3.3.1. Participation in research data networks

As described in the sections below, it appears that participation in national, regional, as well as subject-specific networks has generally shaped the repositories’ infrastructure, particularly in the ways that their adoption of harvestable metadata services has developed or is being planned for development.

All of the studied repositories have been guided or supported by a larger entity while developing harvestable metadata services: INTERMAGNET and ISGI have participated in the European Open Science Cloud’s (EOSC) EPOS ERIC project, while WDC-RRE, NSSDC and GCdataPR have developed with support from Chinese research data institutions. One of the data sources for the GCdataPR comes from cooperation with journals for enabling discovery. GCdataPR initiated a tri-journal program since 2015 to facilitate dataset publication, data paper publication and science discovery publication. The three journals worked closely with authors to publish discovery papers as well as datasets and data papers. Finally, both SEDAC’s and IGS’s infrastructures have been supported by the National Aeronautics and Space Administration (NASA) EOSDIS community, and their extensive collections of knowledge and technical resources.

Geomagnetism data in Europe: the EPOS ERIC. Within the European geomagnetism community, the European Plate Observing System European Research Infrastructure Consortium (EPOS ERIC) has played a major role in promoting the uptake of 21st century technologies and standards to create more granular and robust metadata and dataset documentation (Chambodut et al. 2018; Flower and TGS Geomagnetic Observations 2019). Following EPOS ERIC’s leadership, ISGI plans to migrate the repository’s metadata records into an interoperable schema that will allow repositories to serve metadata to European aggregators like OpenAIRE. Currently, ISGI is considering implementing CERIF, DataCite, and/or DCAT compliant metadata. Since 2013, INTERMAGNET has been publishing yearly definitive data through the GFZ (GeoForschungsZentrum) Data Service, which serves dataset metadata to aggregators using various metadata standards and sharing protocols. Furthermore, a metadata development project is underway to gather metadata for all observatories recording geomagnetic data worldwide. This includes the INTERMAGNET geomagnetic observatories metadata combined with metadata records held by the WDC for Geomagnetism, Edinburgh.

The Chinese research data infrastructure. GCdataPR, NSSDC and WDC-RRE were among the original Chinese data repositories that joined the ICSU system of World Data Centers in 1988. In 2008, to promote collaboration between the eight Chinese repositories at the WDS, the WDS China Common Clearinghouse was created (Wang et al. 2020). The prototype for the WDS China’s unified metadata search portal was constructed with Pycsw, a Python implementation of the OGC’s Catalogue Services for the Web (CSW) specification (Wang et al. 2020). This initiative, led by WDC-RRE, encouraged and supported WDS members to develop harvestable metadata services based on similar spatial data interoperability standards, notably ISO 19115/19139/19119 metadata and the OGC CSW protocol.

Outside of the WDS, the Chinese repositories contribute to the larger Chinese digital research infrastructure, as part of 20 Chinese Data Centers organized under the National Science and Technology Infrastructure Center of China.¹⁸ The 20 national data centers provide their metadata collections on a regular basis to a unified metadata search portal operated by the National Science and Technology Data Sharing Network of China (National Science and Technology Infrastructures 2016). These records must comply with the Chinese Science and Technology Infrastructure Resource Core Metadata standard (GB/T 30523-2014, China National Institute of Standardization 2014). Furthermore, all metadata records held by the 20 national data centers, including NSSDC, must be registered in accordance with the Science and Technology Resource Identification (CSTR), GB/T 32843-2016 (China National Institute of Standardization 2016), so that these metadata records can be discovered in the CSTR Identification platform. Another class of the data repository is peer reviewed dataset publications through the digital journal. The Global Change Data Repository is a digital journal (ISSN 2096-868X), which is issued monthly and compatible with the Journal of Global Change Data & Discovery (ISSN 2096-3645), a journal for publishing data papers. The two journals and the data and knowledge hub (metadata based links for specific applications) are part of the Global Change Research Data & Repository (GCdataPR). Through its publication methodology and procedures, the GCdataPR maintains long-term preservation and public availability of timely, quality and informative datasets. Both WDC-RRE and NSSDC also maintain custom metadata profiles that integrate local and international interoperability features. In addition, the China National Knowledge Infrastructure (CNKI) also is aggregating metadata from GCdataPR and WDC-RRE.

