View source for Viewdata

{{short description|Information retrieval service and legacy system}}
{{Infobox online service
| name                         = Viewdata
| title                        = Viewdata
| logo                         = 
| logo_size                    = 
| logo_alt                     =
| logo caption                 = 
| image                        = File:viewdata Graphics 1.jpg
| image_size                   = 200px
| image_alt                    =
| caption                      = Viewdata Graphics used in the experimental phone directory of [[Post Office Telecommunications]] in 1977. <br />The image is a graphical representation of the Post Office/[[British Telecom]] Research laboratories ([[Adastral Park]]) in [[Suffolk]], England.  Note the "_ to continue" rather than the correct "⌗ to continue", showing a common rendering error.
| developer                    = [[Samuel Fedida]], [[General Post Office|Post Office]]
| generation                   =
| type                         = [[Videotex]]
| launched                     = {{Start date and age|1974}} 
| discontinued                 = 
| version                      =
| version release date         =
| preview version              =
| preview version release date =
| updated                      =
| platform                     = Viewdata
| operating system             =
| status                       = 
| members                      = 
| website                      =
}}

[[File:Teletext Viewdata Terminal.png|thumb|right|300px|A Viewdata machine displayed in [[teletext]] format]]

'''Viewdata''' is a [[Videotex]] implementation.  It is a type of [[information retrieval]] service in which a [[subscriber]] can [[Access control|access]] a remote [[database]] via a [[common carrier]] [[Communication channel|channel]], request [[data]] and receive requested data on a [[video]] display over a separate channel. [[Samuel Fedida]], who had the idea for Viewdata in 1968, was credited as inventor of the system which was developed while working for the British [[General Post Office|Post Office]] which was the operator of the national telephone system. The first prototype became operational in 1974. The access, request and reception are usually via common carrier broadcast channels.  This is in contrast with [[teletext]].

== Design ==

Viewdata offered a display of 40×24 characters, based on [[ISO 646]] (IRV IA5) – 7 bits with no accented characters.<ref name=aei>{{cite web| url=http://aei.pitt.edu/94572/1/videotex.pdf | title=Proceedings of the Videotex in Europe | access-date=2023-12-26 | date=1979-07-19}}</ref>
Originally, Viewdata was accessed with a special purpose [[Computer terminal|terminal]] (or [[Emulator|emulation software]]) and a [[modem]] running at [[ITU-T]] [[ITU-T V.23|V.23]] speed (1,200 bit/s down, 75 bit/s up).<ref name=aei/> By 2004, it was normally accessed over [[TCP/IP]] using Viewdata [[client software]] on a [[personal computer]] running [[Microsoft Windows]], or using a Web-based emulator.

{{Infobox symbol
|name= Viewdata keypad symbols
|mark=⌗ ⚹
|unicode={{unichar|2317||html=}}<br /> {{unichar|26B9|html=|nlink=}}
|see also= 
|different from={{unichar|002A|html= | nlink= }}<br />{{unichar|0023|html= | nlink=}}
}}
[[File:Detail-Tastatur-FeTAp-751-1982.JPG |thumb|left|Detail of a telephone keypad displaying the sextile and Viewdata square]]
[[File:AVAYA 9611G IP Phone detail of star and hash.jpg |thumb|left|Detail of a more recent telephone keypad, in which (typographic) asterisk and number{{nbsp}}sign have replaced the ITU star and square]]

Viewdata uses special symbols already widely available on telephone keypads: the {{key press|⚹}} "star" key and the {{key press|⌗}} "square" key, as formally standardised by the [[International Telecommunication Union]].<ref>{{cite web | url =  http://www.itu.int/rec/T-REC-E.161-200102-I/en | title = E.161 : Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network | publisher = [[International Telecommunication Union]] | date= 2 February 2001 | access-date =  23 December 2019}}</ref> These are often treated as approximately corresponding to the ASCII [[asterisk]] (*) and [[number sign]] (#), which do not necessarily conform to the ITU specifications for the keypad symbols; the asterisk is also usually displayed smaller and raised.<ref name="L213105r" />

