Idea Transcript
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Methods for access to databases through Internet Introduction
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Methods for access to databases through Internet A growing number of methods are available to provide (end-) users access to the contents of databases • through the international Internet or • through an institutional intranet
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Methods for access to databases through Internet Using telnet
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Using telnet: steps involved The end-user applies a client program that supports the telnet protocol to connect to a telnet server that provides access to some program on a server computer to retrieve data from the database.
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Using telnet: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ client client software software for for telnet telnet
telnet protocol
telnet telnet server server
retrieval retrieval software software
data base
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Using telnet: example Using the Windows 95 telnet client program
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Using telnet: comments (Part 1) • + Advantage: »Relatively cheap, old client workstations can be used; in other words, more expensive, recent and powerful workstations are not required.
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Using telnet: comments (Part 2) • - Disadvantages: »The user interface in telnet is character-based only, provides not some graphical user interface that most users prefer. »Starting the telnet client from the Netscape web browser requires some installation. »A telnet client provides only a general user interface. Besides this the database server has to provide additional components to the user interface for retrieval.
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Using telnet: comments (Part 3) • Using telnet is considered as obsolete by many, due to the popularity of the web-approach; telnet access is replaced by access through web browsers / clients. • Nevertheless, it is still applied.
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Methods for access to databases through Internet Using proprietary client software
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Using proprietary client software: steps involved The end-user applies not an open standard client program, but a proprietary client program that is specifically developed to retrieve data through the Internet from the database on a server computer. (Such a retrieval client program is developed in most cases by or for the distributor of the database.)
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Using proprietary client software: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ proprietary proprietary client client software software
Internet Internet server server
retrieval retrieval software software
data base
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Using proprietary client software: examples • SPIRS = client software for ERL, by SilverPlatter • Probase = client software for Data-Star
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Using proprietary client software: comments (Part 1) • + Advantages: »The proprietary client program for retrieval is designed specifically for the target databases, so that it can provide a more suitable user interface than a more general, standard client program. »Some metadata related to the specific databases on the server can reside on the client together with the client software, so that the end-user can access these offline, for instance to prepare a search action or to select a particular database from a set of databases that are accessible.
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Using proprietary client software: comments (Part 2) • - Disadvantages: »This approach requires installation, maintenance and learning of specific software on each client computer; that costs time and disk space. »Using a graphical interface as well as metadata on the client system requires a relatively powerful client workstation.
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Using proprietary client software: comments (Part 3) • This approach is obsolete due to the popularity of the web approach; it is more and more replaced by access through “universal”, general web clients.
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Methods for access to databases through Internet Using the web and a database server
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Using WWW and a database server: steps involved The end-user applies a general, “universal” web client program that supports by definition the hypertext transfer protocol (http) to connect to a web (http) server that provides access to some program on a server computer to retrieve data from the database.
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Using WWW and a database server: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ http client client protocol software software for for WWW WWW
WWW WWW http http server server
CGI or ...
retrieval retrieval software software
data base
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Using WWW and a database server: example
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Using WWW and a database server: comments (Part 1) • CGI = Common Gateway Interface = a standard • + Advantages: »Requires only common, well-known, “universal” WWW browser software on the client computers. »A graphical interface is possible with a graphical web client program.
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Using WWW and a database server: comments (Part 2) • - Disadvantages: »Using a graphical interface in the web client requires a relatively powerful client workstation. »A web client provides only a general user interface. Besides this the database server has to provide additional components to the user interface for retrieval. »Requires not only a web server, but also a database server.
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Using WWW and a database server: comments (Part 3) • An increasing number of classical, character-based commercial, public access database hosts offer access in this way: Examples: »Cambridge Scientific, Data-Star, Dialog, Ovid, SilverPlatter,…. • This approach is very common since the end of the 1990s.
