The advent of information and communication technology (ICT) has revolutionized the way information is generated and disseminated in modern times. As a result, many organizations have moved from paper-based systems to become more digital-oriented organizations. This wave of change has also been observed within libraries. According to the British Library Digitization Strategy Plan 2008- 2011 (2008), “the advent of the Internet and the ability to digitize large quantities of text and images and make them available over the Web has transformed ways of working” (p. 1). The need to harness the numerous benefits of this modern technology has given rise to various digital library (DL) initiatives across the globe. Libraries, especially academic libraries, are now investing heavily on electronic library services with a view to providing seamless access to library collections. The traditional methods of collecting, storing, processing, and accessing information have undergone a massive transformation due to the growth of virtual libraries, digital libraries, online databases, and library and information networks (Varatharajan & Chandrashekara, 2007). Information users in the present digital era can access the vast digital collection of libraries by using computers connected to the Internet to search and retrieve needed information from electronic catalogues, e-journals, and large databases of digitized scholarly information (Marcum & George, 2003).
This new trend in library practice has generated a great deal of challenges in the areas of design, application, acceptance, and the use of technology by potential library users. Another major challenge to libraries in the digital era is the difficulty surrounding DL
2. THE CONCEPT OF THE DIGITAL LIBRARY
The digital library is not a new concept in librarianship. However, its evolution in the modern era has opened up a new chapter in the history of information generation, processing, preservation, and dissemination. The goal of the DL is to facilitate easy and remote access to library collections. Roknuzzam et al. (2009), quoting Gapen (1993), defined the DL as “the concept of remote access to the contents and services of libraries and other information resources, combining an on-site collection of current and heavily used materials in both print and electronic form, with an electronic network which provides access to, and delivery from, external worldwide library and commercial information and knowledge sources” (p. 374). According to Mutula and Ojedokun (2008) an ideal DL should be able to provide users with access to electronic information resources via electronic means. This is reflected in a recent definition of DL by IFLA (2010) as a “collection of digital objects, of assured quality, that are created or collected and managed according to internationally accepted principles for collection development and made accessible in a coherent and sustainable manner, supported by services necessary to allow users to retrieve and exploit the resources” (p. 2).
This development in library practice had been predicted by Vannever Bush, who envisioned a device which he called the ‘memex,’ a mechanized system based on microfilm technology which would be able to store large amount of books, records, and communication, with the ability to be consulted and retrieved with exceeding speed and flexibility (Bush, 1945). This prediction was further made clearer by Licklider (1965) in his book titled
3. COMPONENTS OF DIGITAL LIBRARIES
DLs are comprised of various components that interact together to serve information needs of end users. The literature shows that digital libraries, like traditional libraries, share common functional components such as content, digital object, metadata, repository, identifier, Internet and Intranet, digitization, and user interface (Arms, 1995; Magnussen, 2003; Pandey, 2003; Altman, 2006; Bhuyan, 2007). These components can be grouped into five core element which include content, organization, service, technology, and people (Carter, 2002). Each of these five elements is discussed in the paragraphs that follow:
DLs are still developing and most of the components identified by various researchers in the field of digital libraries focus on the above five core elements of digital libraries. The goal of any information institution is to meet the information needs of its parent body or community. Therefore, digital objects must be properly selected based on the needs of potential users and organized for easy accessibility. DL architecture provides good user interfaces that enable users to navigate the vast numbers of digital objects in the library repositories with ease.
4. CHARACTERISTIC OF DIGITAL LIBRARIES
DLs have unique characteristics. Their unique characteristics have been discussed in various conferences and fora in many parts of the world, such as: European Conference on Research and Advanced Technology for Digital Libraries (ECDL); International Conference on Asia-Pacific Digital Libraries (ICADL); and International Conference on Theory and Practice of Digital Libraries (TPDL), just to mention few. Several researchers have equally examined the various characteristics of digital libraries against the features of traditional libraries (Cleveland, 1998; Chowdhury, 2003). These characteristics show the flexibility, portability, and accessibility of DLs over traditional libraries.
DLs generally share the following common characteristics:
They provide round the clock services to users within and without the library environment. Users can access digital objects at any time 24/7.
They provide a coherent view of all information contained within a library, no matter its form or format (e.g. text, audio, and video).
Contents in digital libraries can only be accessed through the help of computers.
Several users can access a digital object at the same time in different locations.
Digital libraries do not require large spaces, unlike traditional libraries where physical space is needed for building and maintaining collections.
