In the academic environment, where educational, professional, and scientific content form the foundation of higher education and research institutions, unrestricted, free and open access (OA) to these resources is both essential and necessary. To enhance scientific communication and address the challenges of open science, the establishment of repositories has been strongly encouraged. Institutional repositories, as part of the open science infrastructure, serve as platforms for storing publications, research data, and other outputs of scientific research, as well as the overall work of higher education and research institutions.

Repositories are considered a core component of the green OA model, providing researchers an essential platform to archive and disseminate their scientific and scholarly outputs independently of traditional publishing channels. Most global strategic documents related to OA highlight repositories as a key element in achieving openness in science.

The Budapest Open Access Initiative (BOAI), launched in 2002, was the first major global initiative advocating for unrestricted and free online access to scientific information, particularly scholarly articles. This groundbreaking movement emphasized two primary approaches for achieving OA. The first, known as the gold route, involves publishing research directly in OA journals. The second approach – the green route, recommends self-archiving, whereby researchers deposit and publicly share their work through digital archives or repositories (Budapest Open Access Initiative [BOAI], 2017).

Based on the BOAI, many other initiatives with similar goals and aspirations have emerged. As early as 2003, the Bethesda Statement on Open Access Publishing and the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities were adopted. Both documents reinforced and expanded the principles outlined in the BOAI, highlighting the critical role of repositories. According to these statements, repositories should be maintained and supported by academic institutions, scientific associations, government agencies, or other established organizations dedicated to advancing OA (Max Planck Society, 2003; Suber, 2003).

In addition to the declarations and strategic documents at the European, global, national, and institutional levels, numerous initiatives and international organizations actively support the development of repositories as a key mechanism for achieving OA.

The Confederation of Open Access Repositories (COAR) is an international association founded in 2009 specifically dedicated to connecting individual repositories and repository networks (such as aggregators) with the aim of strengthening their capacity, aligning policies and practices, and representing the repository community on a global scale. It currently has over 150 members worldwide (COAR, n.d). The Registry of Open Access Repositories (ROAR) is a registry that tracks open repositories worldwide and promotes their visibility. It is part of the EPrints.org network, hosted at the University of Southampton, United Kingdom (Registry of Open Access Repositories [ROAR], 2025). OpenDOAR is a global directory of OA repositories that tracks and promotes their visibility worldwide. It provides a comprehensive list of open repositories, offering valuable data and insights for researchers and institutions. OpenDOAR is managed by SHERPA, a service provided by the University of Nottingham and Lund University (OpenDOAR, 2017).

Plan S is an initiative that mandates all scholarly articles funded by public sources to be openly accessible. This includes the requirement to deposit publications in open repositories without embargo. cOAlition S, a group of research funders, supports this initiative and aims to accelerate the transition to OA by ensuring that publicly funded research is freely available to all (cOAlition S, 2018). The Open Access Infrastructure for Research in Europe (OpenAIRE), in its strategic priorities (2023), emphasizes the necessity of modernizing repositories and other publication infrastructures to meet the evolving expectations of researchers.

While repositories have played a significant role in promoting open science, challenges remain, particularly regarding the extent to which research outputs are made openly available.

This paper examines the development and role of Croatia’s national repository infrastructure, assessing whether it has successfully fulfilled the principles of open science, especially openess of scholarly work. Furthermore, it explores the reasons why a significant portion of research outputs in repositories remains restricted or closed. By addressing these questions, this research provides a case study that may serve as a reference for other national repository infrastructures while contributing to broader discussions on open science policies, repository management, and potential reforms to enhance the accessibility and impact of scientific knowledge in Croatia, as well as at the European and international level.

Although certain institutional repositories in Croatia had existed for many years due to the initiative and enthusiasm of individuals, as well as the support of their higher education and research institutions, the national infrastructure was established in 2015.

Digital Academic Archives and Repositories (DABAR) is the national infrastructure for digital repositories in Croatia. It was developed by the University Computing Centre (SRCE) in collaboration with the National and University Library in Zagreb (NSK) and other higher education and research institutions (Ruđer Bošković Institute, Faculty of Humanities and Social Sciences and School of Medicine, both from University of Zagreb, and others). There are also the following working groups (WGs) composed of members from various higher education and research institutions in Croatia: WG for Master’s Theses,² WG for the Description of Scientific Papers, Controlled Vocabularies, and Identifiers, WG for the Description of Image, Audio, and Video Materials, Controlled Vocabularies, and Identifiers, WG for Interoperability, WG for Repository Policies Related to the Long-Term Preservation of Digital Materials, WG for User Functionalities, WG for Copyright, WG for Education and Support, WG for Data Sets, and WG for Educational Content (Digital Academic Archives and Repositories, 2021b).