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Using WWW and a database server: extensions • In more complicated systems, a »Java applet, or »script (JavaScript, VBScript,…) may be sent from the WWW server to the client computer to support further interactions between the client computer and the database server (even besides HTTP). • Example: access to databases distributed by Ovid and SilverPlatter
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Methods for access to databases through Internet Using Z39.50 protocol
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Using Z39.50 directly from the client computer: steps involved The end-user applies directly on the client workstation one of the available client programs that function according to the open protocol Z39.50, that is developed to retrieve data through the Internet from one Z39.50 compliant database server computers, or even from several Z39.50 compliant database server computers at the same time.
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Using Z39.50 directly from the client computer: scheme User User
Client Client computer computer ++ client client software software for for Z39.50 Z39.50
Internet Internetor oran anintranet intranet
Z39.50 protocol
11or orseveral several Z39.50 compliant Z39.50 compliant retrieval retrievalsoftware software servers servers (simultaneously) (simultaneously)
data base(s)
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Using Z39.50 directly from the client computer: comments (Part 1) • This approach is mainly used in some libraries for access to catalogues and other databases. • + Advantage: »More than one database can be accessed at the same time. This allows time savings when searching for rare records.
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Using Z39.50 directly from the client computer: comments • - Disadvantages: »Requires installation, maintenance, and learning of Z39.50 client software on the client computers; that costs time and disk space. »Not all databases can be accessed using the Z39.50 protocol. • The approach is not common, in spite of the sophistication and the suitability for retrieval purposes.
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Using Z39.50 through a WWW gateway: scheme User User Internet Internetor oran anintranet intranet Client Client WWW WWW computer computer server server ++ http (gateway) (gateway) client client protocol ++ software software Z39.50 Z39.50 for for client client WWW WWW
11or or Z39.50 several several protocol Z39.50 Z39.50 servers servers
data base(s)
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Using Z39.50 through a WWW gateway: comments • Applied to search the Library of Congress catalogue and many other bibliographic databases. • + Advantages: »Does not require installation, maintenance, and learning of Z39.50 client software on the client computers. »Requires only common, “universal” WWW browser software on the client computers. • Some WWW servers provide a gateway that offers access to more than one Z39.50 server and their databases at the same time.
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Using Z39.50 through a WWW gateway: example
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**--Example
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Using Z39.50 through a WWW gateway: example
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Using Z39.50 through a WWW gateway: example • The EEVL subject directory on the WWW that is specialised in engineering includes since 2005 EEVL Xtra, which allows simultaneous searching of open access databases in the field of engineering.
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Methods for access to databases through Internet Using Windows server software as terminal server
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Using ICA with database(s) on a Windows server: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ ICA client client protocol software software for for ICA ICA
Windows Windowsserver serversoftware software ++ICA server ICA server with with NOT-client-server NOT-client-server retrieval retrievalsoftware software
data base
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Using ICA with database(s) on a Windows server: comments • ICA = Intelligent Console Architecture network protocol • Back to the mainframe? • Not common
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Using ICA with database(s) on a Windows server: comments (2) • + Advantage: »Can be used for instance for in-house access to non-clientserver retrieval software and databases running on a Windows server (examples: Chemical Abstracts on CD-ROM,…). • -Disadvantages: »Requires a powerful server “to do the work” »Requires additional payment for terminal server software
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Using ICA with database(s) on a Windows server: advantages • + Advantages: »Less maintenance and control required of client-pc park in an organisation. »Minimal “thin” client hardware and software is sufficient to implement this system. »Can be used for instance for in-house access to non-clientserver retrieval software and databases running on a Windows server (examples: Chemical Abstracts on CD-ROM,…).
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Using ICA with database(s) on a Windows server: disadvantages • -Disadvantages: »Requires a powerful server “to do the work”. »Requires additional payment for terminal server software. »Requires additional expertise among personnel on the implementation and maintenance of this kind of terminal server systems. »Multimedia applications may not work as well as by using a more “thick” client.
