Preservation plan of EASY

This page contains the preservation plan of DANS’ EASY. For procedures on our Data Stations please refer to the Data Stations Policy.

The preservation plan outlines the principles steering the main activities of DANS regarding sustainable preservation of as well as access to digital research data for (re-)use within its user communities. From a preservation point of view the policy based on these principles generally conforms to those of FAIR as well as the OAIS Reference Model2, with alterations that are specific to the materials held within EASY,, the DANS core service for long term archiving (henceforth “the Archive”). The term “preservation plan” is taken from and in accordance with the CoreTrustSeal requirement R10 “Preservation Plan”: “The repository assumes responsibility for long-term preservation and manages this function in a planned and documented way”.

The basic principles of the preservation plan are outlined in Part I, chapters 1 to 8. This is the Preservation Strategy, being the general framework in which the data archive operates. Preservation decisions at the data archive are made within the context of the mission and strategy of the data archive, balancing the constraints of costs, scholarly value, user accessibility, and legal admissibility.

The preservation plan contains also the Preservation Policy as referred to in CoreTrustSeal requirement R9 “Documented storage procedures”, to be found in Part II, chapters 9-11. The Preservation Policy is the implementation of the principles outlined in the Preservation Strategy. It details the commitment to support the long-term management of data and also outlines the roles and responsibilities of all those involved in the collection and management of data. The preservation planning is discussed extensively. The goal of this OAIS function is to ensure that the data in the data archive remain accessible, understandable, and sufficiently usable over the long term. In chapter 10, Preservation Planning, it is indicated how this works out for DANS.

PART I Preservation Strategy

1. Scope and objectives of this plan

1.1. Scope of the plan

The scope of this plan is limited to the Archive: the DANS core service for long term archiving. It deals with all aspects of preservation and applies to all materials held by the Archive. This plan does not consider preservation of other materials such as DANS’s web pages, internal documents, and the Archive’s intranet. It also does not deal with other DANS services like DataverseNL or NARCIS.

The preservation plan follows a variety of external guidelines and standards for digital preservation such as OAIS, the FAIR principles, CoreTrustSeal (formerly Data Seal of Approval), nestorSeal (based on DIN 31644) and ISO 16363.

1.2. Objectives of the plan

The Archive’s primary objective is to identify, preserve and make available for use digital research data that have permanent or continuing value. The Archive assumes responsibility for the long-term preservation and accessibility of digital objects.

Most research data deserve to be kept available in the long term in order to be accessible for new research. DANS promotes sustained access to digital research data and encourages researchers to archive and reuse data in a sustainable manner.

In addition to possible reuse, data should also be kept available for replication and verification purposes. The Netherlands Code of Conduct for Scientific Practice (VSNU, 2014) prescribes a minimum retention period of ten years for raw research data. DANS does not consider ten years to be “the long term”; its oldest available data date back as far as 1964. In other words, after the minimum retention period data will remain accessible in the Archive.

The Archive is also responsible for ensuring the authenticity and integrity of the data. Any strategy for the long-term preservation of any digital information must address the issue of software dependence. For most digital information and in particular research data it is generally possible to eliminate software dependency. Thus the primary goal of the Archive’s preservation plan is to ensure the long-term accessibility of electronic information while ensuring the highest level of authenticity possible.

The specific aims of the preservation plan are to:

  • provide authentic and reliable instances of datasets to researchers;
  • maintain the integrity and quality of the datasets;
  • ensure that digital resources are managed throughout their lifecycle (e.g. when migrations or changes in metadata are carried out) in the medium that is most appropriate for the task they perform;
  • ensure that the relevant level of information security is applied to each dataset;
  • and so to be a “trustworthy digital repository”.

2. Mission of the Archive; content and designated community 

2.1 Mission 

DANS has as its mission to promote sustained access to digital research data. To ensure the continued use of these resources the Archive follows a policy of active preservation with the aim of ensuring the authenticity, reliability and logical integrity of all resources entrusted to its care while providing formats suitable for research for the long term. The designated community of the Archive consists predominantly of scholars in Humanities and Social Sciences.