EOSDIS at NASA. Two of the repositories, SEDAC and IGS, are (at least partially) based in the United States, and they receive support from the National Aeronautics and Space Administration’s (NASA) infrastructure. As one of NASA’s Distributed Active Archive Centers (DAACs), SEDAC participates actively in initiatives stewarded by the Earth Science Data and Information System (ESDIS) project and SEDAC metadata is provided to NASA’s EOSDIS Common Metadata Repository (CMR). The CMR is the back-end of Earthdata Search, the Global Change Master Directory (GCMD), and the International Data Network (IDN), the latter of which transfers SEDAC metadata into GEOSS. The complete collection of IGS data, which is distributed across data centers, has one of two complete mirrors hosted by a NASA EOSDIS data center, the Crustal Dynamics Data Information System (CDDIS) (the second mirror is hosted by the European Space Agency).¹⁹ Thus, at present, metadata records for SEDAC datasets and for IGS collections are served in metadata search/retrieval endpoints at the CMR (Noll and Michael 2019), and they are available in multiple established metadata formats, specifically: DIF 10, ECHO 10, ISO 19115-2:2009 (MENDS and SMAP dialects), and UMM-C (Reiter and llincione 2019).

4.1.1. New users, new challenges

As a repository shares data more widely, its users become more diverse and heterogeneous. Catering to these evolving user needs is one of the most salient challenges faced by the HMetS-WG data repositories.

ISGI and INTERMAGNET provide good examples of how users’ growing diversity may pose challenges to repositories, even those with well-established data-sharing cultures. Open Data and sharing have always been essential for the geomagnetism community, as earth-observation research can rarely be done without data from multiple countries. In fact, geomagnetism’s established data-sharing tradition is evidenced by over 50 years of collaborative data practices which have included yearly data publications and established, shared standards; e.g. the IAGA2002 data Exchange Format (2016). At INTERMAGNET, participants are volunteer magnetic observatories which, following standards defined by the network, seek to share and confidently reuse geomagnetic data within the community. ISGI’s participants, in contrast, are institutes whose official task is defined by the International Association of Geomagnetism and Aeronomy (IAGA): to derive and make available officially endorsed data products. In recent years, the geomagnetism community has sought to achieve interoperability with other scientific fields of Earth and environmental observation, and to keep up with current trends to make data more usable, and also more useful, to a larger group of users, not only geomagnetism specialists. As we shall see below, both organizations have needed to factor in these developments when selecting their data and metadata sharing technologies.

Post-Pandemic, data driven regional economic development efforts involve new challenges, especially in rural areas, mountain regions, and small islands. In order to help such regional stakeholders, including decision makers and small business companies, GCdataPR initiated the Geographical Indications Environment & Sustainability (GIES) program. By opening quality datasets, data papers, and metadata (physical geographical data, agriculture products data, socio-economic data and local culture information, as well as in situ timely ecosystem monitoring data), the geographical indications or specific agriculture products could be used by consumers. The GIES cases clusters and practices demonstrated this as an effective solution for the repository to serve local people in attaining the 2030 Sustainable Development Goals (SDGs) (Liu, Gong & Liu, et al. 2021).

4.1.2. Stakeholder engagement, user outreach, adaptation of services

The repositories in this study have shown a clear user orientation, and most report an intent to serve diverse user communities: from the general public to industry data users, to researchers in highly specialized knowledge areas (see Table 2). Concerted outreach is regularly carried out among multiple groups of users and stakeholders, including current and potential users. Also, without exception, each of the repositories participates actively in sundry working groups and opportunities to exchange knowledge, within grassroots, top-down, or federated organizations. Some of these include the WDS, the Research Data Alliance (RDA), and the International Science Council’s Committee on Data for Science and Technology (CODATA), the American Geophysical Union (AGU), the European Open Science Cloud’s (EOSC) EPOS ERIC, the Group on Earth Observations (GEO), China-GEOSS, and the ESDIS system at NASA.

