Digital Library: The IT has almost converted the whole world into a global village.  The revolution in the IT sector is influencing the information industry at its peak and revolutionized the concept of libraries where it has been used extensively to record, store, and disseminate the information in the digital form. Each and every library step by step shifts over to this dimension to meet the demand put on it.

If one considers that the information is for use and for all then why should not libraries be for all? Why should libraries not become universal for all those who seek information, considering that a large number of organization in the USA and Europe has already more or less switched over to digital mode i.e. they are making the digitized images of periodical which are not available in electronic format and there after no new procurement are being made on print media. Example of such organization are University of Micrographic Inc (UMI of USA), National Institute of Scientific and Technical Information (INIST of France), etc.

A twenty first century library if not at all digitized, has at least a section devoted to accessing the growing collection of computer readable materials, the subscribed bibliographic and full text database, E-Journal, etc. for the end user. Along with the access of the subscribed databases it also provides the Internet browsing and searching, E-Mail, Chat, Video Conferencing facilities to the user. Sometimes it also provides OPAC terminals. The downloaded articles can be printed upon request. Back issues of selected journals and newspapers are also available in some library as microfiche or microfilm, with readers and printers provided for access. All these collection together constitute the digital library.

A digital library is nothing but a large database of organized collection of multimedia, data that are globally available directly or indirectly across a network and eventually act as a portal site providing access to digital collections held elsewhere for the people who are working on hypertext environment.

Electronic resources accessible on the web for free or for a fee are undeniably major and important constituent of a digital library. To build a digital library all these resources need to go through the process of  selection, acquisition (by way of linking) and management. The information contents of a digital library, depending on the media type, may include a combination of structured / unstructured text, numerical data, scanned images, graphics, audio and video recordings. Different types of resources need to be handled differently in digital library environment.

1. Definition: In 1938 H. G. Wells dreamed of a world encyclopedia in which all-human knowledge would be available elsewhere. Today Internet in collaboration with digital libraries are moving fast to fulfill the dream of H. G. Wells.

The term "Digital Library" has a variety of potential meanings, ranging from a digitized collection of material that one might find in a traditional library to the collection of all digital information along with the services that make that information useful to all possible users. In simple a DL is a library having all it’s holding in the digital form or in a form that can be stored, processed by the computer system. It is nothing but a large database for the people who are working on hypertext environment. It is a system of organized collection of multimedia, data that are globally available directly or indirectly across a network.

According to Lesk (1997) “Digital libraries are organized collections of digital information. They combine the structuring and gathering of information, which libraries and archives have always done, with the digital representation that computers have made possible”.

According to Arms a digital library is a managed collection of information with associated services where the information is stored in digital format and accessible over a network.

The digital library federation in the USA defines the digital library as Digital libraries are organizations that provide the resources, including the specialized staff, to select, structure, offer intellectual access to, interpret, distribute, preserve the integrity of, and ensure the persistence over time of collections of digital works so that they are readily and economically available for use by a defined community or set of communities.

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. It comprises digital collections, services and infrastructure to support lifelong learning, research, scholarly communication and preservation. It is an environment which supports full life cycle of creation, storage, preservation, dissemination and use of data, and information. It is a process of democratization of information.

Project Gutenberg, Google Book Search, 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.

2. Characteristic: A digital library is an organized collection of digitized material or its holding in the digital form which can be accessible by a computer on the network by using TCP/IP or other protocol. The main characteristics of digital libraries are as follows

a) The function of acquisition, storage, preservation, retrieval is carried out through the use of digital technology.

b) Organized collection of information objects may be a digital text or any other.

c) Resources are available in computer readable form.

d) Access to the entire collection is globally available directly or indirectly across network.

e) Support users in dealing with information objects.

3. Need for a Digital Library: Digital libraries are needed to provide quality based service at the user desktop.

a) Easy to Understand: The visual or graphical information system of digital libraries is more popular as compared to text based information system.

b) Shifting of the Environment: The new generation user becomes only happy when they will be able to read from the computer screen. The new generation whose demand for information is never met demands that traditional libraries should be developed as a well equipped and interconnected DL.

c) Multiple Function of Same Information: In case of digital libraries by using hypertext it is possible to structure and organize the same digital information in a variety of ways which serve multiple functions.

d) Information Explosion: Digital library is expected to be able to handle the problem of information explosion somehow. It will be able to handle and manage large amount of digital content by simply providing link, without actually procuring the document.

e) Searching Problem in Traditional Libraries: By using digital library one will be able to retrieve information specifically for e.g. a particular image, photo, a definition, etc.

f) Distance Learning: Time is a major factor for each modern user of the library which is otherwise spent in coming and going to the library, but digitization will facilitate learning from home, office or other places which are convenient to users.

g) To Provide Access to Online Publication: As more and more information are published over internet, digital library needs to procure and provide link to the online publication and other important sources of information.

h) Limited Buying Power of Libraries: The collection of every library is limited to only a fraction of the total. Introduction of digital library will help to enhance the collection considerably.

i) Storage Problem in Traditional Libraries: Libraries are spending much of its budget by way of maintaining the collection in a usable form that also demands a huge physical space. Digitization hopes to overcome this. Digital Medias comes with a huge storage capacity.

j) Low Cost of Technology: The cost of technologies is much more less than that of traditional libraries.

k) Environmental Factor: The use of digital libraries is one of the cleanest technologies to fulfill the slogan “Burn a CD-ROM save a tree”.

