World-Wide Web: The Information Universe
Contents
1. Phone Joe oe Group Joe in phone book Joe Bloggs 3 Joe Doe Group Sara Joe resources Joe Bloggs Joe Bloggs YD group 3 Main Street 4 202 676 7687 Encyclopaedia Cf N Y Link p Search The W3 model involves hypertext links and index searches The reader starts at the home page 1 and quickly uses his own links group wide or public links to find resources Indexes such as the phone book 2 are represented as documents with the possibility of inputting search words The result is a virtual hypertext document 3 which points to the documents found 4 Fig 1 A web of links and indexes Features to note are e Information need only be represented once as a reference may be made instead of making a copy e Links allow the topology of the information to evolve so modeling the state of human knowledge at any time without constraint e The web stretches seamlessly from small personal notes on the local workstation to large databases on other continents e Indexes are documents and so may themselves be found by searches and or following links An index is represented to the user by a cover page which describes the data indexed and the properties of the search engine e The documents in the web do not have to exist as files they can be virtual documents generated by a server in response to a que2. Fig 3 A schmatic illustration of the encoding of hypertext data The link is represented in the winodw by underlining on the terminal by a reference number The current WAIS model requires that the results of a search point to documents available from the same server That is the same server is responsible for indexing and actually providing the data In the W3 world this restriction does not exist A practical advantage with this approach is that as Yeong points out 13 a large multimedia document may be most efficiently retrieved from a different host and using a different protocol to that used for the original query Futhermore as on line information proliferates an important function is that of third party reviewers indexers and overview writers who refer to data they do not actually hold It is expected that these services will be a key to the control of the information explosion and a valuable asset to the community A W3 user builds a personalized web of information by making links from his own notebook into the web He can make a link to the result of performing a search such that next time he follows the link the search is reevaluated This is the equivalent of storing a WAIS question there is a good mapping between the models The W clients do not currently support relevance feedback although it is not alien to the model There are two occasions when hypertext would particularly enhance the WAIS model Firstl
3. soon be out of date The Future The success of the pilot project prompted further development of W compliant software and information Current client projects within various organizations include three X11 based browsers and a Macintosh browser Various server gateways to other information systems have been produced and the total amount of information available on the web is becoming very significant especially as it includes all anonymous FTP archives WAIS servers and Gopher servers as well as specific W3 servers We notice that the functions of each of these servers could be provided by a W3 server and so look forward to a single protocol 1 2 3 4 5 6 7 8 9 10 11 12 13 which can be used by the whole community The Archie project 15 provides an index into the internet archives and is an excellent example of a service which we hope to make available in the web We can imagine such indexing being extended to cover other forms of data W3 provides a basic infrastructure for information access All kinds of indexing searching filtering and analysis tools could usefully be built using the generic w3 access mechnaism and so be applied to all the various domains of data Their results could then be made available on the web Many possible research projects in hypertext are enabled by the existence of a very large linked information base Meanwhile the W3 team at CERN and collaborators worldwid
4. World Wide Web The Information Universe Tim Berners Lee Robert Cailliau Jean Francois Groff Bernd Pollermann CERN 1211 Geneva 23 Switzerland Abstract The World Wide Web W3 initiative is a practical project to bring a global information universe into existence using available technology This article describes the aims data model and protocols needed to implement the web and compares them with various contemporary systems The Dream Pick up your pen mouse or favorite pointing device and press it on a reference in this document perhaps to the author s name or organization or some related work Suppose you are directly presented with the background material other papers the author s coordinates the organization s address and its entire telephone directory Suppose each of these documents has the same property of being linked to other original documents all over the world You would have at your fingertips all you need to know about electronic publishing high energy physics or for that matter Asian culture If you are reading this article on paper you can only dream but read on Since Vannevar Bush s article 1 men have dreamed of extending their intellect by making their collective knowledge available to each individual by using machines Computers give us two practical techniques for the man knowledge interface One is hypertext in which links between pieces of text or other media mimic human associatio
5. e invite any information suppliers to join the web contributing information or software Detailed information about W3 protocols and data formats etc is available from our W server The crudest way to access this is by telnet to info cern ch A better way is to run browser software available by anonymous FTP from the same host on your local machine If you use a window oriented browser then you will be able to read articles like this on your screen When you do pick up your pen mouse or favorite pointing device and press it on a reference in this document the dream is coming true REFERENCES Bush Vannevar As We May Think The Atlantic Monthly July 1945 Nelson Theodor H Literary Machines version 90 1 Mindfull press 1990 Beyond Hypertext The DECWindows Hyperenvironment Vision Digital Equipment Corporation Maynard MA 1990 Kahn Paul and Normal Meyrowitz Guide HyperCard and Intermedia A Comparison of Hypertext Hypermedia Systems IRIS Technical Report 88 7 Brown University Providence RI 1988 Cate Vincent Carnegie Mellon Univerity private communication Alberti et al Notes on the Internet Gopher Protocol Univeristy of Minnesota December 1991 Neuman Clifford B The Prospero File System User s manual Department of Computer Science and Engineering University of Washington Kahle B et al WAIS Interface Prototype Functional Specification Thinking Machines Corporat