These symbols appear as 'Sextile' and 'Viewdata square' in the [[Miscellaneous Symbols]] and [[Miscellaneous Technical]] Unicode blocks, respectively. The sextile was added due to [[Astrological aspect|its use in astrology]],<ref name="L213105r">{{cite web|url=https://unicode.org/L2/L2013/13105r-telephony.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://unicode.org/L2/L2013/13105r-telephony.pdf |archive-date=2022-10-09 |url-status=live | title= Proposal to incorporate two telephony symbols into Unicode by glyph and annotation changes | date= 28 October 2013 | access-date =  23 December 2019 | author = Karl Pentzlin |id=UTC L2/13-105R}}</ref> and the square had previously appeared in the [[ISO/IEC 646#Variant comparison chart|BS_Viewdata]] character set, as a replacement for the underscore.<ref name="ISO-IR-047">{{cite iso-ir |title=Alphanumerics for viewdata and broadcast teletext |sponsor=BSI |sponsor-link=BSI Group |date=1981-06-01 |number=47}}</ref>

In 2013, the German national body submitted a [[Unicode Consortium|Unicode Technical Committee]] proposal to align the Unicode reference glyphs with the ITU specifications for these symbols, and annotate them as telephone keypad symbols on the code charts.<ref name="L213105r" /> {{as of|2019}} (Unicode 12.1), these changes have not been accepted/implemented.<ref>{{cite web |url=https://www.unicode.org/charts/PDF/U2300.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.unicode.org/charts/PDF/U2300.pdf |archive-date=2022-10-09 |url-status=live |title=Miscellaneous Technical |work=The Unicode Standard |author=Unicode Consortium |author-link=Unicode Consortium}}</ref>

== Uses ==

=== Travel industry ===
As of 2015, Viewdata was still in use in the [[United Kingdom]], mainly by the [[travel industry]]. [[Travel agent]]s use it to look up the price and availability of [[package holiday]]s and [[Commercial aviation|flight]]s. Once they find what the customer is looking for they can place a booking.

There are a number of factors still holding up a move to a [[World Wide Web|Web]]-based standard. Viewdata is regarded within the industry as low-cost and reliable, travel consultants have been trained to use Viewdata and would need training to book holidays on the Internet, and [[tour operator]]s cannot agree on a Web-based standard. 
{{Citation needed|date=December 2009}}

=== Bulletin board systems ===
{{Unreferenced section|date=June 2023}}

A number of Viewdata [[bulletin board system]]s existed in the 1980s, predominantly in the UK due to the proliferation of the [[BBC Micro]], and a short-lived ''Viewdata Revival'' appeared in the late 1990s fuelled by the [[retrocomputing]] vogue. Some Viewdata boards still exist, with accessibility in the form of [[Java (Sun)|Java]] [[Telnet]] clients.

== See also ==

* [[Prestel]]

== References ==

{{refs}}

== External links ==

* [http://www.its.bldrdoc.gov/fs-1037/dir-039/_5795.htm Definition at The Institute for Telecommunication Sciences]
* [http://www.viewdata.org.uk/ Celebrating the Viewdata Revolution] Including several Prestel Brochures
* [https://vd-view.azurewebsites.net/ vd-view] A Viewtex web client for TeeFax, Telstar, CCl4 and NXTel
* [https://github.com/simonlaszcz/vidtex vidtex] An ncurses/terminal client for TeeFax, Telstar, CCl4, NXTel and others
* {{FS1037C}}

{{Videotex}}

[[Category:Computer network technology]]
[[Category:History of computing in the United Kingdom]]
[[Category:History of telecommunications in the United Kingdom]]
[[Category:Legacy systems]]
[[Category:Videotex]]