Additionally, there is a Coordinating Committee, responsible for discussing and proposing development goals, tasks, and activities related to the development and maintenance of the DABAR system, including their content, scope, and expected implementation deadlines; proposing activities and work plans, including annual development plans for the DABAR system; and actively taking measures to ensure that plans are achieved and deadlines are met (Digital Academic Archives and Repositories, 2021a).

The DABAR infrastructure was primarily developed in response to a legal obligation. Since July 2013, the Republic of Croatia has enforced the Act on Amendments to the Act on Scientific Activity and Higher Education, which mandates that higher education institutions must permanently publish and store theses and dissertations in a publicly accessible online database of their home institution and NSK. DABAR enables higher education and research institutions, and libraries to store, manage, and disseminate all research outputs of an institution, such as theses and dissertations, scientific articles, proceedings, research data, and other scholarly materials. Aligned with international open science standards, it enhances the accessibility and visibility of academic and scientific work in Croatia while ensuring data interoperability and exchange.

Within the DABAR infrastructure, a system for tracking access statistics for all types of objects has been implemented. Additionally, national repositories monitor access through Google Analytics (Holub & Jertec, 2018). Great care is taken to enhance the visibility and promotion of repositories and their objects not only at the local but also at the international level, by participating in relevant global initiatives and services such as OpenDOAR, OpenAIRE, Research Data Alliance Europe (RDA), and the Catalogue of Data Repositories Re3data. Additionally, DABAR recommends the application of FAIR principles (Findable, Accessible, Interoperable, Reusable).

Two key national repositories are established – the Croatian Digital Theses Repository (ZIR) and the Croatian Digital Dissertations Repository (DR). ZIR was established at NSK in collaboration with SRCE in the summer of 2015. It ensures the permanent storage and public accessibility of undergraduate and graduate theses defended at higher education institutions across Croatia, enhancing their visibility and availability. Later that year, DR was launched to provide long-term preservation and OA to dissertations and scientific master’s theses. By aggregating content from all institutional repositories, DR serves as a centralized system for accessing advanced research outputs, supporting the dissemination and discoverability of scientific work in Croatia.

Currently, there are 182 repositories registered in DABAR, six aggregated repositories, including the two previously mentioned national repositories and four university repositories, and 176 institutional repositories (owned by public and private higher education institutions and departments, various institutes, libraries etc.). Most of these repositories are actively maintained, while some have only recently been established or have remained inactive for a certain period – either due to irregular deposition of objects or because they contain only a few (test) objects. Most repository administrators are also library staff from the institution. In the DABAR system, the storage process follows a bottom-up approach: objects are first deposited in institutional repositories, then aggregated in university repositories if the institution is part of a university, and finally, in the national repository in the case of theses and dissertations. This variability in activity highlights the dynamic nature of repositories and the differing levels of engagement across institutions.

Since 2021, DABAR implemented the central search so users can search all digital objects stored in any repository in DABAR in one place and download object files from the original repository.

Changes in the legislative framework could significantly impact the practice of publishing theses and dissertations in Croatia. According to the Act on Scientific Activity and Higher Education (Narodne novine, 2022), higher education institutions are required to publish theses and dissertations in the national repository or their own institutional repository. Furthermore, the WIPO (2021) explicitly states that a student cannot object to making their final thesis, created during any study at a higher education institution, publicly available in the online database of the higher education institution’s library and/or the public online database of final theses at NSK. Unfortunately, there is still no mandatory requirement for the deposit of other scientific outputs of Croatian higher education and research institutions in OA on national level.

Institutional repositories emerged in the mid-1990s as essential components of scholarly communication infrastructure. Lynch (2003) emphasized their transformative potential for higher education institutions and scientific communities, identifying them as key tools for achieving various academic and societal goals.

Asadi et al. (2019), through a systematic review of literature from 2007 to 2018, observed that most of the research studies were concentrated on deployment and implementation challenges, with limited awareness of OA and inadequate technological infrastructure repeatedly cited as barriers. Despite extensive studies on repository growth, a clear understanding of how institutional characteristics shape access status remains incomplete.

Further reinforcing the need for a holistic approach, Schöpfel and Prost (2013) observed that while institutional repositories offer new opportunities for disseminating scientific information, their effectiveness is often hampered by inconsistent content policies, low levels of researcher participation, technical challenges, and variability in the quality of deposited materials. Their study underlines that successful repository development requires not only technological solutions but also strategic institutional engagement and content standardization.

