Digital libraries, so-called, first emerged in the early- to mid-1990s, paralleling the emergence and explosive growth of the World Wide Web. Digital library research and development was given initial impetus by some major projects: in Europe by the EU Libraries Programme, in the USA by the Digital Library Initiatives of the National Science Foundation, and in Britain by the eLib range of projects initiated by JISC. The early digital libraries were in the nature of isolated research projects, peripheral within the overall information landscape. At the present day we see digital libraries occupying a more central and integrative role, and the last few years have seen enormous growth, with new horizons opened up over a broad range of issues. The field is enormous; this paper can provide only a very brief overview and some pointers to recent work in key areas of digital library research and development.
Views about trends in the development of digital libraries, and a fortiori concerning the future of libraries in general, are very much influenced by different understandings and definitions of the term "digital library". It may be used in a reductive sense to denote a technical infrastructure supporting a collection of documents (Seadle and Greifeneder, 2007). Experiences of web searching often influence people’s expectations of digital libraries, sometimes unconsciously (Bawden and Vilar, 2006). The problems and issues for digital library research are then perceived primarily in terms of search and access. However, as Lagoze (2005) remarks, "These functions are essential (and remain challenging) but they are just part of an information environment. Traditional libraries are much more than well-organized warehouses of books, maps, serials etc. In their full expression, they are places where people meet to access, share and exchange knowledge".
Perhaps the most comprehensive and useful definition is that of the Digital Library Federation (2002): digital libraries are:
" ... organizations that provide the resources, including the specialized staff, to select, structure, offer intellectual access to, interpret, distribute, preserve the integrity of, and ensure the persistence over time of collections of digital works so that they are readily available for use by a defined community or set of communities".
Such a definition includes the three key components of the theoretical frameworks underpinning digital libraries, namely
- information resources, and
Also it emphasizes the aspects of service to and use by a community of users that are characteristic of traditional libraries.
In this survey of recent work in the digital library field I have used Shiri’s categorization (Shiri, 2003) of issues in digital library research and development. I have based it predominantly on work published in Emerald journals within the last two years, mostly reviews and conceptual papers, but including also some more technical case studies. Under some of these headings there is little suitable literature available anywhere, and I have summarized them only briefly. Shiri’s classification is as follows:
- architecture, systems, tools and technologies
- digital content and collections
- knowledge organization systems
- users and usability
- legal, organizational, economic and social issues.
Architecture, systems, tools and technologies
This category covers all technical, infrastructural and system-related aspects of digital libraries, including network architectures, search and retrieval techniques, and user interfaces.
Digital content and collections
This category includes issues of collection development, digital publishing, and digital preservation; the latter, as described by Joint (2006a) presents acute problems related to the relative impermanence of digital information formats. The challenges here cover emulation, migration, continual synchronization, backup, and security (Baker, 2006; Fox, 2006a). There appears to be little recent literature devoted specifically to digital collection management, although Nikolaidou et al. (2005) provide an interesting case study of managing multiple collections in a medical digital library.
Schemes and standards for metadata (literally "data about data") are fundamental to libraries of all kinds. Metadata is commonly categorized as descriptive (or intellectual), structural and administrative. Descriptive metadata describes the digital object itself, and corresponds to the library catalogue record of a printed resource. Structural metadata describes how an item is structured and organized, and administrative metadata describes such things as how the object was produced, its ownership, and who has accessed it. Dublin Core has been devised as a simple, flexible metadata standard for digital objects (Hillman, 2004). The digital environment presents particular challenges, particularly in relation to the diversity of formats and how digital objects may be related within a particular information context. With ever-increasing number of digital objects to be managed, there are also problems of metadata generation, maintenance and quality control, which can affect the scalability of digital library systems (Beall, 2004; Yousefi and Yousefi, 2007).
Interoperability, i.e. the ability of digital libraries with different architectures and metadata formats to interact effectively through the application of a range of protocols and standards, is one of the most intensive areas of digital library research.
What is known as deep semantic interoperability, the ability to access, consistently and coherently, similar classes of digital objects and services across distributed information resources, with mediating software or "middleware" compensating for local variations, has been described as the "holy grail" or "grand challenge" of digital library research (Lynch, 1995).
The Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) is the most widely discussed and investigated standard for digital repository interoperability (Suleman et al., 2003). SRU/SRW is a promising successor to Z39.50 as a federated search protocol. The Resource Description Framework (RDF) provides a metadata framework for representing relationships between digital objects, and is a forerunner in efforts to implement Berners-Lee’s vision of a "semantic web" (Berners-Lee et al., 2001; Fox 2006b; Robu et al. 2006).
A themed issue of Library Management (Vol. 26 Nos. 4/5, 2005) was devoted to semantic web technologies and digital libraries. Here Sure and Studer (2005) give an informative overview of recent semantic web technologies which can be used to enhance digital libraries, while Warren and Alsmeyer (2005) offer a case study of a digital library project employing semantic technology.
Related to metadata and interoperability is a range of standards relating to collection development, preservation, electronic publishing, metadata, persistent identification of digital objects, and user authentication in digital libraries. The Handle system, and the Digital Object Identifier (DOI) system which is an implementation of it, have been developed for object naming.
Ball and Plott (2004) and Chandrakar (2006) provide overviews of the DOI system, which is defined as "a character string used to identify intellectual property in the digital environment. It provides a framework for linking users with content owners, facilitating electronic commerce, and enabling automatic copyright management".
Systems such as ATHENS (a centralized service provided by Eduserv, a not-for-profit organization) and Shibboleth (a devolved standards-based open source system which can be managed within a consortium of institutions) are employed for user identification and authentication. Hudomalj and Jauk (2006) provide an informative overview of the authentication and authorization services used by academic libraries in Europe.
Knowledge organization systems
These include the thesauri, taxonomies and classification schemes which are used to index documents and provide navigation structures within an information space.
Users and usability
Studies of the usability and impact of digital libraries – how users interact with the information resources within them, and how they support research, teaching and practice within their parent institutions – have been extended to the digital sphere. A major problem for the users of digital libraries can be deciding where to look for a specific item of information, and also consolidating the results retrieved from heterogeneous systems.
The use of personalization services or web aggregators to gather, filter and present information relevant to the user has been suggested as possible solutions. This work has been comprehensively reviewed by Chowdhury et al. (2006) One particularly active area of research is the convergence of virtual learning environments (VLEs) and digital libraries (e.g. the INSPIRAL project: Currier et al., 2001; Secker, 2004); general issues in this area are reviewed by Sharifabadi (2006).
Legal, organizational, economic and social issues
These include rights management, intellectual property and copyright, new business models, social perceptions of digital libraries, and the effect of digital library technologies on the role of librarians and library services in general.
The use of digital rights management technologies, for instance, creates difficulties for libraries in supporting fair use or access from multiple locations. In a digital environment in which libraries own less and less of the information they support and distribute, rights management issues assume considerable prominence (Davis and Lafferty, 2002). Libraries which manage digital repositories holding substantial research outputs, e.g. of eScience data, are increasingly themselves custodians of intellectual property (Hey and Hey, 2006).
Several substantial thematic analyses of digital library history, themes and trends and of the impact of digital libraries on academic library services have appeared recently, e.g. Baker (2006), Collier (2006), Dempsey (2006), Lynch (2005). Common to several of these is the suggestion that within the digital environment academic libraries are becoming more deeply engaged in the creation and dissemination of knowledge, rather than simply acting as custodians, and are becoming essential collaborators in these activities.
In this environment, librarians have become key facilitators of information literacy. Dempsey (2006) discusses the "flattening" of the information environment (with possibilities for co-creation of digital content) which has been facilitated by technologies such as web services and RSS, and the need to project library services into the user’s workspace.
Among the analysts and forecasters of digital library futures, Joint (2006b) is perhaps the most radical. He suggests that contemporary digital library change represents not simply a change in technological processes, but a fundamental cultural shift. According to this theory, the present-day digital library is an interim phenomenon, based on an outdated metaphor derived from traditional print libraries. In a postmodern information world, however, bibliographic description, collection management and digital preservation are inherently impossible; anarchic storage and distribution of electronic content will become the norm.
During the last ten years digital libraries have moved from the periphery to the mainstream within academic, professional and public sector environments. This paper has presented a brief and highly selective overview of recent developments and trends in digital libraries, including both technical and cultural aspects.
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