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. The digital content may be stored locally, or accessed remotely via computer networks. A digital library is a type of information retrieval system.
A digital library has a number of advantages and problems not found in a traditional library. Some of the advantages are that there are no physical limits to information storage, materials can be accessed around the clock by multiple users, and they feature efficient information retrieval mechanisms. Some of the problems unique to a digital library include the need for periodical data migration due to constant and rapid technological advancement of information technology, as well as issues concerning copyright infringement. Nevertheless, library and information professional communities are pursuing a workable model of a digital library and a number of initiatives have been made both in the public and private sectors. For example, Google collaborated with a number of major academic libraries and made a large number of library holdings available to internet users under the Google Books Library Project.
The first use of the term "digital library" in print may have been in a 1988 report to the Corporation for National Research Initiatives The term "digital libraries" was first popularized by the NSF/DARPA/NASA Digital Libraries Initiative in 1994. 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 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, only some web sites can be considered true digital libraries. 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, for example, 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 (such as letters) to be cataloged, 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 CMU's Universal library are considered leaders in the field of digital archive creation and management. There are hundreds of regional digital archives, such as the Wisconsin Historical Society. The Vatican maintains an extensive digital library inventory and associated technology. The entire works of Martin Luther are held at Emory University and are being digitized under an $8M Grant from Coca-Cola heirs, and the Packard Foundation maintains digitization facilities near the Acropolis in Athens, Greece.
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 too 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.
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.
A digital library can be built around specific repository software. The best known examples of this are DSpace, Eprints, Fedora, dLibra, and Greenstone Digital Library Software.
A strategy with defined selection priorities for digitization is critical and should be informed by a convergence in the consideration for both preservation and access. The focus should be based on traditional preservation decisions such as the value of materials; the condition of materials; use of materials; and material characteristics ensuring a high level of success. For the Library of Congress, for example, items of national interest are prime candidates and digitizing these objects improves access while reducing the wear and tear on the originals.
In the early discussions about digitization of library materials, the selection decisions were proposed based on a desire for better access to that item's content and not on the condition or value of the original item. In 2001, Paula De Stefanowrote that a use-based criteria was promising, as it is “fundamental to collection development and is the common thread in all selection decisions” however her own study showed that use was not the most popular approach—in fact, most digital projects at the time focused on special collections, which are generally not the most popular items in the overall collection.
The persistent risk of disappearing "last copies" and the declines seen in the condition of national treasures, as exemplified by the 2005 Heritage Health Index Report on the State of America's Collections provide the rationale for establishing priorities and balancing access with preservation needs. The transient nature of electronic information can contribute to a phenomenon called "memory loss." This is a result of data extinctions as technologies become obsolete. There is also a drift away from original bibliographic contexts as time passes. A 1998 Council on Library and Information Sources white paper identified the following comprehensive considerations for selection: Assessment of the intellectual and physical nature of the source materials; the number and location of current and potential users; the current and potential nature of use; the format and nature of the proposed digital product and how it will be described, delivered, and archived; how the proposed product relates to other digitization efforts; and projections of costs in relation to benefits.
Digitization is the process of representing an object, an image, or a signal (usually an analog signal) by a discrete set of its points or samples. The result is called "digital representation" or, more specifically, a "digital image," for the object, and "digital form," for the signal.
Analog signals are continuously variable, both in the number of possible values of the signal at a given time, as well as in the number of points in the signal in a given period of time. However, digital signals are discrete in both of those respects, and so a digitization can only ever be an approximation of the signal it represents. The digital representation does not necessarily lose information in this transformation since the analog signal usually contains both information and noise.
A digital signal may be represented by a sequence of integers. Digitization is performed by reading an analog signal, A, and, at regular time intervals (sampling frequency), representing the value of A at that point by an integer. Each such reading is called a sample.
A series of integers can be transformed back into an analog signal that approximates the original analog signal. Such a transformation is called DA conversion. There are two factors determining how close such an approximation to an analog signal A a digitization D can be, namely the sampling rate and the number of bits used to represent the integers.
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.
There are many collaborative digitization projects throughout the United States and in Europe, Australia, and Asia. Two of the earliest projects were the Collaborative Digitization Project, in Colorado, and NC ECHO, North Carolina Exploring Cultural Heritage Online, based at the State Library of North Carolina. These projects helped to establish and publish best practices for digitization and work with regional partners to digitize cultural heritage materials. Additional criteria for best practice have more recently been established in the UK, Australia, and the European Union. Recollection Wisconsin, formerly Wisconsin Heritage Online, is a collaborative digitization project modeled after the Colorado Collaborative Digitization Project. They collaborate with libraries, archives, historical societies, and museums across Wisconsin to facilitate digitization efforts. Their digitization guidelinesGeorgia's collaborative digitization program, the Digital Library of Georgia, presents a seamless virtual library on the state's history and life, including more than a hundred digital collections from 60 institutions and 100 agencies of government. The Digital Library of Georgia is a GALILEO initiative based at the University of Georgia Libraries.
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.
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 such as repurchase of lost books, facilities, and additional facility maintenance fees. Digital libraries do away with some of 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 and availability for individuals who may not be traditional patrons of a library, due to geographic location or organizational affiliation.
Technological standards change over time and forward data migration must be a constant consideration of every library. Data migration is a means of transferring an unstable digital object to another more stable format, operating system, or programming language. Data 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, data migration becomes this never-ending race to transfer digital objects to new and more stable formats. Data 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. 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.
Digital libraries are hampered by copyright law because, unlike with traditional printed works, the laws of digital copyright are still being formed. The republication of material on the web by libraries may require permission from rights holders, and there is a conflict of interest between libraries and the publishers who may wish to create online versions of their acquired content for commercial purposes. In 2010, it was estimated that twenty-three percent of books in existence were created before 1923 and thus out of copyright. Of those printed after this date, only five percent were still in print as of 2010. Thus, approximately seventy-two percent of books were not available to the public.
There is a dilution of responsibility that occurs as a result of the distributed nature of digital resources. Complex intellectual property matters may become involved since digital material is not always owned by a library. 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.
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.
Some digital libraries acquire a license to lend their resources. This may involve the restriction of lending out only one copy at a time for each license, and applying a system of digital rights management for this purpose.
The Digital Millennium Copyright Act of 1998 was an act created in the United States to attempt to deal with the introduction of digital works. This Act incorporates two treaties from the year 1996. It criminalizes the attempt to circumvent measures which limit access to copyrighted materials. It also criminalizes the act of attempting to circumvent access control. This act provides an exemption for nonprofit libraries and archives which allows up to three copies to be made, one of which may be digital. This may not be made public or distributed on the web, however. Further, it allows libraries and archives to copy a work if its format becomes obsolete.
All links retrieved October 23, 2017.
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