Existing studies suggest that repository access policies are strongly influenced by institutional profiles – type of institution and scientific discipline. Taubert et al. (2024) demonstrated that in Germany, the disciplinary orientation of universities, whether predominantly STEM or SSH, was a major determinant of OA repository uptake. Recent findings by Hadad and Aharony (2023) further emphasized disciplinary differences in self-archiving practices, showing that STEM researchers predominantly deposit pre-/post-print versions in subject-based repositories due to disciplinary norms and funding mandates, while SSH researchers tend to share links to published articles via academic social networks, often without full awareness of copyright restrictions.

Similarly, Baro and Nwabueze-Echedom (2022) highlighted that in English-speaking African universities, repositories were primarily shaped by available resources, institutional policies, and technical capabilities, with a focus on theses and dissertations. While these findings provide valuable insights into the importance of disciplinary and resource-based factors, less is known about how national repository infrastructures, like Croatia’s DABAR system, mediate these institutional differences. Gudelj et al. (2022) found significant variations in the accessibility of master’s theses among SEA-EU Alliance universities, revealing that even within structured alliances, mandatory deposit policies were inconsistently applied. This suggests that national or alliance-level frameworks do not uniformly guarantee OA, raising questions about the effectiveness of broader repository mandates.

In Croatia, Holub and Jertec (2018) documented how the DABAR infrastructure provides automated workflows and interoperability, theoretically simplifying deposit and increasing OA potential. However, Čadovska and Milovanović (2019) revealed that many Croatian higher education institutions lacked the necessary documentation to support public deposit, indicating that institutional readiness was insufficient despite national infrastructure being in place. This highlights that while repository systems can enable OA, institutional characteristics such as policy completeness and administrative support critically determine actual access status. The findings should be interpreted with caution, as significant time has passed since the original research was conducted and its findings may no longer fully reflect the current institutional landscape.

The relationship between self-archiving options, institutional policies, and OA transitions has been a focal point of multiple studies. Recent comparative research by Roy et al. (2023) offers further insight into the challenges surrounding institutional OA self-archiving policies. Their analysis of 66 repositories listed in OpenDOAR, ROAR, and ROARMAP revealed significant deficiencies in key policy areas, including copyright and licensing, embargo management, access policies, and multilingual user interface development. The study found that most institutional repositories failed to clearly define copyright ownership, did not specify re-use licenses, and often tolerated embargo periods that undermined the principles of immediate OA. Moreover, policies concerning non-textual content and non-English resources were largely absent. Based on these findings, the authors advocate for the adoption of institute-specific policy frameworks aligned with best practice recommendations, emphasizing the necessity of comprehensive rights management, minimized embargo periods, and active promotion of repository use through clear self-archiving mandates. Their conclusions further underline the idea that technical infrastructure alone is insufficient; well-developed, transparent, and supportive institutional policies are essential for achieving true OA.

Further, the effectiveness of institutional policies in promoting self-archiving appears uneven. Asadi et al. (2019) highlighted that without strong institutional commitment and user education, self-archiving remains underutilized. These findings collectively suggest that even where technical solutions are in place, institutional policies must be clear, enforceable, and accompanied by education and support mechanisms to foster genuine open access transitions.

Building on the importance of infrastructure and content management, Zhou et al. (2025) demonstrated that the quality of information, robust technological infrastructure, and repository usability are key factors shaping positive user perceptions of OA repositories. Their findings emphasize that beyond technical availability, ensuring high content quality and intuitive platform design are critical for fostering trust, satisfaction, and willingness to use OA repositories in academic research. However, as Turk et al. (2024) noted, despite robust repository development, the adoption of OA for certain object types remains limited, suggesting that technical capabilities alone are insufficient without supportive institutional incentives or mandates.

A significant body of research has also explored why repositories maintain closed or restricted access despite OA policies. Tmava (2022) found that faculty perceptions (including fears of plagiarism, concerns over copyright, unfamiliarity with repository goals, and doubts about repository prestige) act as strong deterrents to open participation. Baro and Nwabueze-Echedom (2022) similarly pointed to copyright restrictions and the absence of repository policies as major barriers in African universities, suggesting that legal and perceptual obstacles are not confined to resource-limited contexts but are structural issues across different regions. Similar findings were reported by Kakai (2021), who demonstrated that low open access levels in university repositories in Kenya, Tanzania, and Uganda were primarily caused by the absence of institutional policies, reliance on mediated rather than self-archiving practices, and limited researcher engagement, despite general support for OA principles.