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Methods for access to databases through Internet Using point and click interfaces
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Using “special” methods for Internet database access • Interactive atlases. Geographical Information Systems (GIS). • “Select, point and click” user interfaces to “databases”
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Using “special” methods: example
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Using “special” methods: atlas
Result of a “search”:
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Using “special” methods: example
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Methods for access to databases through Internet Using a priori export of a database to HTML pages
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Using a priori export of a database to HTML pages: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ http client client protocol software software for for WWW WWW
WWW WWW http httpserver server
a priori export of a database to one or several data base html pages
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Using a priori export of a database to HTML pages: advantages • +Advantages »Only a universal WWW browser is required at the client side. »Useful to access records from different databases merged together, through one interface at the same time. »A simple solution for small and simple databases.
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Using a priori export of a database to HTML pages: disadvantages • - Disadvantages: »The database is not searchable anymore = individual records cannot be retrieved. »The data in the HTML format is not always as up to date as the original database. »Not suitable for large and complicated databases. »Not suitable for transaction processing.
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Using a priori export of records to HTML pages: scheme User User Internet Internetor oran anintranet intranet Client Client computer computer ++ http client client protocol software software for for WWW WWW
WWW WWW http httpserver server ++ software software to toindex index HTML HTMLpages pages!!
a priori export of database records to html pages
data base
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Using a priori export of records to HTML pages: advantages • +Advantages »The database is still searchable = records can be retrieved. »Only a universal WWW browser is required at the client side. »Useful to access records from different databases merged together, through one interface at the same time. »HTML/WWW retrieval programs are familiar to many users.
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Using a priori export of records to HTML pages: disadvantages • - Disadvantages: »Each database record becomes an HTML page/file. »Consumes more disk space than the original database(s). »An HTML/WWW index and retrieval program is required (such as the package used by AltaVista).
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Methods for access to databases through Internet Using the protocol for metadata harvesting of the Open Archives Initiative
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Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) user user
Client computer + client software
Search & retrieval
Data Providers
Service Provider request
Metadata database server
http protocol
metadata
PMH metadata
http protocol
metadata
Digital objects
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!! Task - Assignment !!
Read: Read: Breeding, Breeding,Marshall Marshall Understanding Understandingthe theprotocol protocolfor formetadata metadataharvesting harvesting of the Open Archives Initiative. of the Open Archives Initiative. Computers Computersin inLibraries, Libraries,September September2002, 2002,pp. pp.24-29. 24-29.
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!! Task - Assignment !! Read: Read: Open OpenArchives ArchivesForum Forum OAI for Beginners OAI for Beginners --the theOpen OpenArchives ArchivesForum Forumonline onlinetutorial. tutorial.[online] [online] Available Availablefrom: from:http://www.oaforum.org/tutorial/ http://www.oaforum.org/tutorial/[cited [cited2004] 2004] 1. OAI for Beginners: Overview 1. OAI for Beginners: Overview 2.2.History Historyand anddevelopment developmentof ofOAI-PMH OAI-PMH
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?? Question ?? In Inthe thecase casethat thatdatabases databasesare areproduced produced where Internet bandwidth is where Internet bandwidth islow, low, then which approach is probably more then which approach is probably moreappropriate appropriate to provide simultaneous access to more than to provide simultaneous access to more thanone onedatabases: databases: Z39.50 or Z39.50 or Open OpenArchives ArchivesInitiative Initiative --protocol protocolfor formetadata metadataharvesting? harvesting? Why? Why?
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?? Question ?? Explain Explainadvantages advantagesand anddisadvantages disadvantages of ofthe theprotocols/methods protocols/methodsto toprovide provideaccess access to more than one database in one action to more than one database in one action:: Z39.50 Z39.50versus versus Open Archives Open ArchivesInitiative Initiative --protocol for metadata protocol for metadataharvesting? harvesting?
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