The preservation plan codifies long-standing good archival practice at the Archive. In 1964 the first set of data has been archived by the Steinmetz Foundation for Social Sciences, one of the Archive’s predecessors. Another predecessor was the Netherlands Historical Data Archive (NHDA), founded in 1989. Furthermore, as of 2007 agreements have been formalised for archaeologists to deposit their data in the e-depot for Dutch archaeology (EDNA), which is now also part of the Archive. In the future the Archive may, gradually, extend its domains, in particular to Life Sciences.

The formulation and biannual revision of a preservation plan for the Archive are essential steps in fulfilling its strategic aims and responsibilities: it gives strategic direction both to continue initiatives, which are necessary for the management and protection of its collections, and to meet nationally and internationally agreed standards (to be) for digital preservation.

2.2 Characterisation of the content

The content of the Archive consists of digital research data, mainly from the humanities and the social sciences. The number of published datasets is around 40.000 (end 2017). The Archive acquires also data from other disciplines but at the moment this affects only a small part of the Archive’s holdings. The data collection is very heterogeneous in terms of data types, file format, size and usage. The data are generated for different purposes and through different processes. Not only the original data must be kept, but also the context that permits the data to be interpreted. This diversity adds complexity to the development of a preservation approach.

The Archive’s holdings consist of:

  • Data from the humanities: texts, spreadsheets, databases, images, transcripts (including time based transcripts), audio and video files and, more recently, graph representation of knowledge (linked data formats).
  • Data from the social sciences: mainly quantitative (statistical) data, questionnaires, codebooks, test responses and some qualitative datasets which include field notebooks, interviews and interview transcripts.
  • Archaeological data: reports, data from excavations and trial trenching’s and post-excavation analysis, such as texts, databases, spreadsheets, GIS files and images (vector and raster images).
  • Data from geospatial sciences: vector graphics, CAD drawings, GIS files.
  • Data from the life sciences and health research: images, statistical data, spreadsheets, databases, laboratory notebooks and texts.
  • Across those disciplines and beyond: Data in Linked Open Data formats, models, algorithms, scripts, executables.

A detailed list of data types and data formats in the Archive can be found in the list of “Preferred and accepted data formats” (See Appendix).

2.3 Community watch and dedicated services

The designated community of the Archive consists predominantly of scholars in the humanities and social sciences. The Archive monitors the community through substantial contacts, for instance during data acquisition and ingest, in applied research projects, membership of European Research Infrastructures, pilot studies with data producers, via training & consultancy and by offering discipline-specific services. The current section describes a selection of activities and services for specific communities, whereas chapter 11 “Recurring monitoring processes” provides an overview of generic processes for monitoring and improving the quality of the Archive.

A European Research Data Infrastructure ERIC represents the interests of a large, international, community. DANS participates in several Research Infrastructures: the CLARIN, CESSDA and DARIAH ERIC’s.

DANS has been designated as the service provider for the Netherlands in the CESSDA ERIC, which comprises the European national social sciences data archives. DANS is required to follow the CESSDA requirements on data and metadata. Currently, these are being detailed; DANS has not yet implemented (automated) assessment of social science data according to the relevant schema.

CLARIN provides access to digital language data collections across Europe and has introduced a dedicated metadata scheme, called CMDI. Whenever CMDI metadata are available for a dataset the DANS data archive provides them to metadata harvesters, with an extra metadata provider based on the OAI-PMH protocol.

DANS is also the Dutch coordinator of the DARIAH ERIC, a research infrastructure for the arts and humanities.

Together these infrastructures, with their national branches, enable DANS to stay in close contact with their communities, in particular on the data and metadata formats they prescribe.

Archaeologists in the Netherlands are required to deposit their data in the E-Depot for Dutch Archaeology, EDNA, which is accommodated at DANS. In order to make submitting data more efficient DANS has implemented the sector’s information exchange protocol SIKB0102. DANS has been involved in the development of this protocol. The metadata that the DANS data archive requires is automatically extracted from the “digital packing slip” (in Dutch also known as “pakbon”). Other advantages of adherence to the protocol are the uniform delivery of data and the possibility to link the data to other research information such as archaeological reports.

Dendrochronology is the scientific method of dating based on the analysis of patterns of tree rings. For researchers in this field DANS maintains the Digital Collaboratory for Cultural Dendrochronology (DCCD) repository.

Survey data are also the focus of Survey Data Netherlands, a more recent collaboration between Centerdata and DANS, which allows users to browse survey data from various repositories, including the data archive. Such browsing and analysing services on top of the data archive extend the dissemination functionalities of the data archive itself and help the community in deciding whether and how to reuse data.

