Digital library

A digital library is a library in which a significant proportion of the resources are available in machine-readable format (as opposed to print or microform), accessible by means of computers. The digital content may be locally held or accessed remotely via computer networks. In libraries, the process of digitization began with the catalog, moved to periodical indexes and abstracting services, then to periodicals and large reference works, and finally to book publishing. Some of the largest digital libraries are purely digital having few if any physical holdings.

Types of Digital Libraries

The term Digital Library is diffuse enough to be applicable to a wide range of digital entities. Divisions can be made between libraries that have some physical presence where patrons are able to access physical holdings as well as digital holdings and libraries where collections are almost completely digital. Project Gutenberg, ibiblio and the Internet Archive can serve as examples of this later case.

Advantages

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.
* 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 to the information at any time, night or day.
* Multiple accesses. The same resources can be used at the same time by a number of users.
* Structured approach. Digital libraries provide access to much richer content in a more structured manner, i.e. we can easily move from the catalog to the particular book then to a particular chapter and so on.
* Information retrieval. The user is able to use any search term bellowing to the word or phrase of the entire collection. Digital libraries can provide very user-friendly interfaces, giving clickable access to its resources.
* Preservation and conservation. An exact copy of the original can be made any number of times without any degradation in quality.
* 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. When a library has no space for extension digitization is the only solution.
* Networking. A particular digital library can provide a link to any other resources of other digital libraries very easily; thus a seamlessly integrated resource sharing can be achieved.
* Cost. In theory, the cost of maintaining a digital library is 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. Although digital libraries do away with these fees, it has since been found that digital libraries can be no less expensive in their own way to operate. Digital libraries can and do incur large costs for the conversion of print materials into digital format, for the technical skills of staff to maintain them, and for the costs of maintaining online access (i.e servers, bandwidth costs, etc.). Also, the information in a digital library must often be "migrated" every few years to the latest digital media. This process can incur very large costs in hardware and skilled personnel.(See data migration).

Disadvantages

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. 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 2000B.C. to 1960, has been made [1].

Other digital libraries (more specifically, digitial collections, which may be acquired by 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.

Digital libraries cannot reproduce the environment of a traditional library. Many people also find reading printed material to be easier than reading material on a computer screen although this depends heavily on presentation as well as personal preferences[2]. Also, due to technological developments, a digital library can see some of its content become out-of-date and its data may become unaccessible.

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 digitial library, many of those who could most benefit from its global reach (for instance in the Third World) are not able to do so.

Academic Repositories

Many academic libraries are actively involved in building institutional repositories of the institution's books, papers, theses, and other works which can be digitized. Many of these repositories are made available to the academic community or the general public. Insitutional repositories are often referred to as digital libraries.

Digital Archives

Archives differ from libraries in several ways. Traditionally, archives were 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, etc);# Having their contents organized in groups rather than individual items. Whereas books in a library are cataloged individually, items in an archive are typically grouped by provenance (the individual or organization who created them) and original order (the order in which the materials were kept by the creator);# Having unique contents. Whereas a book may be found at many different libraries, depending on its rarity, the records in an archive are usually one-of-a-kind, and cannot be found or consulted at any other location except at the archive that holds them.

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 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.

Cornell University and the Wisconsin Historical Society are considered leaders in the field of digital archive creation and management.

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 (OAI-PMH) to expose their metadata to other digital libraries, and search engines like Google 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, 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 or eliminated or clustered, and the remaining items are sorted and presented back to the client. Scalability and performance issues tend to plague distributed searching for large federations of digital libraries. Protocols like Z39.50 are frequently used in distributed searching.

Searching over previously harvested metadata requires the pooling of metadata collected from every digital library in the federation. This solution scales better than distributed search, but it introduces the problem of data freshness; digital libraries need to be re-harvested on a periodic basis to discover new and updated resources. OAI-PMH is frequently used by digital libraries for harvesting metadata.

Framework

Here we will discuss the framework of a digital library to understand the internal structure of some digital library. I will give the example of Greenstone Digital Library Software which is free and open source digital library building software

The future

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.

External links

* European NAvigator: The first Digital Library on the history of the European Union
*dLIST dLIST: Digital Library of Information Science and Technology, an open access archive of Information Sciences materials
*DL-Harvest DL-Harvest, an open access aggregator for Information Sciences
*Demonstration library using hypercompressed CPC format
*D-Lib Magazine Electronic publication that primarily focuses on digital library research and development
*Digital Libraries by William Y. Arms Available on-line
*Kitab.az Azerbaijan Electronic Library Network (Kitab.Az) Azerbaijan's online network of electronic catalogues of leading Azerbaijan universities and specialised libraries and online library
*Bookyards - Library To The World Free Ebooks
*National Science Digital Library (NSDL) The United States' online library of resources for science, technology, engineering, and mathematics education and research
*PublicLiterature.org - Digital collection of books, poems, religious and reference texts.
*The International Children's Digital Library
*eLibrary - Open Ebooks Directory
*Scholarly Electronic Publishing Bibliography
*The Online Books Page Search for free online books by author, title, keyword, etc.
*The Internet Public Library Search for free online books by author, title, keyword, etc.
*The eGranary Digital Library Millions of digital resources for those with inadequate Internet connectivity.
*Search engines which search digital libraries
*UK Higher Education & Research Libraries (link list maintained at Exeter University by Ian Tilsed)
*Online version of Internetworking Technologies, by Rahul Banerjee, which deals with the architectures of leading digital libraries in the world (chapter 10)
*Library of Anarachy: Collection Of Technology Book (Under Development)
*The Scope of the Digital Library
*Demonstration library utilizing extreme compression
* The American Journeys Project an example of a digital library whose contents center on a particular theme--the exploration of North America.
*www.nirvanastorage.com Build your own digital library using the Storage Resource Broker (SRB)
*Kabbalah Digital Library One of the largest multi-language collections of ancient and modern Kabbalistic writings.
*Free e-books

Digital library: Encyclopedia BETA

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