SI in Digital Libraries
D igital libraries can be viewed as infra-structures for supporting the creation of information sources, facilitating the movement of information across global networks, and allowing the effective and efficient interaction among knowledge producers , librarians, and information and knowledge seekers. Typically, a digital library is a vast collection of objects stored and maintained by multiple information sources, including databases, image banks, file systems, email systems, the Web, and other methods and formats. Often, these information sources are heterogeneous, in terms of how the objects are stored, organized and managed, and the platforms on which they reside. Moreover, the information sources are dynamic in the sense they may be either included in or removed from the digital library system. Furthermore, digital libraries are composite multimedia objects comprising different media components including text, video, images, or audio. Therefore, the challenge is to provide users with the ability to seamlessly and transparently access digital library objects in spite of the heterogeneity and dynamism among the information sources, and the composite multimedia nature of the objects. To accomplish this, the problem of heterogeneity and SI must first be resolved. Although there have been several techniques proposed by the research community, especially the database and agent communities, these techniques cannot be easily adapted to digital library environments. This is because, while database integration primarily deals with structured textual data, SI in digital libraries requires the ability to deal with massive amount of multimedia objects. In this article, we identify research challenges involved with SI that are specific to digital libraries, discuss the available solutions that meet the digital library requirements and the digital library prototypes, and describe the environmental digital library system under development at the Cen-Issues in SI In general, system integration includes pre-integration , identification of schema matching, schema integration, and source-data integration sub-processes [6, 10]. The pre-integration process deals with transforming the data models used within the underlying information sources into a " common " model. A common model that can represent all the models at the underlying sources is essential to resolving integration problems due to the heterogeneity in data models such as relational, object-oriented, and hierarchical formats. Therefore, the first task in the pre-integration process is to identify the different data models and extract their schema. Since this is normally a one-time task, manual efforts are often used. The next task is to select a data model as the common …