digital library a digital library digital repository or digital collection is an online database of digital objects that can include text still images audio video or other digital media formats objects can consist of digitized content like print or photographs as well as originally produced digital content like word processor files or social media posts in addition to storing content digital libraries provide means for organizing searching and retrieving the content contained in the collection digital libraries can vary immensely in size and scope and can be maintained by individuals or organizations history the early history of libraries is poorly documented but several key thinkers are connected to the emergence of this concept the establishment of the digital library was total dependent on the progress in the age of the internet it not only provided the means to compile the digital library but the access to the books by millions of individuals on the worldwide web vannevar bush and jcr licklider are two contributors that advanced this idea into then current technology bush was had supported research that led to the bomb that was dropped on hiroshima after seeing the disaster he wanted to create a machine that would show how technology can lead to understanding instead of destruction this machine would include a desk with two screens switches and buttons and a keyboard he named this the memex this way individuals would be able to access stored books and files at a rapid speed in 1956 ford foundation funded licklider to analyze how libraries could be improved with technology almost a decade later his book entitled libraries of the future included his vision he wanted to create a system that would use computers and networks so human knowledge would be accessible for human needs and feedback would be automatic for machine purposes this system contained three components the corpus of knowledge the question and the answer licklider called it a procognitive system early projects centered on the creation of an electronic card catalogue known as online public access catalog opac by the 1980s the success of these endeavors resulted in opac replacing the traditional card catalog in many academic public and special libraries this permitted libraries to undertake additional rewarding cooperative efforts to support resource sharing and expand access to library materials beyond an individual library an early example of a digital library is the education resources information center eric a database of education citations and abstracts which was created in 1964 and made available online through dialog in 1969 in 1994 digital libraries became visible due to a 244 million successful research proposals came from six us universities the universities included carnegie mellon university university of californiaberkeley university of michigan university of illinois university of californiasanta barbara and stanford university stanford research by sergeybrin and larrypage led to the founding of google early attempts at creating a model for digital libraries included the delos digital library reference model terminology the term digital libraries was first popularized by the nsfdarpanasa digital libraries initiative in 1994 with the availability of the computer networks the information resources are expected to stay distributed and accessed as needed whereas in vannevar bushs essay as we may think 1945 they ere to be collected and kept within the researchers memex the term virtual library was initially used interchangeably with digital library but is now primarily used for libraries that are virtual in other senses such as libraries which aggregate distributed content in the early days of digital libraries there was discussion of the similarities and differences among the terms digital virtual and electronic a distinction is often made between content that was created in a digital format known as borndigital and information that has been converted from a physical medium eg paper through digitization it should also be noted that not all electronic content is in digital data format the term hybrid library is sometimes used for libraries that have both physical collections and electronic collections for example american memory is a digital library within the library of congress some important digital libraries also serve as long term archives such as arxiv and the internet archive others such as the digital public library of america seek to make digital information from various institutions widely accessible online types of digital libraries institutional repositories many academic libraries are actively involved in building institutional repositories of the institutions 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 in contrast to the publication of research in commercial journals where the publishers often limit access rights institutional truly free and corporate repositories are sometimes referred to as digital libraries institutional repository software is designed for archiving organizing and searching a librarys content popular opensource solutions include dspace eprints digital commons and fedora commonsbased systems islandora and samvera digital archives physical archives differ from physical libraries in several ways traditionally archives are defined as containing primary sources of information typically letters and papers directly produced by an individual or organization rather than the secondary sources found in a library books periodicals etc having their contents organized in groups rather than individual items having unique contents the technology used to create digital libraries is even more revolutionary for archives since it breaks down the second and third of these general rules in other words digital archives or online archives will still generally contain primary sources but they are likely to be described individually rather than or in addition to in groups or collections further because they are digital their contents are easily reproducible and may indeed have been reproduced from elsewhere the oxford text archive is generally considered to be the oldest digital archive of academic physical primary source materials archives differ from libraries in the nature of the materials held libraries collect individual published books and serials or bounded sets of individual items the books and journals held by libraries are not unique since multiple copies exist and any given copy will generally prove as satisfactory as any other copy the material in archives and manuscript libraries