The design and architecture of digital libraries

Digital Library Systems (DLSes) are software systems that support the operation of a digital library. As software systems, they are designed primarily to meet the needs of the target community using current best practices in software design and architecture. Digital libraries, like other disciplines, also asserts a set of design constraints that then affect the architectural choices for these digital library systems. Key constraints include: generality, usability by different communities, interoperability, extensibility, preservation and scalability. Individually, these are not unique to DLSes, but together they provide a framework for the development of specific DL architectures. The DELOS Digital Library Manifesto (Candela, et al, 2007) defines three actors in the architectural space of DLSes. The Digital Library System is the software system that manages data and provides services to users. The Digital Library focuses on the collection, users, processes and services; with a DLS as one of its operational systems. Finally, the Digital Library Management System (DLMS) is responsible for the management of the DLS, for example instantiation of collections and services. This chapter focuses on the DLS and, to a lesser degree, the DLMS. Core design considerations are first presented, followed by how these principles are realised in modern reusable and custom-built DLSes. The next section deals with how these individual systems are interconnected into larger networked DLSes, exemplified by international projects such as NDLTD. Scalability – how to deal with increasing sizes of data and increasing numbers of service requests – is then discussed. Finally, the chapter ends with research directions and a case study of an architecture designed for the developing world.