Digital library interoperability at high level of abstraction

Highlights

• Foundational models for digital libraries.

• Interoperability among digital library systems and possible approaches.

• Unifying semantic model and ontology for high-level interoperability among digital library systems.

• In depth analysis of the user, content, functionality and quality domains in digital libraries.

• Concrete use case on annotation of illuminated manuscripts to illustrate how to apply the proposed methodology.

Abstract

Digital Library (DL) are the main conduits for accessing our cultural heritage and they have to address the requirements and needs of very diverse memory institutions, namely Libraries, Archives and Museums (LAM). Therefore, the interoperability among the Digital Library System (DLS) which manage the digital resources of these institutions is a key concern in the field.

DLS are rooted in two foundational models of what a digital library is and how it should work, namely the DELOS Reference Model and the Streams, Structures, Spaces, Scenarios, Societies (5S) model. Unfortunately these two models are not exploited enough to improve interoperability among systems.

To this end, we express these foundational models by means of ontologies which exploit the methods and technologies of Semantic Web and Linked Data. Moreover, we link the proposed ontologies for the foundational models to those currently used for publishing cultural heritage data in order to maximize interoperability.

We design an ontology which allows us to model and map the high level concepts of both the 5S model and the DELOS Reference Model. We provide detailed ontologies for all the domains of such models, namely the user, content, functionality, quality, policy and architectural component domains in order to make available a working tool for making DLS interoperate together at a high level of abstraction. Finally, we provide a concrete use case about digital annotation of illuminated manuscripts to show how to apply the proposed ontologies and illustrate the achieved interoperability between the 5S and DELOS Reference models.

Introduction

Digital Library (DL) have been steadily progressing since the early 1990s and they now determine how citizens and organizations study, learn, access and interact with their cultural heritage  [1], [2], [3], [4], [5], [6], [7], [8]. Despite their name, DL are not only the digital counter-part of traditional libraries but they are also concerned with other kinds of cultural heritage institutions, such as archives and museums, that is institutions typically referred to as Libraries, Archives and Museums (LAM). In the context of LAM, unifying a variety of organizational settings and providing more integrated access to their contents are aspects of utmost importance. Although the type of materials may differ and professional practices vary, LAM share an overlapping set of functions and fulfilling them in “collaboration rather than isolation creates a win–win for users and institutions”  [9].

These compelling integration and collaboration needs have propelled the evolution of Digital Library System (DLS)   [10] as systems that permit us to design and implement the overlapping set of functions of LAM.

In the 1990s, DLS were monolithic systems, each one built for a specific kind of information resource–e.g. text, images, or videos–and with very specialized functionalities developed ​ad hoc for those contents and their reference users. This approach caused a flourishing of systems where the very same functionalities, e.g. user management or repositories, were developed and re-developed from scratch many times, causing them to be different and often incompatible one with each other. From the mid 2000s, DLS evolved towards service-oriented architectures, where components can be plugged into each other to provide the desired end-user functionalities, yet requiring careful and ad hoc configuration. This paradigm shift allowed DLS to become more and more user-centered systems, where the original content management functionality was partnered with new communication and cooperation functionalities such as user annotation  [11], with the ultimate goal of acting as “a common vehicle by which everyone can access, discuss, evaluate and enhance information of all forms”  [12]. As a consequence, DLS started to embody the above vision for LAM since they were no longer isolated systems but, on the contrary, they needed to cooperate together in order to improve the user experience in accessing information and to seamlessly integrate information resources of different cultural heritage institutions.

This evolution has been favored by the development of two foundational models of what DL are, namely the Streams, Structures, Spaces, Scenarios, Societies (5S) model  [13] and the DELOS Reference Model   [14], which made it clear what kind of entities should be involved in a DL, what their functionalities should be and how DLS components should behave, and fostered the design and development of operational DLS complying with them.

However, these two models are quite abstract and, still providing a unifying vision of what a DL is, they allow for very different choices when it comes to develop actual DLS. This has led to the growth of “ecosystems” where services and components may be able, at best, to interoperate together within the boundaries of DLS that have been inspired by just one of the two models for DL. However, there are no running examples of two DLS, one implementing the 5S model and the other the DELOS Reference Model, which are able to interoperate. Therefore, interoperability still represents one of the biggest challenges in the DL field  [10], [15].

In this work, we address a still open issue in the DL realm: to make DL foundational models interoperable in order to derive all the other kinds of interoperability, in particular, interoperability between operational DLS. The main contributions of the paper are:

• a detailed analysis of the 5S and DELOS Reference models pointing out common aspects and main differences;

• the definition of a common ontology which encompasses and links the concepts of the DELOS Reference Model and the 5S models, covering all the domains of such models: the user, content, functionality, quality, policy and architectural component;

• a concrete use case about digital annotation of illuminated manuscripts to show how to apply the proposed ontologies and illustrate the achieved interoperability between the 5S and DELOS Reference models.

The paper is organized as follows: Section  2 illustrates the rationale of the paper; Section  3 reports on some pertinent related works; Section  4 introduces the relevant aspects of the 5S Model and of the DELOS Reference Model; Section  5 presents the semantic mapping between the 5S Model and the DELOS Reference Model associating the high level concepts of one model to those of the other; Section  6 to 11 respectively show the correspondences between the notions and domains of user, content, functionality, quality, policy and architectural component in the two models; Section  12 presents a relevant case of application of the proposed approach where users who interact with two DLS, that manage illuminated manuscripts, are interested in annotating their contents to perform activities of their interest. Section  13 sums up the results presented in the paper.