DANS expects that, as broadening of EASY for other designated communities will take place in the future, more specific discipline-related (domain-dependent) metadata fields will be defined in EASY, notably within the framework of international research infrastructure projects in which DANS is involved.

For a number of datasets in EASY reviews are available. The intention is to introduce a revised review system, based on the FAIR principles. Citations to related works are provided in EASY as standard field in the DIP (Dissemination Information Package). EASY automatically generates the citation to the dataset concerned, following the Datacite model.

3. Requirements

3.1 The Archive’s requirements 

The Archive has developed a series of requirements which it strives to ensure as closely as possible:

  • the data that the Archive acquires are accompanied by adequate documentation to enable their use and re-use for analytical and research purposes;
  • the datasets are checked and validated according to strict data ingest procedures (see paragraph 9.2);
  • the data are professionally catalogued according to appropriate metadata standards;
  • the data, documentation, metadata and other representation information are preserved for the long-term;
  • the authenticity, integrity and reliability of datasets preserved for future use are retained;

3.2 Legal and regulatory framework

The legal and regulatory frameworks for the management of the data acquired by the Archive are as follows. As an institute of the Royal Netherlands Academy of Arts and Sciences (KNAW), DANS is not a legal entity in itself. Instead, the KNAW is the legal entity under which the Archive functions.

In preserving its datasets and providing access to them the Archive follows:

  • Dutch Data Protection Act (WBP), elaborated in the “Code of conduct for use of personal data in research of the Dutch Association of Universities” (VSNU, 2005). Both law and code of conduct will be replaced in 2018 (law) or possibly later (code of conduct);
  • Dutch Copyright Act (1912/2004);
  • Dutch Database Act (1999);
  • OECD Principles and Guidelines for Access to Research Data from Public Funding (2007);
  • Specified privacy regulations for treating personal data agreed with depositors, users or other third parties.

The relationship between the depositor of a dataset and DANS is based on a legally-binding deposit agreement and licence (known as the Licence Agreement) which

  • confirms the rights and obligations of both parties;
  • states that DANS shall ensure, to the best of its ability and resources, that the deposited dataset is archived in a sustainable manner and remains legible and accessible.
  • states that DANS has the right to modify the format and/or functionality of the dataset if this is necessary in order to facilitate the digital sustainability, distribution or re-use of the dataset.
  • states the conditions under which access may be given to third parties, as specified by the depositor (DANS applies the principle ‘Open if possible, protected if necessary);
  • states that the depositor has cleared all necessary permissions.

Depositors are asked to clear, possibly unresolved, rights of third parties on (parts of) the datasets at beforehand. DANS is not liable for the contents of the datasets made available through EASY, nor for the documentation associated with those datasets. DANS is also not liable for content errors or incorrect inferences from the datasets and the data contained therein.

The relationship between the user of a dataset and the Archive is based on legally-binding General Conditions of Use which concern

  • the use of the data;
  • the special restrictions that apply to datasets with personal data according to the Dutch Data Protection Act (WBP) or the General Data Protection Regulation and complimentary law (AVG and UAVG) as well as other relevant laws;
  • the required bibliographic reference to the dataset.
  • No content liability by DANS (disclaimer)

4. Roles and responsibilities

All DANS staff assist in implementing the policy contained in this preservation plan as appropriate to their roles and responsibilities. The Director is responsible for maintaining this policy.

All DANS staff, including temporary staff, trainees, visiting fellows and volunteers, are accountable for keeping up confidentiality when processing data, in particular personal data, in any way whatsoever, by signing the “Declaration of Confidentiality DANS for employees”.

5. Content coverage 

Research carried out within the designated community yields a wide range of data types such as texts, spreadsheets, databases, pictures, video, audio, and geographical information. The Archive strives to accommodate this wide range of data types. For any data type various digital file formats exist.

However, all formats of digital files stand the risk of becoming obsolete in the future. The current software will not be able to represent and use the content of the file in the way it was meant to at the time of creation. Moreover, software may be dependent on hardware and the Archive is not in the position to preserve hardware. However, some precautions can be taken. One such measure is to select file formats that have a high chance of remaining usable in the far future. Therefore the Archive has assessed a number of file formats resulting in a list of preferred formats and acceptable formats.