are the unique records of corporate bodies and the papers of individuals and families a fundamental characteristic of archives is that they have to keep the context in which their records have been created and the network of relationships between them in order to preserve their informative content and provide understandable and useful information over time the fundamental characteristic of archives resides in their hierarchical organization expressing the context by means of the archival bond archival descriptions are the fundamental means to describe understand retrieve and access archival material at the digital level archival descriptions are usually encoded by means of the encoded archival description xml format the ead is a standardized electronic representation of archival description which makes it possible to provide union access to detailed archival descriptions and resources in repositories distributed throughout the world given the importance of archives a dedicated formal model called nested sets for object hierarchies nestor built around their peculiar constituents has been defined nestor is based on the idea of expressing the hierarchical relationships between objects through the inclusion property between sets in contrast to the binary relation between nodes exploited by the tree nestor has been used to formally extend the 5s model to define a digital archive as a specific case of digital library able to take into consideration the peculiar features of archives features of digital 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 can be much lower than that of a traditional library a physical library must spend large sums of money paying for staff book maintenance rent and additional books digital libraries may reduce or in some instances do away with these fees both types of library require cataloging input to allow users to locate and retrieve material digital libraries may be more willing to 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 conventional libraries may consider that providing online access to their op ac catalog is sufficient an important advantage to digital conversion is increased accessibility to users they also increase availability to individuals who may not be traditional patrons of a library due to geographic location or organizational affiliation no physical boundary the user of a digital library need not to go to the library physically people from all over the world can gain access to the same information as long as an internet connection is available round the clock availability a major advantage of digital libraries is that people can gain access 247 to the information multiple access the same resources can be used simultaneously by a number of institutions and patrons this may not be the case for copyrighted material a library may have a license for lending out only one copy at a time this is achieved with a system of digital rights management where a resource can become inaccessible after expiration of the lending period or after the lender chooses to make it inaccessible equivalent to returning the resource information retrieval the user is able to use any search term word phrase title name subject to search the entire collection digital libraries can provide very userfriendly interfaces giving click able access to its resources preservation and conservation digitization is not a longterm preservation solution for physical collections but does succeed in providing access copies for materials that would otherwise fall to degradation from repeated use digitized collections and borndigital objects pose many preservation and conservation concerns that analog materials do not please see the following problems section of this page for examples space whereas 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 them and media storage technologies are more affordable than ever before added value certain characteristics of objects primarily the quality of images may be improved digitization can enhance legibility and remove visible flaws such as stains and discoloration easily accessible software there are a number of software packages for use in general digital libraries for notable ones see digital library software institutional repository software which focuses primarily on ingest preservation and access of locally produced documents particularly locally produced academic outputs can be found in institutional repository software this software may be proprietary as is the case with the library of congress which uses digiboard and cts to manage digital content the design and implementation in digital libraries are constructed so computer systems and software can make use of the information when it is exchanged these are referred to as semantic digital libraries semantic libraries are also used to socialize with different communities from a mass of social networks djdl is a type of semantic digital library keywordsbased and semantic search are the two main types of searches a tool is provided in the semantic search that create a group for augmentation and refinement for keywordsbased search conceptual knowledge used in djdl is centered around two forms the subject ontology and the set of concept search patterns based on the ontology the three type of ontologies that are associated to this search are bibliographic ontologies communityaware ontologies and subject ontologies metadata in traditional libraries the ability to find works of interest is directly related to how well they were cataloged while cataloging electronic works digitized from a librarys existing holding may be as simple as copying or moving a record from the print to the electronic form complex and borndigital works require substantially more effort to handle the growing volume of electronic publications new tools and technologies have to be designed to allow effective automated semantic classification and searching while fulltext search can be used for some items there are many common catalog searches which cannot be performed using full text including finding texts which are translations of other texts differentiating between editionsvolumes of a textperiodical inconsistent descriptors especially subject headings missing deficient or poor quality taxonomy practices linking texts published under pseudonyms to the real authors samuel clemens and mark twain for example differentiating nonfiction from parody the onion from the new york times searching 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 oaipmh to expose their metadata to other digital libraries and search engines