These characteristics show a shift from traditional library practice, where users need to physically visit library buildings to have access to collection. The dynamics of services in digital libraries has over the years attracted several models and theories of DLs proposed to serve as a framework for building digital libraries that will meet the information needs of users in the new global environment. As pointed out by Goncalves et al. (2004), formal models and theories are crucial in order to specify and understand clearly and unambiguously the characteristics, structure, and behavior of complex information systems. In line with this assertion, different practical and research efforts towards models and theories of digital libraries have been developed. The Digital Library Initiative (DLI) projects in the USA and the eLib projects in UK have been the major drivers of these efforts through research and practical projects. There are now a number of models of digital libraries that can serve as a framework for best practices.
5. MODELS AND THEORIES OF DIGITAL LIBRARIES
The terms
The DL is one of the byproducts of the evolution of digital technologies in the late twentieth century. In effect, it has witnessed a great deal of development in the areas of design, application, and use. Most of the institutions and agencies that have embraced DLs have adopted various approaches. Some have employed a system-oriented approach while some embraced usercentered approaches. These developments have driven the need for common foundations that foster best practices to shape development in the field of DLs (Candela et al. 2011). Over the years, various models and theories have been developed with the aim of addressing issues generated from the development of DLs. Examples of such efforts include the DELOS Digital Library Reference Model, the International Committee for Documentation of the International Council of Museums (CIDOC), the Conceptual Reference Model, the Cornell Reference Architecture for Distributed Digital Libraries (CARDDL), and the 5S Theory.
These models of DLs are some of the on-going efforts in the DL universe towards providing a framework for standards and best practices. The DELOS Reference Model and 5S Theory are general attempts toward a conceptual framework, while the CARDDL and CIDOC Conceptual Reference Models focus on specific domains of digital libraries. The DELOS Reference Model and 5S Theory, apart from being general models, are also the two prominent models of digital libraries (Goncalves et al. 2004; Candela et al. 2007; Shen et al. 2008; Murthy et al. 2010). They are therefore analyzed for better understanding of their application in the digital library universe.
6. THE DELOS DIGITAL LIBRARIES REFERENCE MODEL
The DELOS Digital Library Reference Model is a conceptual framework aimed at addressing major entities and their relationships in the digital library universe. The DELOS DL reference model is one of the results of the DELOS Network of Excellence, a DL project partially funded by the European Commission. The DELOS project aims at integrating and coordinating the ongoing research activities of the major European teams working in DL-related areas with the goal of developing the next generation DL technologies. Among the objectives of the project are to:(i) define unifying and comprehensive theories and frameworks over the life-cycle of DL information; and (ii) build interoperable multimodal/multilingual services and integrated content management ranging from the personal to the global for the specialist and general population (Casarosa, 2007). In achieving these objectives, the DELOS Reference Model was designed as a framework for the development of appropriate systems. The model is built on six main domains: content, user, functionality, quality, policy, and architecture. These are briefly discussed:
(1)
The DELOS Reference Model is a product of brainstorming workshops of stakeholders in the digital libraries field. This led to the drafting of the Digital Library Manifesto with the aim of identifying the cornerstone concepts within the DLs community. The manifesto introduced a three tier framework:
Digital Library Management System (DLMS)
Digital Library System (DLS)
Digital Library (DL)
The interconnectivity of these three systems and the six main domains of the reference model is graphically shown in Figure 1.
The first tier, Digital Library Management System (DLMS), is a generic piece of software providing basic functionality required by the particular DL. The second tier, Digital Library System (DLS), is built on top of DLMS and enriches it with specific functionality and/or configurations required by the digital library. Finally, the third tier, Digital Library (DL), is understood as an organization collecting and preserving digital content and giving access to it (Murthy et al. 2010). This three-tier framework interacts with the six domains of the DELOS Reference Model (content, user, functionality, quality, policy, and architecture) to provide allembracing DL services. The players in the DL universe include End users, Designers, System Administrators, and Application Developers. These individuals play a significant role in DL design and application.
For almost a decade after its emergence, the DELOS Reference Model has made significant strides in defining the essential DL concepts and relationships (Candela et al. 2007). It has provided a common vocabulary to facilitate communication between researchers, users, and designers of digital libraries. It has also laid out the digital library concepts in a clear and structured way. However, the model was heavily revised with guidance and contributions from the international members of a range of DL working groups during the DL.org project (Candela et al. 2011). Apart from its comprehensive and explicit illustration of DLs domain, the model provides a conformance checklist that can serve as a benchmark or assessors to determine whether or not their library is compliant with the DELOS digital library reference model. The model has identified players in the DL universe which can equally serve as a guide to any library, organization, and individual intending to embark on a DL project. Evidently the application of the DELOS Reference Model will guide designers of DLs in how to address various components of digital libraries.