The preferred formats are the file formats which the Archive trusts to offer the best long-term guarantees for usability, accessibility and sustainability. Data depositors are strongly recommended to deliver their data in the preferred format corresponding to the type of data. The Archive also allows the use of acceptable formats, but informs prospective depositors about the fact that long-term preservation of these formats is uncertain. This list of preferred formats and acceptable formats changes over time as new formats will be developed and others will fall into disuse.

The data files that the Archive intends to acquire, preserve and make available are of a static nature, i.e. they are not work “in progress” anymore. When data are changed or extended, the resulting updates are considered as new datasets.

Until now the Archive does not acquire or preserve the software programs that has been used to generate research data, although researchers are encouraged to deposit documentation of the applied software (such as brand, version and configuration parameters) in conjunction with the data.

6. Properties to be preserved 

The list above illustrates that a single data type, for instance a GIS file, may be used in several academic disciplines. The significant properties of a data type, however, may vary according to the discipline in which it is used. This implies that, in order to define what should be preserved, for each data type the ‘intended use’ of the designated community must be established. Recently the Archive has begun to describe significant properties of data types more explicitly.

7. Integrity and security

The complete chain of the Archive’s custody of all datasets is documented through metadata. All actions are explicit, complete, correct and current. However, only the „original‟ version can be said to be an integral copy of the version deposited with the Archive. The preservation and dissemination versions are considered to be authentic and there is provenance information of all alterations in the preservation and dissemination versions that relates back to the original deposited version.

The Archive is committed to taking all necessary precautions to ensure the physical safety and security of the data it preserves. This includes a periodical technology vulnerability scan, the SLA with the data storage provider, a procedure for file fixity checking, the Declaration of Confidentiality for employees and a periodical safety inventory by the KNAW.

8. Sustainability plans and funding

To fulfill its mission the Archive receives structural lump sum financing from both the KNAW and Netherlands Organisation for Scientific Research (NWO). It is explicitly stated in the “NWO-KNAW Collaboration Agreement DANS” (Samenwerkingsovereenkomst) between NWO and KNAW that NWO and KNAW in the case of discontinuity of DANS will take over the responsibility for the data files archived at DANS and store these elsewhere “in the most responsible manner possible and under equivalent technical conditions” (article 10.6 of the Collaboration Agreement 2015).

Institutional depositors, as opposed to individual researchers, constitute another source of funding, as does participation in national and international data-infrastructures as well as research and development projects. This follows from goals in the DANS Strategy Policy.

PART II Preservation Policy

9. Implementing the preservation strategy

The following chapters are structured around the main functional concepts of the Open Archival Information System (OAIS) reference model for digital preservation environments as well as the FAIR principles. Preservation decisions at the Archive are made within the context of the Archive’s mission and strategy, balancing the constraints of costs, scholarly value, user accessibility, and legal admissibility. The Archive’s processes are organised according to this model.

9.1. Pre-ingest function

Officially, the pre-ingest function is not part of the OAIS model. However, the Archive has learned from experience that pre-ingest services help to ensure the usability and accessibility of datasets through the improved quality of metadata and documentation. This way, they also reduce costs within the ingest phase.

In particular, the Archive provides data guides, training and consultancy to groups and individuals about issues such as data formats, data management plans and legal issues.

9.2. Ingest function 

Ingest is the first functional component of the OAIS reference model. It includes the receipt of information from a producer and the validation that the information supplied is complete. This process also identifies the specific properties of the information which is to be preserved; it authenticates that the information is what it purports to be. The Archive is a self-deposit system, as a principle: the data producer him- or herself is responsible for successfully documenting and depositing the data.

The Archive staff performs quality control by following a data processing protocol to safeguard that the supplied data will be findable, accessible and comprehensible for the long term.

The version supplied by the data producer is known within the Archive as the “original‟ version and this is retained for preservation in its original format and stored in the appropriate directory on the preservation system. This supplied version has a close correspondence to the Submission Information Package (SIP) in OAIS terms.

Additionally, during the archival procedure, an archivist may convert files to preferred formats to ensure long-term preservation and accessibility.

Only the approved/curated data and metadata will be published. If the data and metadata required transformations, then the original data are kept, but not published. If files are migrated, the migrated files will be published with the dataset for use. The depositor will become aware of these changes when the dataset is published. An archivist may apply minor changes to the metadata or the directory structure. Larger issues will be consulted with the depositor.