4. Requirement for Digital Libraries: The internet and World Wide Web provide the impetus and technological environment for the development and operation of a digital library. The internet provides the TCP/IP and or its associated protocol for accessing the information and web provides tools and technique for publishing the information over internet. Still, for introducing any digital libraries, the following infrastructure will be needed:-

a) Computer Hardware: Server, P.C. with multimedia, U.P.S. Etc

b) Software: Any suitable software from GSDL, DSpace, etc which is interconnected and suitable for LAN and WAN connection.

c) Network: LAN, MAN, WAN, etc.

d) Printer: Laser printer, Dot matrix, Barcode printer, Digital graphic printer, etc.

e) Scanner: H.P. Scan jet, flatbed, Sheet feeder, Drum scanner, Slide scanner, Microfilming scanner, Digital camera, Barcode scanner etc

f) Storage Devices: Optical storage device, CD-ROM, juke box, etc. As in the digital environment it is reasonable to say that a central back up or archive should be created at the national level which will store information out put of the region as well as information from out side the country.

g) Other Audio Visual Aid: Color T.V., V.C.R., D.V.D., Sound box, Telephone, etc.

h) Humanware: Well trained manpower for online help.

      The use of search engines, Optical Character Recognition and metadata will allow digital library to operate.

5. Resources of a Digital Library: The resources of a digital library are those, which the computer can store, organize, transmit and display without any intervening conversion process. The resources of a digital library mainly consist of e-book, v-book, electronic tax, map, image, sound, and video. The digital material may be of multimedia types or any other i.e. only digital audio, video, full text information, photograph, drawing, digitized sound, 3D representation, etc. The collection may include structured /unstructured text, scanned images, graphic audios, video recording, etc. In the digital environment any one who has access to the internet can be a publisher by merely posting messages to an online discussion group or other, so digital libraries collection should also be enhanced with links to such resources.

a) On line Resources: Local database of traditional books in machine-readable form, E-book, v-book, electronic tax, map, image, sound, video, and multimedia, E-journal, etc.

b) Off line Resources: C.D-ROM, Juke Box, etc.

6. Advantages of the Digital Library: A digital library is not confined to a particular location or so called building, it is virtually distributed all over the world. The user can get his/ her information on his own computer screen by using the internet. Actually it is a network of multimedia system which provides finger tip access. The spoken words or the graphical display of a digital library is again having a different impact from the words that are printed. In the new environment owning a document will not be problem for the library because the user will pay for its uses.

a) No Physical Boundary: The user of a digital library need not go to the library physically; people from all over the world could gain access to the same information, as long as an Internet connection is available.

b) Round the Clock Availability: Digital libraries can be accessed at any time, 24 hours a day and 365 days of the year

c) Multiple Accesses: The same resources can be used at the same time by a number of users.

d) Structured Approach:  Digital library provides 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.

e) Information Retrieval: The user is able to use any search term bellowing to the word or phrase of the entire collection. Digital library will provide very user friendly interfaces, giving clickable access to its resources.

f) Preservation and Conservation: An exact copy of the original can be made any number of times without any degradation in quality.

g) 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 the library had no space for extension digitization is the only solution.

h) Networking: A particular digital library can provide the link to any other resources of other digital library very easily. Thus a seamlessly integrated resource sharing can be achieved.

i) Cost: 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.

7. Disadvantages of the Digital Library: The computer viruses, lack of standardization for digitized information, quick degrading properties of digitized material, different display standard of digital product and its associated problem, health hazard nature of the radiation from monitor, etc. makes digital libraries at times a handicap.

a) Copyright:  Digitization violates the copy right law as the thought content of one author can be freely transferred by others without his acknowledgement. One difficulty to overcome for digital libraries is the way to distribute information. How does a digital library distribute information at will while protecting the copyright of the author?

b) Speed of Access: As more and more computer are connected to the internet its speed of access is reasonably decreasing. If new technology will not evolve to solve the problem then in near future internet will be full of error messages.

c) Initial Cost is High: The infrastructure cost of digital library i.e. the cost of hardware, software, leasing communication circuit is generally very high.

d) Band width: Digital library will need high bandwidth for transfer of multimedia resources but the band with is decreasing day by day.

e) Efficiency: With the much larger volume of digital information, finding the right material for a specific task becomes increasingly difficult.

f) Environment: 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.

g) Preservation:  Due to technological developments, a digital library can rapidly become out-of-date and its data may become inaccessible.

8. Role of Librarian in Digital Environment: Though the digital environment is built as a system which can be used by its ultimate end user directly from their desk top PC but the role of librarian cannot be overlooked. In digital environment also the librarian and information scientist will be needed for packaging and repackaging of information, for electronic publishing, for reference purpose, to advice the user about the strategy to identify relevant electronic sources, etc. Thus the librarian will be more or less a hypertext engineer. In the new environment it will be very difficult for the librarian to decide what should be organized; how to give citation; how to organize the collection; etc because the new environment will be really challenging one for the librarian to decide who the authors are, who the publishers are and who the users are?

9. Conclusion: Digital libraries are not going to replace the physical existence of document completely but no doubt to meet the present demand, to satisfy the non local user digitization must be introduced so that at least libraries becomes of hybrid nature. The initial cost of digitization is high but experiment shows that once digitization is introduced then the cost to manage this collection will be cheaper than that of any traditional library. Day by day the cost of digitization is also decreasing, the online publication is increasing, the need of users are shifting towards a different environment so it is needless to say that after one or two years all library will shift over to digital mode, if not fully at least to some extent. So it is the pick time to all library and informational science professional to gear them in building digital library and taking it as a challenge.

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 e-books, digital libraries are rapidly growing in popularity.