Towards a Formal Theory for Complex Objects and Content-Based Image Retrieval

Advanced services in digital libraries (DLs) have been developed and are widely used to address the required capabilities of an assortment of systems as DLs expand into diverse application domains. In order to reuse, integrate, unify, manage, and support these heterogeneous resources, the notion of complex objects (COs) has emerged as a means to facilitate aggregation of content and to help developers to manage heterogeneous information resources, and their internal components. In particular, complex image objects (along with the most used service Content-Based Image Retrieval) have the potential to play a key role in information systems, due to the large availability of images and the need to integrate them with other datasets (and metadata), and image manipulation software. However, the lack of consensus on precise theoretical definitions for these concepts usually leads to ad hoc implementation, duplication of efforts, and interoperability problems. In this article we exploit the 5S Framework to propose a formal description for Complex Objects and Content-Based Image Retrieval, defining their fundamental concepts and relationships from a digital library (DL) perspective. These formalized concepts can be used to classify, compare, and highlight the differences among components, technologies, and applications, impacting digital library researchers, designers, and developers. The theoretical extensions of digital library functionality presented here cover complex image objects, within a practical case study, to exemplify the integrative use of services, thus balancing theory and practice.