Milovanović and Matijević (2023) demonstrated that at the University of Zagreb, objects with restricted access often had higher view-to-download ratios than openly available ones, challenging assumptions that OA automatically increases usage. This finding indicates that repository visibility and accessibility involve complex user behaviour, further complicated by access restrictions. Stubičan Ladešić et al. (2022) provided additional evidence of societal demand for OA by documenting high user interest in unavailable theses, particularly among non-academic users. This highlights a broader public need for accessible academic content, underscoring the societal cost of maintaining restricted access.

While substantial progress has been made in understanding repository development, adoption patterns, and barriers to OA, critical gaps remain regarding the influence of institutional characteristics, the real-world effects of self-archiving policies, and the complex motivations behind maintaining closed or restricted access. These insights formed the basis for the development of the research questions and methodological approach that will be presented in the following sections.

The research was conducted in the first half of 2024, with quantitative data collected until May 27, 2024, from official DABAR system analytics – https://dabar.srce.hr/reports/. All data processing, calculations, and visualizations were performed using Microsoft Excel within the Microsoft 365 business cloud environment. At that time, the DABAR system contained 262,073 digital objects, including theses and dissertations, journal articles, conference papers and presentations, books and book chapters, research data, data management plans (DMPs), educational resources, audio, video, images, and virtual collections.³

There are five types of access defined for stored objects in the DABAR system – Open Access (OA), Embargo, Restricted Access, Institutional Access, and Closed Access. Regardless of access type, the metadata is publicly available from the moment of deposit. OA allows unrestricted public availability of the full text. Embargo means that the full text remains inaccessible until a predetermined period expires. After a maximum of two years, all objects under Embargo are automatically made available in OA. Restricted Access provides full-text access only to users within the Croatian higher education and research system, and Institutional Access limits full-text availability to staff and students of the institution that deposited the work. Closed Access means that the full text is entirely inaccessible to users. Of all the objects, only 51% were in OA at the time of the study, indicating a significant proportion of objects with restricted access.

The distribution of OA objects among various research areas reveals notable differences in accessibility (Figure 1). Social Sciences lead in the absolute number of published objects (96,972), with 37.82% available in OA. Engineering and Technology follow, with 59,889 published objects and a slightly higher OA percentage of 44.21%. Medical and Health Sciences demonstrate a significant commitment to OA, with 66.44% (26,168 out of 39,381) of publications freely accessible. Humanities and Natural Sciences show the highest OA percentages, at 74.25% and 79%, respectively. In Biotechnology, 65.93% of publications are OA. Arts and Interdisciplinary Sciences exhibit lower overall publication volumes, with OA percentages of 44.16% and 52.12%, respectively. These results suggest that while the volume of published objects varies significantly by field, disciplines such as Humanities, Natural Sciences, and Medical Sciences show a stronger inclination toward OA dissemination.

An analysis of access types for published objects in the DABAR system reveals significant variations depending on the type of object (Figure 2). Among the most accessible categories, journal articles have the highest proportion of OA – 91.8% (18,324 out of 19,965). Similarly, conference papers (93.3%) and book proceedings (90.5%) demonstrate a strong commitment to OA. Theses and dissertations also exhibit a high level of accessibility, with 65.5% (6,162 out of 9,403) in OA. Educational content (84.1%), datasets (78.7%), and books (72.4%) also show relatively high OA availability.

However, certain categories remain predominantly restricted. Artistic theses and final papers have a significantly low OA rate, with only 11.4% (33 out of 289) available. Similarly, book chapters (47.8%), images (44.8%), and audiovisual materials (8.7%) have lower OA representation. The largest category, undergraduate, graduate, and specialist theses, includes 222,857 deposited works, of which 103,087 (46.3%) are in OA.

Institutional repositories represent an essential role in promoting transparency, visibility, and accessibility of scholarly outputs. Thay are one of the most important pillars of OA and open science movement. This study of institutional repositories within Croatia’s DABAR system provides brief research of the factors contributing to large percentage of closed or restricted access, despite institutional and policy-level support for openness.

While most repositories are situated within public higher education institutions and cover a wide range of scientific disciplines, access limitations persist due to a combination of structural, procedural, and cultural factors. Legacy policies, selective self-archiving permissions, particularly for theses and dissertations, and concerns over confidentiality, copyright and content quality contribute to a fragmented and cautious approach to repository openness. The uneven implementation of OA practices suggests that technical infrastructure alone is insufficient.

Addressing these challenges requires a multifaceted approach involving the updating of outdated institutional policies, the establishment of clear self-archiving procedures, and active engagement with researchers to foster trust in OA practices. Improvements in repository openness are not only essential for fulfilling the goals of open science but are also critical for maximizing the impact and visibility of national and institutional research outputs.