- From: tomerm via GitHub <sysbot+gh@w3.org>
- Date: Sun, 10 Apr 2016 18:10:53 +0000
- To: public-i18n-archive@w3.org
Some introduction materials on Bidi layout (aka Bidi format if you wish). Bidirectional text can be stored in several formats (a.k.a. "layouts"), depending on the platform and the intended use. When bidi data is available but not in the appropriate layout, it is possible to convert it to the required layout by performing a "bidi transformation". On most platforms, there exist libraries of tools (often called "bidi engines") to execute bidi transformations. Bidi text can be stored in a variety of layouts characterized by a combination of 5 attributes: - ordering scheme - base direction - symmetric swapping - text shaping (for Arabic) - numeric shaping (for Arabic) Historically, data stored on mainframes (zSeries and iSeries) was in "visual" layout, i.e. according to a visual ordering scheme, ready for presentation on "dumb" devices like terminals or printers. With the advent of processing power closer to end users, as is the case for workstations and personal computers, it became common to store data in a newer "logical" layout. Currently, data in visual layout are still preponderant on zSeries and iSeries, while in Windows systems most data are created and processed in logical layout. Systems running Unix or its variants can handle data in either logical or visual layout, probably with some more affinity for the logical layout. Java GUI components expect bidi textual data to be in logical layout. bidi text within HTML may be in either logical or visual layout, but it is generally more convenient to format the data in logical layout, and browsers' support for data in logical layout is also better. As we have seen, bidi textual data can be stored according to various layouts. Visual layouts can be used straightforwardly for presentation, while logical layouts are more appropriate for most forms of processing. What happens if some data need processing, but are currently accessible in a visual layout? They must be converted to a logical layout. This operation is not trivial. It entails reversing parts of the text, but not all of it. It entails replacing some occurrences of symmetric symbols by their symmetric match. For Arabic, it also entails choosing the proper shape for each letter and the proper digits for each number. Fortunately, software tools already exist to accomplish such conversions. In general, the operation which converts a piece of bidi text from a source layout to a target layout is called a "bidi transformation". This can include going from a logical layout to a visual layout, or going the opposite way. The transformation may even leave the ordering scheme unchanged, but alter some or all of the other bidi attributes. -- GitHub Notification of comment by tomerm Please view or discuss this issue at https://github.com/w3c/charmod-norm/issues/80#issuecomment-208034480 using your GitHub account
Received on Sunday, 10 April 2016 18:10:55 UTC