At IGS, for example, data services are being developed to meet the needs of new and established users (Ventura-Traveset, Navarro & Romero 2019), such as those found within IGS itself, including product coordinators, participants in working groups and pilot projects or in analysis centers, (Villiger & Dach 2019a: 139). But because all users of modern mapping, orientation and navigation systems are beneficiaries of the work done by IGS, the IGS Central Bureau has established various channels for outreach and communication (ibid.: 18), with the public and individuals, enterprises, non-profits, institutions and government actors worldwide. These channels include social media outlets like Twitter, where IGS uses the #GNSS4impact hashtag to tweet about common applications of GNSS data. Part of the aim is to make the general public aware of this foundational yet invisible infrastructure. Making IGSs work visible to the general public in ways that can be measured – such as through citation of IGS data, products, and other published outputs – helps IGS advocate for the organization and make a strong case to its supporting partners and funders (IGS Central Bureau 2023).

Repositories also will need to adapt the metadata that they distribute to address the current needs of the user communities that they serve as these needs change. In addition to revising repository services offered, such as recommended uses and data formats and the like, it may be necessary to adopt metadata standards and enhance metadata harvesting capabilities to reflect the knowledge and research interests of the new community segments and domains that are being served. For example, a repository may discover changes in the disciplines of its users by identifying the disciplines of publications and authors that are currently citing the repository’s data holdings. Learning about such changes can enable the repository to identify additional metadata standards, particular metadata elements, specific vocabularies and harvesters that can serve the needs of the new communities as the disciplines of users change. Recent developments, such as those described by Musen et. al (2022), include metadata templates, discipline-specific ontologies, and metadata evaluation software tools that enable rich FAIR-compliant metadata to be produced for distribution to particular communities and across communities of data users.

4.1.3. Repository usage metrics and citation counts

To some extent, repositories can keep track of their efforts to increase data discovery and, ultimately usage, through counters that measure user engagement with repository assets (e.g. clicks, downloads, searches, turnaways), which can help keep track of fluctuations and patterns in a repository’s engagement and usage. A current standard for repository metrics is embodied in the COUNTER Code of Practice (Fenner et al. 2018). Some repositories, such as NSSDC and SEDAC employ a simple user authentication requirement, via a single log-in or registration with an e-mail address, to gain insight into data usage patterns beyond raw metrics, shedding light onto the frequency of usage for each item and the types of users who may be accessing data assets. In contrast, GCdataPR reports using IP addresses and real-time usage statistics to keep track of the repository’s international visits, in a way that is consistent with GCdataPR’s stated goal of reaching a broader international user base. But, while potentially useful for tracking users’ online interactions with the repository, these alternative metrics also have limitations as indicators of actual dataset reuse (Ramachandran, Bugbee and Murphy, 2021).

Alternatively, data citation tracking, despite its limitations,²¹ is increasingly becoming a tool that can be used to estimate the scientific impact of a repository’s data assets and to facilitate some types of bibliometric analysis of data usage. Among our use cases, GCdataPR, SEDAC and WDC-RRE report tracking data citations. SEDACs platform has also implemented a searchable online database that contains references to citations of the repository’s datasets (Socioeconomic Data and Applications Center 2023a).

4.2.1. Sustainable growth and operations

In research organizations without a strong culture of research data management (RDM), it may take time to build support for expanding data services with initiatives such as a new metadata service. For example, the Göittingen eResearch Alliance (Dierkes & Wuttke 2016) built institutional support by engaging with the organization’s key decision makers and stakeholders. Alternatively, SEDAC and the three WDS members in China have been able to build support for their data centers within their host institutions and their national data infrastructures, and this is reflected in the repositories’ maturity status. These examples also underscore that collaboration among community stakeholders fosters efforts to attain data repository interoperability, as reported by Gries et al. (2018).

For less hierarchical organizations like research networks and data federations, the most salient challenges involve coordinating the development of a common standard or application profile, or coordinating the adoption of an existing technology (Yarmey & Baker 2013). The two WDS network members among our use cases, IGS and INTERMAGNET, are different examples of established, international data federations that managed to create impressive infrastructures on the basis of voluntary member participation, through many decades of collaborative work.