6. ion April 1990 Postel J and Reynolds J File Transfer Protocol FTP Internet RFC 959 October 1985 Kantor B and Lapsley P A proposed standard for the stream based transmission of news Internet RFC 977 February 1986 Halasz F amp Schwartz M The Dexter Hypertext reference Model Proceedings of the Hypertext Standardization Workshop January 16 18 1990 National Institute of Standards and Technology GoldFarb Charles F Information Technology Hypermedia Time based Structuring Language HyTime ISO IEC CD 10744 Draft Yeong W Towards Networked Information Retrieval Technical report 91 06 25 01 Performance Systems International Inc 14 Yeong W P S I Representing Public Archives in the Directory Internet Draft 15 November 1991 Emtage A and Deutch P archie and Electronic Directory Service for the Internet to be presented to the 1992 usenix conference
7. mation bus pays off as more clients and servers are plugged in and universal readership is achieved Writing a server for new data is generally a simple task because it requires no human interface programming Document Naming The fulcrum on which the document universe rests is the scheme for naming documents A document name provides a method for the client to find the server and for the server to find the document In the W3 model a name can also specify a part of the document to be selected by the displaying application Although a document name is normally hidden in the hypertext syntax transferred over the link in practice it must sometimes be referred to by people and passed through applications such as mail which are not yet hypertext aware It must therefore ideally be composed of printable characters and manageably short Any lasting reference to a document must be a logical name rather than a physical address That is it should refer to a document s registration with some publishing organization rather than any physical location so that its location may later be moved The client is therefore prepared to follow several stages of translation by name servers before finding a final document server Similarly a document name should not contain any information which is transitory such as the particular formats available for a document or its length for example The W naming scheme fulfills these requirements but i
8. mple Gopher protocol and therefore allows links into the Gopher system The easy start up of these systems has made them fairly popular It is true that a menu is necessarily a more restricting medium of communication than general hypertext a page of hypertext can convey more information to the reader about the choices to be followed by using more flexible formatting Hypertext allows menus of links to lead to nodes with progressively greater textual content However the restricted world of plain text and menus with its ease of publication is adequate for many information providers Similarly W3 clients also have built in ability to browse the world of anonymous FTP archives and a gateway provides access to Digital s VMS Help information X 500 and the Web The x 500 standard for name servers provides a useful tool for long term naming of documents Initially intended for coordinates of people and organizations to be used for documents it needs extensions similar to though simpler than those proposed for example by Yeong 14 The chief attribute of a document for W3 purposes is the W physical address Once access to x 500 name servers is widely available User Friendly Names will form an appropriate W3 document name format for logical addresses Experience with the w3 pilot project The first client software written to the W3 requirements ran on the NeXT machine using the NeXTStep graphic user interface tools Thi
9. n of ideas The other is text retrieval which allows associations to be deduced from the content of text In the first case the reader s operation is typically to click with a mouse or type in a reference number in the second case it is to supply some words representing that which he desires The W ideal world allows both operations and provides access from any browsing platform Reality Existing research projects and commercial products are not far from achieving parts of this dream The Xanadu system 2 is an ambitious distributed hypertext project Existing hypertext systems see for example 3 4 tend to be restricted to the local or distributed file system and often are developed with a limited set of platforms in mind Contemporary information retrieval and access systems such as Alex 5 Gopher 6 Prospero 7 and WAIS 8 cover a wide area without the hypertext functionality Merging the techniques of hypertext information retrieval and wide area networking produces the W3 model This poses specific requirements on document naming schemes protocols and data representation The W3 data model The W model uses both paradigms of hypertext link and text search in a complementary fashion as neither can replace the functionality of the other Figure 1 shows how a personalized web of information is built from these operators My home page oea The phone book 2
10. ry or document name They can therefore represent views of databases or snapshots of changing data such as the weather forecast financial information etc A pleasing and useful aspect is that almost all existing information systems can be represented in terms of the W3 model A menu becomes a page of hypertext with each element linked to a different destination The same is true of a directory whether part of a hierarchical or cross linked system The notion of many named indexes within the web allows a given search engine and database to be visible with several different addresses each representing different options for the search algorithm For example the index library books titau substring may give a title and author search whereas Library books text exact may give an exact word full text search Addresses are discussed in more detail below Publishing From the information provider s point of view existing information systems may be published as part of the web simply by giving access to the data through a small server program The data itself and the software and human procedures which manage it are left entirely in place This approach has allowed for example a mainframe based document storage and index system to be opened up to access from all platforms in the organization To see how this is done requires a brief overview of the W architecture W3 Architecture Hypertext and text retrieval systems have been a
