Digital libraries are collections of digital content and services selected by a curator for use by a particular user community. Digital libraries offer direct access to the content of a wide variety of intellectual works, including text, audio, video, and data; and may offer a variety of services supporting search, access, and collaboration. In the last decade digital libraries have rapidly become ubiquitous because they offer convenience, expanded access, and search capabilities not present in traditional libraries. This has greatly altered how library users find and access information, and has put pressure on traditional libraries to take on new roles. However, information professionals have raised compelling concerns regarding the sizeable gaps in the holdings of digital libraries, about the preservation of existing holdings, and about sustainable economic models. This chapter presents an overview of the history, advantages, disadvantages, and design principles relating to digital libraries, and highlights important controversies and trends. For an excellent comprehensive discussion of the use, cost and benefits of digital libraries see Lesk (2005), for further discussion of architectural and design issues see Arms (2000), and see Witten and Bainbridge (2002) for a detailed example of the mechanics of implementing a digital library.
Key Terms in this Chapter
Digital Repository: A managed system for long-term digital objects. Also, Institutional repositories are a type of digital repository that is designated by an institution for the preservation of digital objects produced under its aegis.
Work/Edition/Manifestation/Item Hierarchy: A set of principles for distinguishing between a distinct work of intellectual creation (e.g., Beethoven’s 5th Symphony), the edition of that work (e.g., the 1979 performance by the Vienna Symphony orchestra), the manifestation of that work (e.g. an MP3 file created with a 192 bit sampling create settings), and a particular item (e.g., a copy of that MP3 file that resides in a particular repository).
Metadata: Metadata is often defined as data about data. More specifically, it is information that refers to other digital objects. Metadata often consists of descriptive information (such as a title), administrative information (such as a description of the rights required to view the object), and structural information (such as the organization of page images within a larger book). Metadata can be derived from the object itself in order to used as a surrogate for searching and other services, but is more often information that is not contained in the object itself.
Universal Numeric Fingerprint: A universal numeric fingerprint is used to guarantee that a two digital objects (or parts thereof) in different formats represent the same intellectual object (or work). UNFs are formed by generating an approximation of the intellectual content of the object, putting this in a normalized form, and applying a cryptographic hash to produce a unique key. (Altman, et al. 2003)
Union Catalog: An online public access catalog (OPAC) formed by indexing descriptive metadata for each item in the library. In the digital library, Union Catalogs are increasingly being supplemented or replaced by a combination of distributed search across multiple independent catalogs, and direct indexing of digital object content.
Simple/Complex Objects: Simple digital objects consist of a single file that can be fully understood by the user and represented by the user’s software. Complex digital objects require multiple separate files, and possibly additional metadata, to be properly understood.
Born Digital vs. Digitized Objects: Objects that were born digital were created originally in digital forms, for example a word processing file. Digitized objects were created from non-digital forms (e.g., via optically scanning a paper book).