like google scholar yahoo and scirus can also use oaipmh to find these deep web resources there are two general strategies for searching a federation of digital libraries distributed searching and searching previously harvested metadata 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 z3950 are frequently used in distributed searching a benefit to this approach is that the resourceintensive 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 therefore 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 oaipmh 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 resourceintensive and therefore expensive digital preservation digital preservation digital preservation aims to ensure that digital media and information systems are still interpretable into the indefinite future also the materials are not preserved for the future the egranary is intended for use in places or situations where internet connectivity is very slow nonexistent unreliable unsuitable or too expensive 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 digitize millions of books per year google bookscanning project is also working with libraries to offer digitize books pushing forward on the digitize book realm copyright and licensing 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 twentythree 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 seventytwo 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 fair use provisions 17 usc 107 under the copyright act of 1976 provide specific guidelines under which circumstances libraries are allowed to copy digital resources four factors that constitute fair use are purpose of the use nature of the work amount or substantiality used and market impact 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 see also above 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 copyright issues persist as such proposals have been put forward suggesting that digital libraries be exempt from copyright law although this would be very beneficial to the public it may have a negative economic effect and authors may be less inclined to create new works another issue that complicates matters is the desire of some publishing houses to restrict the use of digit materials such as ebooks purchased by libraries whereas with printed books the library owns the book until it can no longer be circulated publishers want to limit the number of times an ebook can be checked out before the library would need to repurchase that book while from a publishing perspective this sounds like a good balance of library lending and protecting themselves from a feared decrease in book sales libraries are not set up to monitor their collections as such they acknowledge the increased demand of digital materials available to patrons and the desire of a digital library to become expanded to include best sellers but publisher licensing may hinder the process recommendation systems many digital libraries offer recommender systems to reduce information overload and help their users discovering relevant literature some examples of digital libraries offering recommender systems are ieee xplore europeana and gesis sowiport the recommender systems work mostly based on contentbased filtering but also other approaches are used such as collaborative filtering and citationbased recommendations typically digital libraries develop and maintain their own recommender systems based on existing search and recommendation frameworks such as apache lucene or apache mahout however there are also some recommendationasaservice provider specializing in offering a recommender system for digital libraries as a service drawbacks of digital libraries digital libraries or at least their digital collections unfortunately also have brought their own problems and challenges in areas such as user authentication for access to collections copyright digital preservation see above equity of access see digital divide interface design interoperability between systems and software information organization inefficient or nonexistent taxonomy practices especially with historical material training and development quality of metadata exorbitant cost of buildingmaintaining the terabytes of storage servers and redundancies necessary for a functional digital collection there are many large scale digitisation projects that perpetuate these problems future development large scale digitization projects are underway at google the million book project and internet archive with continued improvements in book handling and presentation technologies such as optical character recognition and development of alternative depositories and business models digital libraries are rapidly growing in popularity just as libraries have ventured into audio and video collections so have digital libraries such as the internet archive google books project recently received a court victory on proceeding with their bookscanning project that was halted by the authors guild this helped open the road for libraries to work with google to better reach patrons who are accustomed to computerized information according to larry lannom director of information management technology at the nonprofit corporation for national research initiatives cnri all the problems associated with digital libraries are wrapped up in archiving he goes on to state if in 100 years people can still read your article well have solved the problem daniel akst author of the webster chronicle proposes that the future of libraries and of information is digital peter lyman and hal variant information scientists at the university of california berkeley estimate that the worlds total yearly production of print film optical and magnetic content would require roughly 15 billion gigabytes of storage therefore they believe that soon it will be technologically possible for an average person to access virtually all recorded information bibliographic database digital library federation dlib a magazine dedicated to digital library research and development digital humanities fulltext database mobile library online encyclopedia traveling library candela l castelli d pagano history evolution and impact of digital libraries in p iglezakis i synodinou t kapidakis s ed epublishing and digital libraries legal and organizational issues igi global 2011 1 30 a description of the initiatives and understandings leading to digital libraries wikiversity has learning resources about curriculum on digital libraries wikimedia commons has media related to digital libraries authority control gnd 43809406 lccn sh95008857 ndl 00831135 