11. s hypertext browser editor demonstrated the ease of use of a window based hypertext interface to global information It also allowed an overview hypertext database to be built to point to data on the web by subject or organization The second client written was a line mode browser for character mode terminals Being portable to almost any machine it assures universal readability of all published documents Hypertext documentation was put on line and gateways were set up into various existing information systems Enthusiastic users of the browsing software particularly appreciated the consistent user interface for all types of data Reading news articles as hypertext was a good example the same user interface is provided and references between articles and between articles and the news groups in which they are published are all consistently represented as links It became evident that both hypertext links and text search are important parts of the model A typical information hunt will start from a default hypertext page by following links to an index A search of that index may return the required data or some more links may be followed Sometimes a further index may be found and that searched and so on When the user of a hypertext editor has found what he wants no matter how remote he can make a new link to it from his home page so that he can find it again later almost instantly This is generally preferable to making a copy which may
12. s otherwise open to the addition of new protocols as technology evolves For this purpose a prefix is used to identify the protocol and therefore naming scheme to be used Clients which do not have that protocol in their repertoire refer to a gateway for translation Protocols The W clients are built on a common core of networking code for information access This core provides access using widely deployed internet protocols such as e File Transfer Protocol FTP 9 e Network News Transfer Protocol NNTP 10 e Access to mounted file systems A new search and retrieve protocol was found necessary known as HTTP Faster than FTP for document retrieval this also allows index search HTTP is similar in implementation to the internet protocols above and similar in functionality to the WAIS protocol Some differences are discussed below Document Formats The Dexter data model of hypertext 11 provided a conceptual model for hypertext systems and the HyTime standard 12 formalizes hypertext at a high level The W project defines a concrete syntax in the SGML style for basic hypertext as used for menus search results and on line hypertext documentation Every W browsing application is able to parse this simple format see Fig 3 In the pilot phase of the project this format was all that was required but in the second phase format negotiation between client and server will allow the exchange of information in any medi
13. um using any mutually acceptable representation WAIS and the Web From the point of view of the W3 dream the WAIS protocol represents a significant advance on the search and retrieve SR protocol standard Z39 50 ISO 10163 by being stateless and introducing a persistent name The document names used are local to the containing database but these names may be appended to the database name and host address to form a universal W3 address In this way WAIS indexes and servers can be represented in the web A gateway program running at CERN and available for general use provides this mapping The WAIS model uses separate source files to describe indexes The WAIS W gateway keeps caches of these files using them to build descriptive cover pages for indexes LJ PFD Error codes E PFD Error Codes ERROR CODES J Error Codes Codes returned by the PED Codes returned by the PFD 1 program include program include e No paper in tray o No paper in tray No people in room o No people in room No data in file o No data in file 1 9 Return for more Help or Quit A Terminal client Window client TLE PFD Error Codes lt TITLE gt gt ErRor Codes lt H1 gt Sending hypertext data over the network in a high level logical representation allows optimum presentation according to the facilities of the reader s platform Original gt Data
14. vailable for many years and a valid question is why a global system has not already come into existence Traditional answers to this question are the lack of e A common naming scheme for documents e Common network access protocols e Common data formats for hypertext Most research in hypertext systems the Xanadu project excepted has focussed on the user interface and authoring questions rather than the questions of wide area and long term distribution These architectures have assumed that users share a common application program running on computers often of the same type which share a common file system The W3 architecture must cope with a widely distributed heterogeneous set of computers running different applications which use different preferred data formats This requires a client server model The client has the responsibility for resolving a document address into a document using its repertoire of network protocols The server provides data in a simple hypertext or plain text form or by negotiation with the client in any other data format dumb PC Mac Addressing scheme Common Protocol Format Negotiation Gateways Network News Fig 2 The W architecture in outline Existing data It may be more difficult initially to develop a generic hypertext browser than a specific front end for a particular information system However the de coupling of the client and server programs by the infor
15. y users often would like to be able to browse through available WAIS indexes WAIS and W3 both regard indexes as documents and therefore allow them to be found using the same techniques as for documents In fact the WAIS W gateway allows a W3 hypertext overview to be made with pointers to WAIS indexes Secondly when one has found a piece of text WAIS delivers just that part of a file which has been found Very often one would like links to surrounding information in the same database The popularity of WAIS has been a great boost to the world of online information Its integration with universal naming and hypertext is to be greatly encouraged Menu systems and The Web The Alex 5 Internet Gopher 6 and Prospero 7 systems each use the directory and file or menu and document model to implement a global information system These map into the web very naturally as each directory menu is represented by a list of text elements linked to other directories or files documents These systems are very comfortable for readers who are used to hierarchical file systems for whom directories are an established concept Even when the structure is in fact cross linked the reader feels at home as he regards it as a tree structure Furthermore for the information provider such systems are easy to build by cross linking existing file systems An example of mapping a menu system onto the web is made by the W client software which incorporates the si
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