The voluntary, federated character of IGS relies on decentralized funding schemes for projects and initiatives, usually by public institutions, governments or other research organizations. To maintain its reliable service provision, IGS must rely on system redundancy and on multi-year support commitments from the institutions that host the key elements of the system (IGS Central Bureau 2023; Villiger & Dach 2019b). To marshal support for a project, repository partners have to be able to envision the positive and tangible ways in which the project will impact funding partners and their constituencies, and how it will benefit the institution and society as a whole. In particular, IGS public outreach and communication initiatives reflect the organizations keen understanding of that fact.

4.2.2. Resource constraints

It is also useful to bear in mind that open-source software (OSS) is being produced and made available on a regular basis, some of which is intended for repositories to implement harvesting protocols with lower investment costs. For example, harvesting protocols can be implemented as modules in bespoke repository platforms by means of Viringo, an OAI-PMH API created by DataCite and further developed at FRDR, or Pycsw, a Python implementation of the OGC CSW protocol that is used by WDCRRE for its Catalogue Service. A minimal implementation of harvestable metadata may consist of a web-accessible folder (WAF), sitemap, or publicly accessible XML file of machine-readable metadata.

While a discussion of the advantages and disadvantages of OSS lies outside of the scope of this paper (see Trappler 2009, for a discussion of OSS pros and cons), it bears mentioning that repository managers will need to weigh the benefits of OSS against potential trade-offs (e.g. increased labor costs, community vs. corporate support services, etc.). Nevertheless, software solutions implemented with OSS may offer advantages for adoption if technological compatibility and software reusability is possible.

Independent of the decision to select a particular approach for implementing an enhancement, such as harvestable metadata capabilities, additional sources of support may be needed to sustainably develop and deploy improvements to data repository infrastructure. If the costs of enhancements are not absorbed by operating budgets, such costs may need to be supported separately. In such cases, data repositories may need to initiate projects and secure additional support for improvements to their services as part of their approach to providing sustainable data stewardship (Downs & Chen, 2016).

4.3.1. Metadata and open data access policies

In general, repositories may be hesitant to expose metadata for protected datasets and/or collections. Although none of our repositories reported hosting private or confidential data, some assets in the NSSDC repository are embargoed for a short time period, which is deemed long enough to ensure that data owners’ rights and interests are protected. NSSDC’s approach is compatible with the requirement that data be as open as allowable, but as restricted as necessary. SEDAC favors the use of open data licenses (mainly CC BY 4.0),²² ‘unless there are extenuating circumstances such as data restrictions inherited from input data’ (Socioeconomic Data and Applications Center 2023b). Wherever relevant, necessary consideration must also be given to data sharing practices and principles – beyond FAIR – that focus on various ethical concerns, such as the First Nations Principles of OCAP (First Nations Information Governance Centre 2014), and the CARE Principles for Indigenous Data Governance (Carroll et al. 2020). This means investing in the technical solutions that embody those principles: differentiated access policies and secure data storage, with trustworthy capabilities for offering selective data access under distinct protection classifications; or providing access only to authorized users. Machine-readable data licenses in metadata (Creative Commons 2002) can instruct search engines and automated software to display and filter content according to their licensing, which can in turn remind users of the freedoms and obligations (e.g. proper attribution) associated with the dataset.

4.3.2. PIDs, DOIs, and identifiers for dynamic datasets

Persistent, unique identifiers (PIDs) for digital objects can enhance and enable a range of interoperability features, from automatic metadata retrieval for bibliographic references in tools like RefWorks and Zotero, to deduplicated aggregation of dataset metadata into federated catalogues, to the analysis and visualization of networks of scholarly communication and collaboration like OpenAIRE’s Research Graph (Manghi et al. 2019). The Digital Object Identifier (DOI) standard (Paskin 1999), which emerged in the 1990s, as well as newer PIDs like the Research Organization Registry (ROR)²³ and Open Researcher and Contributor IDs (ORCID)²⁴ have opened new avenues for automating links between metadata records, and for creating new digital research services. The growing use of the ROR identifier in dataset metadata is a case in point. Since implementing ROR tags in 2020, national aggregation platforms like the Federated Research Data Repository (FRDR) have the option to selectively harvest Canadian data from non-Canadian repositories when at least one of the authors is affiliated with a Canadian research organization (Digital Research Alliance 2023). Similarly, ORCIDs make it easier to track the scholarly output of individual researchers.