Upon submitting the original version the depositor is informed that the material has been transferred to the Archive’s custody. When the Archive staff has subsequently processed the dataset and it has been accepted by the Archive, then the dataset is published and the Licence Agreement is sent to the depositor along with the unique persistent identifier minted by the Archive’s system.

The version resulting from the ingest process is an Archival Information Package (AIP). All actions related to the preservation of the data are documented in the DANS Provenance document.

Increasingly, datasets are ingested in a almost fully automated way by ftp, SWORD or other way. This applies in particular to datasets being ingested on the base of a collective contract with a data supplier.

9.3. Archival storage function

In essence, the purpose of archival storage is to ensure that what is passed to it from the ingest process remains identical and accessible. In the Archive this function receives AIPs from the ingest function and adds them to the permanent storage facility, oversees the management of this storage, including media refreshment and monitoring. This function is also responsible for ensuring that AIPs can be retrieved.

Data storage management has been outsourced. The Archive has a Service Level Agreement (SLA) with its data storage management provider, which includes a confidentiality statement.

9.4. Data management function 

Data Management is the third major function of the OAIS reference model. It maintains databases of descriptive metadata; supports external finding aids; and manages administrative metadata which support internal operations, including change control.

Ensuring that any alteration to the preserved version of any part of a dataset is accurately documented is integral to the authenticity of any dataset. The Archive distinguishes between two forms of alteration post ingest:

  • New version and therefore a new dataset: when there is a change to data;
  • Minor change: when there is a change to metadata, descriptive documents or supplementary files.

A new version is deposited as a new dataset and will therefore receive its own persistent identifier. The new and the previous dataset are cross-referenced in their respective descriptive metadata. Alternatively, when there is a minor change, this change is documented in the administrative metadata; no new persistent identifier is minted.

In the case of data conversion to another file format for preservation or access purposes, the Archive maintains the original file(s). The conversion aims to preserve the content of the data, because this is seen as the most significant property of the data. Preservation of other aspects, such as the layout of the input format (the “look and feel”) is considered to be of lesser importance for most research data.

Deleting data would be an extreme case of data change once published. In principle however, in principle the Archive does not delete published data, unless sufficiently weighty grounds exist for removal.

9.5. Access function 

This OAIS function contains the services and functions that make the archival collection and related services visible to consumers. End users interact with the Archive to find, request and receive datasets. By default these processes are web-based, but with support by the Archive staff.

Apart from the processes that support these three activities (i.e. find, request and receive datasets), the access function also implements the security that is related to access.

To enhance findability, metadata is checked and completed where necessary and collaborations enabling metadata enhance the findability of the content of the archive. The map feature enables users to locate datasets on a map through their coordinates.

9.6. Administration function 

In the OAIS model the administration function manages the day-to-day operations of the Archive. Processes covered here e.g. relate to the negotiation of the license agreement and the general conditions of use and to system engineering functions to monitor the Archive’s system operations (see paragraph 9.3).

10. Preservation planning

Several services and processes in the Archive’s organisation relate to what is known as “Preservation Planning” in the OAIS reference model.

Figure 2 Functions of the Preservation Planning Functional Entity in the OAIS model (Reference Model for an Open Archival Information System (OAIS), Recommended Practice, CCSDS 650.0-M-2 (Magenta Book) Issue 2, June 2012. Figure taken from page 4-14).

10.1 Preservation principles: FAIR

DANS aims to operate according to the FAIR Guiding Principles in making its data in The Archive FindableAccessible, Interoperable and Reusable. Below is described, per principle, how the data comply.

To be Findable 

  • Each dataset deposited in The Archive is automatically assigned a Digital Object Identifier (DOI) and a URN:NBN identifier to facilitate discoverability and sustainable reference.
  • THE ARCHIVE Metadata, an extension of Dublin Core Terms (dcterms), are quite rich with regard to machine-readability. They can be exported through the user interface in XML and CSV formats so as to be discoverable by both humans and computers.
  • Furthermore, the entirety or a selection of EASY Metadata records can be harvested through its OAI-PMH service, which also makes datasets more visible to providers of search and discovery services.

