A digital library is a library in which collections are stored in digital formats (as opposed to print, microform, or other media) and accessible by computers.[1] The digital content may be stored locally, or accessed remotely via computer networks. A digital library is a type of information retrieval system.
The first use of the term digital library in print may have been in a 1988 report to the Corporation for National Research Initiatives[2] The term digital libraries was first popularized by the NSF/DARPA/NASA Digital Libraries Initiative in 1994.[3] The older names electronic library or virtual library are also occasionally used, though electronic library nowadays more often refers to portals, often provided by government agencies, as in the case of the Florida Electronic Library. The DELOS Digital Library Reference Model[4] defines a digital library as:
An organization, which might be virtual, that comprehensively collects, manages and preserves for the long term rich digital content, and offers to its user communities specialized functionality on that content, of measurable quality and according to codified policies.
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The term digital library is diffuse enough to be applied to a wide range of collections and organizations, but, to be considered a digital library, an online collection of information must be managed by and made accessible to a community of users. Thus, some web sites can be considered digital libraries, but far from all. Many of the best known digital libraries are older than the web including Project Perseus, Project Gutenberg, and ibiblio. Nevertheless, as a result of the development of the internet and its search potential, digital libraries such as the European Library and the Library of Congress are now developing in a Web-based environment. Public, school and college libraries are also able to develop digital download websites, featuring eBooks, audiobooks, music and video, through companies like OverDrive, Inc.
A distinction is often made between content that was created in a digital format, known as born-digital, and information that has been converted from a physical medium, e.g., paper, by digitizing. The term hybrid library is sometimes used for libraries that have both physical collections and digital collections. They consist of a combination of traditional preservation efforts such as microfilming and new technologies involving digital projects. For example, American Memory is a digital library within the Library of Congress. Some important digital libraries also serve as long term archives, for example, the ePrint arXiv, and the Internet Archive.
Many academic libraries are actively involved in building institutional repositories of the institution's books, papers, theses, and other works which can be digitized or were 'born digital'. Many of these repositories are made available to the general public with few restrictions, in accordance with the goals of open access. Institutional, truly free, and corporate repositories are often referred to as digital libraries.
Archives differ from libraries in several ways. Traditionally, archives were defined as:
The technology used to create digital libraries has been even more revolutionary for archives since it breaks down the second and third of these general rules. The use of search engines, Optical Character Recognition and metadata allow digital copies of individual items (i.e. letters) to be catalogued, and the ability to remotely access digital copies has removed the necessity of physically going to a particular archive to find a particular set of records. The Oxford Text Archive is generally considered to be the oldest digital archive of academic primary source materials.
Project Gutenberg, Google Book Search, Windows Live Search Books, Internet Archive, Cornell University, The Library of Congress World Digital Library, The Digital Library at the University of Michigan, and Carnegie Mellon University's Million Book Project are considered leaders in the field of digital archive creation and management. There are hundreds of regionals such as the Wisconsin Historical Society. The Vatican maintains an extensive digital library inventory and associated technology. The Packard Foundation maintains digitization facilities near the Acropolis in Athens, Greece, as examples.
Large scale digitization projects are underway at Google, the Million Book Project, MSN, and Yahoo!. With continued improvements in book handling and presentation technologies such as optical character recognition and ebooks, and development of alternative depositories and business models, digital libraries are rapidly growing in popularity as demonstrated by Google, Yahoo!, and MSN's efforts. Just as libraries have ventured into audio and video collections, so have digital libraries such as the Internet Archive.
Most digital libraries provide a search interface which allows resources to be found. These resources are typically deep web (or invisible web) resources since they frequently cannot be located by search engine crawlers. Some digital libraries create special pages or sitemaps to allow search engines to find all their resources. Digital libraries frequently use the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) to expose their metadata to other digital libraries, and search engines like Google Scholar, Google, Yahoo! and Scirus can also use OAI-PMH to find these deep web resources.[5]
There are two general strategies for searching a federation of digital libraries:
Distributed searching typically involves a client sending multiple search requests in parallel to a number of servers in the federation. The results are gathered, duplicates are eliminated or clustered, and the remaining items are sorted and presented back to the client. Protocols like Z39.50 are frequently used in distributed searching. A benefit to this approach is that the resource-intensive tasks of indexing and storage are left to the respective servers in the federation. A drawback to this approach is that the search mechanism is limited by the different indexing and ranking capabilities of each database, making it difficult to assemble a combined result consisting of the most relevant found items.