The 5S Theory is a product of efforts aimed at providing theoretical and practical unification of digital libraries. It provides a foundation for the definition of the digital library through the use of five (5) fundamental abstractions, namely Streams, Structures, Spaces, Scenarios, and Societies. The 5S Theory defines a “core” or a “minimal” DL, i.e., the minimal set of components that make a DL, without which a system/ application cannot be considered a DL (Murthy et al 2007, 2010). Its flexibility as an instrument for analyzing DL development and organization has been demonstrated in several respects (Shen et al. 2008; Murthy, et al. 2010). Table 1 shows how 5S constructs can be employed to describe key concepts of DLs such as digital objects, metadata, collections, and services.
The 5S Framework
These abstractions provide a formal foundation to define, relate, and unify concepts in the DLs. They are used to define other DL constructs such as digital objects, metadata specification, collection, repository, and services (Doerr et al. 2007). For example, a digital object may be defined in terms of its structured storage stream and structured metadata specification. The interplay of the 5S constructs and how each of the constructs leads to a minimal digital library system is illustrated in Figure 2.
The 5S framework describes minimal requirements for a DL and how the 5S constructs relate with the various components of DLs. For example, digital objects are composed of streams. These include: data; structured streams (tables of contents, chapters, etc.); and structural metadata specification (which describe each digital object for easy retrieval). Scenarios, according to Goncalves (2004), consist of “sequences of events or actions that modify the states of a computation in order to accomplish a functional requirement” (p. 2). The scenarios as shown in Figure 2 link the DL services and the societies it serves. The 5S framework focuses on defining the minimal set of features belonging to a digital library. The minimal DL is defined as a quadruple (Repository, Metadata Catalogue, Services, Society) containing the core digital library components. The applicability, versatility, and unifying power of the 5S model are demonstrated through its use in three distinct applications: building and interpretation of DL taxonomy, informal and formal analysis of case studies of digital libraries, and utilization as a formal basis for a DL description language (Goncalves et al. 2004).
8. COMPARISON OF DELOS REFERENCE MODEL AND 5S THEORY
The DELOS Reference Model is intended as a roadmap to enable the wider digital library community to follow the same route and share a common understanding when dealing with the entities of the DL universe (Innocenti et al. 2011). In addition, the 5S Theory is built on this premise to provide a foundation for the definition of the digital library toward achieving theoretical and practical unification. The two models/theories have common objectives. These objectives are to provide a standard framework for DL projects. However, the methods employed in the presentation of DL frameworks are quite different, though their concepts still address the core components of DLs. While 5S Theory applies a rigorous definition of various concepts to DLs, the DELOS model focuses on identifying the main concepts and relationships encompassing the entire digital library. This is opposed to the 5S definition of individual DL aspects in terms of abstract entities, and these five levels of abstraction and their associated formalisms also render it difficult to adopt due to the complexities involved (Phiri, n.d.). The DELOS Reference Model’s six (6) main domains: content, user, functionality, quality, policy, and architecture, are explicit and serve as a foundation for assessment of DLs. However, the organization of three distinct systems (Digital Library, Digital Library System, and Digital Library Management System) into one framework makes the DELOS model complex in nature. It also lacks strong emphasis on social aspects of digital libraries compared to 5S Theory (Fox et al 2003). There are some areas covered in the DELOS Reference Model’s six main domains which are not distinctly represented in the 5S main constructs. They include policy and quality domains. 5S Theory provides a separate quality model which makes up for quality constructs not explicitly covered in the main 5S constructs.
Apart from the above differences there are some common relationships shared by these models. These common relationships are in such areas as Streams, Contents, Societies, and Users constructs. These two related concepts address the same component of a DL. The commonality of the two concepts can be vividly identified when applied to different DLs such as institutional based DLs (e.g. a University Digital Library) and a collaborative DL (e.g. the Networked Digital Library of Theses and Dissertations (NDLTD). For example, a university DL will serve the information needs of members of the university community, referred to as
9. CONCLUSIONS AND FUTURE WORK
The proliferation of digital library initiatives with different patterns of application systems calls for a unified model that will shape the development of the DL universe. The DELOS Reference Model and 5S Theory are the two prominent attempts in that direction. They are developed to guide in the design of various digital library initiatives. The aim of this development is to guide DL designers towards building DLs that will meet the information needs of users in the new global environment. However, there is still a dearth of research on their application. Therefore there is a need to examine various digital library initiatives using either of these two models as a framework for better understanding of patterns of DL initiatives. The outcome of such research will help to validate the applicability and usefulness of such models.