To be Accessible 

  • Metadata (defined as: the content of all fields displayed with the dataset under the ‘Description’ tab in EASY) in EASY are without copy- or database-rights and always openly accessible – no authentication nor authorisation is ever needed – either through the user interface or by using the open and universal OAI-PMH protocol.
  • To access datasets in EASY new users are requested to first create a user account through registration (authentication). Open data are usually accessible after login into the system, while for restricted data users need to request permission by the depositor of the data (authorisation). Authentication by registration is not obligatory for downloading or using data in the access category Open Access (CC0 Waiver).

To be Interoperable 

  • EASY Metadata are mapped to Dublin Core Terms – a formal, accessible, shared and broadly applicable language for knowledge representation. Nevertheless, to comply to the needs of other partners, DANS maps and exposes the EASY metadata to other metadata schemas such as DataCite, DIDL, Carare and ACDM.
  •  To facilitate interoperability to a greater degree, the below listed controlled vocabularies are used for the metadata in EASY:
    – Archaeological Basis Register (ABR) thesaurus
    – Narcis Classification
    – Contributor Information (Datacite 4)
    – ISO639 (language)
    – W3CDTF or ISO8601 (date)
  • To indicate any relations with other resources of any type and add value to the data, the Dublin Core “Relation” element is used for the metadata in EASY. All properties of DC terms that can indicate relations with other sources are possible (eg. IsVersionOf, HasVersion, IsReplacedBy, Replaces, IsRequiredBy, Requires, IsPartOf, HasPart, IsReferencedBy, References, IsFormatOf, HasFormat).

To be Reusable 

  • Depositors are encouraged to describe their data with as much detail as possible. The EASY metadata contains 17 Dublin Core Elements. Six elements are obligatory: Title, Creator, Description, Date (created), Rights, Audience. The required elements richly describe the data’s provenance information; what are the data about, by whom and when they were created as well as how the data were created and for which purposes.
  • To enable proper reuse data in EASY are always released with clear conditions of use.
  • Having recognised the need to lower the barriers and facilitate data reuse by different communities, DANS implements some measure of interoperability among different metadata standards which are exposed through its OAI-PMH service. DANS is committed to use both domain-specific and domain-neutral metadata standards when necessary.
  • Once a dataset is published only DANS can make changes, keeping control of the authenticity.
  • Fixity checking is in place, verifying that data have not been altered or corrupted.

11. Recurring monitoring processes

This is an overview of processes in the Archive’s organisation which contribute to Preservation Planning, because they monitor community, technology, legal or strategic developments or risks.

Nr. Process Frequency Responsible

Monitor the Archive’s designated communities for developments that may affect the Archive, such as – requested – changes in the technology or the file formats that communities use.

This is done in substantial – not always plannable – contacts with the communities, e.g. in data acquisition, applied research projects, membership of European Research Infrastructures, pilot studies with data producers, and training & consultancy.

Furthermore the Research & Innovation department (R&I) contributes to this monitoring activity, both supply-driven (from R&I to the Archive) and demand-driven (from the Archive to R&I).

Daily coordinator Archive + Coordinator Research & Innovation

Check whether all the Archive’s preferred file formats should still be preferred and whether the list is complete (given mission and scope of the Archive). If not:

  • Analyse alternative formats and select a new preferred format;
  • Migrate all relevant files from the no longer preferred format to the successor format conform the DANS preferred file formats guidelines;
  • Update the relevant internal & external documents
On a regular basis Preservation Officer + “Preferred Formats” Internal Working group
3 Check the potential impact on the Archive of – expected – legal and/or regulatory changes, including codes of conduct, also with regard to personal data Continuously Legal Advisor

The Archive systems are monitored.

The monitoring is done by DANS ICT support and by the external service and storage providers. When a malfunction is noticed the corresponding action will be executed.

Continuously Coordinator IT Support
5 Monitor potential external threats to the IT network Continuously, plus annual update of the security policy, initiated by KNAW/I&A Security Officer
6 Revise this Preservation Plan: still up to date or is there reason to change (either of) it? Are there any unintended consequences of revision that must be taken care of? Biannually Coordinator Archive
7 Update the DANS multiannual strategy, including the services (archival and otherwise), strategic goals and designated communities Every four-five years Director DANS

Appendix: References

(All url’s checked May 2018). DANS’s documents on policy and strategy .

Other references