Searching over previously harvested metadata involves searching a locally stored index of information that has previously been collected from the libraries in the federation. When a search is performed, the search mechanism does not need to make connections with the digital libraries it is searching - it already has a local representation of the information. This approach requires the creation of an indexing and harvesting mechanism which operates regularly, connecting to all the digital libraries and querying the whole collection in order to discover new and updated resources. OAI-PMH is frequently used by digital libraries for allowing metadata to be harvested. A benefit to this approach is that the search mechanism has full control over indexing and ranking algorithms, possibly allowing more consistent results. A drawback is that harvesting and indexing systems are more resource-intensive and therefore expensive.
See also Digital Collections Selection Criteria.
A digital library can be built around specific repository software. The best known examples of this are DSpace, Eprints, Fedora, dLibra(Poland), and Greenstone Digital Library Software.
The Reference Model for an Open Archival Information System (OAIS) provides a framework to address Digital preservation. [6]
Other formal frameworks include the DELOS Reference Model(Agosti, et al., 2006)[7] and the Streams, Structures, Spaces, Scenarios, Societies (5S) formal framework (Gonçalves, Fox, Watson, & Kipp, 2004)[8]
In the past few years, procedures for digitizing books at high speed and comparatively low cost have improved considerably with the result that it is now possible to plan the digitization of millions of books per year for creating digital libraries.[9]
See also Digitizing#Collaborative digitization projects.
The advantages of digital libraries as a means of easily and rapidly accessing books, archives and images of various types are now widely recognized by commercial interests and public bodies alike.[10] You can also access any user account simply through a link like this.
Traditional libraries are limited by storage space; digital libraries have the potential to store much more information, simply because digital information requires very little physical space to contain it. As such, the cost of maintaining a digital library is much lower than that of a traditional library. A traditional library must spend large sums of money paying for staff, book maintenance, rent, and additional books. Digital libraries do away with these fees.
Digital libraries can immediately adopt innovations in technology providing users with improvements in electronic and audio book technology as well as presenting new forms of communication such as wikis and blogs. An important advantage to digital conversion is increased accessibility to users. There in also availability to individuals who may not be traditional patrons of a library, due to geographic location or organizational affiliation.
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With the ever-expanding digital collections in today’s library’s and archives we are facing new preservation challenges that seem to have no concrete solutions or universal standards in which to guide us. For centuries we have seen the evolution of paper based materials and have been able to successfully meet many of the challenges that these materials present to the realm of preservation. Our digital world, however, is far too young and mercurial to have any long-term sense of how this new media can be preserved for long-term future access.
On one hand multiple copies of a physical volume can exist in different libraries, but can only be viewed by visiting the library or repository directly. On the other hand, a digital object can be viewed from multiple locations but more than likely exists only as a single copy in a single location on one server.[12] Access to digital libraries and their collections is dependent upon a stable information technology infrastructure (power, computers, communications links etc.). Hence, despite the egalitarian potential of the digital library, many of those who could most benefit from its global reach (for instance in the Third World) are not able to do so. Smaller libraries and repositories in developed countries may also have limited resources in dealing with long term digitization projects. There are complex technological steps involved with capturing images, and librarians must evaluate the ability to commit to long term projects.[13]
Technological standards change over time and forward migration must be a constant consideration of every library. Migration is a means of transferring an unstable digital object to another more stable format, operating system, or programming language.[14] Migration allows the ability to retrieve and display digital objects that are in danger of becoming extinct. This is a rather successful short-term solution for the problem of aging and obsolete digital formats, but with the ever-changing nature of computer technologies, migration becomes this never-ending race to transfer digital objects to new and more stable formats. Migration is also flawed in the sense that when the digital files are being transferred, the new platform may not be able to capture the full integrity of the original object.[15] There are countless artifacts sitting in libraries all over the world that are essentially useless because the technology required to access the source is obsolete. In addition to obsolescence, there are rising costs that result from continually replacing the older technologies. This issue can dominate preservation policy and may put more focus on instant user access in place of physical preservation.[16]
Some people have criticized that digital libraries are hampered by copyright law, because works cannot be shared over different periods of time in the manner of a traditional library. There is a dilution of responsibility that occurs as a result of the spread-out nature of digital resources. Complex intellectual property matters may become involved since digital material isn't always owned by a library.[17] The content is, in many cases, public domain or self-generated content only. Some digital libraries, such as Project Gutenberg, work to digitize out-of-copyright works and make them freely available to the public. An estimate of the number of distinct books still existent in library catalogues from 2000BC to 1960, has been made.[18][19]
Other digital libraries accommodate copyright concerns by licensing content and distributing it on a commercial basis, which allows for better management of the content's reproduction and the payment (if required) of royalties. The Fair Use Provisions (17 USC § 107) under copyright law provide specific guidelines under which circumstances libraries are allowed to copy digital resources. Four factors that constitute fair use are purpose of use, nature of the work, market impact, and amount or substantiality used.[20]
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