The ability to permanently and uniquely reference arbitrary data subsets and subsequent versions of a dataset is key to safeguarding the reproducibility of scientific studies that rely on shared data. To tackle the technical challenge involved, groups such as DataCite (DataCite Metadata Working Group 2021) and the Research Data Alliance’s (RDA) Data Versioning Working Group (Klump et al. 2021; Klump et al. 2020) have developed approaches and recommendations to implement dataset versioning and dynamic data citation. In 2015 the latter group released an RDA recommendation describing the dynamic assignment of PIDs to every new, unique data query that produced a given data subset (Rauber et al. 2015). With this approach, when a dataset changes due to updates or reprocessing (Klump et al. 2021), or when a subset of data is extracted from a larger dataset, or republished within a larger data collection (as described in Klump, Huber & Diepenbroek 2016), these unique products can themselves be reconstructed identified, referenced, cited and reused. These RDA recommendations have been implemented in various data repositories that enable citation of time-stamped versions of subsetted dynamic datasets with persistent identifiers, facilitating retrieval, across sundry data types, for reuse (Rauber et al. 2021).

Of our present set of use cases, only the WDC-RRE repository reported having already implemented a system to assign PIDs to versioned datasets (WDC-RRE 2016), in which identifiers are coded to refer back to data queries executed on specific, timestamped dataset versions. Two others, INTERMAGNET and ISGI, expressed an interest in developing a PID versioning system in future stages of their repositories’ development. This approach would expedite the release of non-definitive datasets of geomagnetic observations, making these very detailed and highly valuable data assets available sooner to the scientific community. Another recent and well-documented example of metadata versioning from a WDS Member repository is Project MINTED at Ocean Networks Canada (Jenkyns & Ridsdale 2020; Jenkyns 2019), who also had an active role in developing the RDA’s Data Versioning WG’s outputs.

4.3.3. Maximizing data asset potential: Two approaches

To determine how much an existing repository infrastructure can achieve, and to pursue new development opportunities accordingly, an ongoing and thorough assessment of a repository’s infrastructure is recommended. To support a repository’s initial self-assessment, the global RDM community has produced instruments to assess the maturity and trustworthiness of a data repository and the data assets, including metadata records, it contains (Downs 2021; Peng 2018). Some practical, up-to-date frameworks for reviewing a repository’s current state are the most recent version of the CoreTrustSeal requirements for trustworthy data repositories (CoreTrustSeal 2022), the RDAs new FAIR data maturity model (FAIR Data Maturity Model WG 2020), the CARE Principles for Indigenous Data Governance (Carroll et al. 2020), and the TRUST Principles for digital repositories (Lin et al. 2020). Data repositories also need to continually assess the technology landscape to identify opportunities for improving capabilities to serve their designated communities. Cooperating with other repositories, within and across disciplines, helps with such assessments, especially when cooperating repositories share adoption stories and lessons-learned.

Two cases in our study reflect an interplay between changing user needs, evolving technologies, and resource constraints. The two geomagnetism data repositories, INTERMAGNET and ISGI, contain data assets with enormous potential for innovative, interdisciplinary research, but whose metadata formats and services have not been updated to current standards. For each repository, the challenge lies in finding a strategy that will allow them to exploit their data’s potential to serve their current (known) users as well as future (known and unknown) ones. It involves optimizing between general and use-case based repository developments, including metadata standards and exchange protocols. ISGI and INTERMAGNET have reported different strategies, based on different priorities, to respond to this challenge. INTERMAGNET has reported having to ponder the advantages of general-purpose, extensive standards that can open future (yet unknown) avenues of research and collaboration, versus use-case based approaches that tailor new developments to better support each new case. In contrast, the existence of concrete opportunities for interdisciplinary collaboration for example, between ISGI and researchers in the biological sciences may justify an approach that tailors a repository’s developments to a set of concrete use cases, taking a chance on their potential for future extensibility. HMetS-WG repositories also recognize the tension between the two fundamental principles of investing in future-proof technologies or maximizing user engagement with the data over time. In practice, repositories will usually attempt to balance both principles when designing their development plans.