delivery most of the information provided to users is presented as part of a dynamically generated web page that ensures the integrity of the underlying data source.

3.3. Collections Management System

The ADS has developed a Collections Management System that describes its holdings and centrally records descriptive, technical and administrative data.

4. Preservation

The ADS has implemented an archival system based on the Open Archival Information System (OAIS) for digital preservation. This is an ISO standard which determines the process of ingest, archive and dissemination for digital resources. The ADS first received the Data Seal of Approval as a Trusted Digital Repository in 2013 and is now a Core Trust Seal accredited repository.

5. Access and Use

The ADS encourages broad access to and use of its collections, both within the UK research community and beyond. The ADS actively develops opportunities to facilitate cross searches of distributed archaeological resources held by collaborating organisations, such as Europeana, the Ariadne Portal and MEDIN.

5.1. Data Use

The ADS has a dedicated post (Collections Development Manager), responsible for investigating ways of aiding and encouraging the use of its collections. These may include, but are not limited to, workshops, training events, lectures, and the development of Guides to Good Practice. If necessary, the ADS will support the design and development of tools to support data analysis, although it is unlikely to undertake development alone.

5.2. Rights Management

Access to the holdings of the ADS is free at the point of use to users for research and educational purposes. All users are required to abide by the Terms and Conditions of the ADS website and the appropriate access licence displayed in each archive collections. The ADS reserves the right to control the downloading of some or all resources by a system of user authentication at some point in the future.

5.3. Data Delivery Mechanisms and Tools

Data will be distributed to users via ArchSearch, ADS Archives and ADS Library.

5.3.1. Via the Searchable Catalogue of Metadata Records (ArchSearch)

ArchSearch has been developed to enable the searching of the entire ADS collections, as well as the collections of co-operating agencies. The principle underlying the ADS catalogue, ArchSearch is that archaeological data can be geo-referenced, inviting spatially based queries. Therefore we have developed cooperation agreements with the CBA, Historic England, Historic Environment Scotland, RCAHMW and DoCNI, and various local authorities and organisations which have provided us with over 1.4 million metadata records at site or monument level. These cover England, Scotland, Wales and Northern Ireland. Any site-based search within these areas will generally provide several hits pointing users to further resources. In specific cases, users can drill down from the site level metadata index record into a full digital archive held by the ADS.

5.3.2. Via ‘Project Archives’

Users are able to view online and download a variety of digital resources resulting from archaeological research, including excavation archives and artefact studies via the ADS Archives search facility.

5.3.3. Via ‘Special Collections’

The ADS have developed specific tools or working environments for the delivery and use of significant datasets including the development of map-based search tools accessed via the ADS Archives search facility.

5.3.4. Via ADS Library

The ADS Library has been developed to bring together material from the CBA’s British and Irish Archaeological Bibliography (BIAB), the ADS Library. of unpublished fieldwork reports as well as documents from the ADS archives and archaeological publishers such as Oxbow. Users are able to search over 300,000 bibliographic records for the historic environment, and when available link directly to the resource held by the ADS or by an external provider.