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what two other terms are used to refer to “empirical validity”?

Character encodings for beginners

Intended audition: content authors, users, and anyone who is unsure about what a character encoding is, and wants a brief summary of how information technology affects them.

Question

What is a character encoding, and why should I intendance?

Answer

First, why should I care?

If you lot utilize anything other than the most basic English text, people may non be able to read the content you create unless you say what grapheme encoding you used.

For example, y'all may intend the text to look like this:

mojibake1.gif

but it may actually display like this:

mojibake2.gif

Not only does lack of character encoding data spoil the readability of displayed text, but it may mean that your data cannot be found by a search engine, or reliably processed by machines in a number of other ways.

And so what'due south a graphic symbol encoding?

Words and sentences in text are created from characters. Examples of characters include the Latin letter á or the Chinese ideograph 請 or the Devanagari character ह.

Characters that are needed for a specific purpose are grouped into a graphic symbol ready (also called a repertoire). (To refer to characters in an unambiguous way, each character is associated with a number, chosen a code indicate.)

The characters are stored in the computer equally one or more bytes.

Basically, y'all tin visualise this past assuming that all characters are stored in computers using a special lawmaking, like the ciphers used in espionage. A grapheme encoding provides a primal to unlock (ie. scissure) the code. It is a prepare of mappings betwixt the bytes in the figurer and the characters in the character gear up. Without the key, the data looks like garbage.

So, when you input text using a keyboard or in some other way, the character encoding maps characters you lot choose to specific bytes in computer memory, and then to display the text it reads the bytes dorsum into characters.

Unfortunately, at that place are many different character sets and character encodings, ie. many different means of mapping betwixt bytes, code points and characters. The section Boosted information provides a little more particular for those who are interested.

Nearly of the time, nonetheless, you lot will not demand to know the details. You volition just need to exist certain that you lot consider the advice in the section How does this touch on me? below.

How do fonts fit into this?

A font is a drove of glyph definitions, ie. definitions of the shapes used to brandish characters.

Once your browser or app has worked out what characters information technology is dealing with, it will then await in the font for glyphs information technology can utilize to display or impress those characters. (Of course, if the encoding information was incorrect, information technology will be looking up glyphs for the wrong characters.)

A given font volition commonly cover a single character set up, or in the case of a large character prepare like Unicode, merely a subset of all the characters in the prepare. If your font doesn't have a glyph for a particular character, some browsers or software applications will wait for the missing glyphs in other fonts on your system (which volition mean that the glyph will await different from the surrounding text, similar a ransom note). Otherwise you will typically see a square box, a question marking or some other character instead. For example:

mojibake3.gif

How does this affect me?

Every bit a content author or developer, you lot should nowadays always choose the UTF-8 graphic symbol encoding for your content or data. This Unicode encoding is a adept selection because you lot can use a unmarried character encoding to handle any grapheme you are likely to need. This greatly simplifies things. Using Unicode throughout your system also removes the need to track and catechumen betwixt various character encodings.

Content authors need to find out how to declare the character encoding used for the document format they are working with.

Note that just declaring a different encoding in your page won't alter the bytes; y'all demand to save the text in that encoding also.

Equally a content author, y'all need to check what encoding your editor or scripts are saving text in, and how to salve text in UTF-8. (Information technology's ordinarily the default these days.) You may also need to check that your server is serving documents with the right HTTP declarations.

Developers need to ensure that the various parts of the system can communicate with each other, sympathise which character encodings are beingness used, and support all the necessary encodings and characters. (Ideally, you would employ UTF-viii throughout, and be spared this problem.)

The links below provide some further reading on these topics.

Boosted data

This section provides a trivial boosted information on mapping between bytes, code points and characters for those who are interested. Experience free to just skip to the section Farther reading.

In the coded character set up called ISO 8859-1 (also known as Latin1) the decimal lawmaking point value for the alphabetic character é is 233. Notwithstanding, in ISO 8859-5, the same lawmaking point represents the Cyrillic character щ.

These character sets contain fewer than 256 characters and map code points to byte values directly, so a code betoken with the value 233 is represented past a unmarried byte with a value of 233. Notation that it is simply the context that determines whether that byte represents either é or щ.

There are other ways of handling characters from a range of scripts. For example, with the Unicode character prepare, y'all tin can represent both characters in the same set up. In fact, Unicode contains, in a single set, probably all the characters you lot are likely to always demand. While the letter é is still represented past the code point value 233, the Cyrillic graphic symbol щ at present has a code point value of 1097.

On the other manus, 1097 is as well big a number to exist represented by a single byte*. So, if you use the grapheme encoding for Unicode text called UTF-eight, щ will be represented past two bytes. However, the code betoken value is not simply derived from the value of the two bytes spliced together – some more than complicated decoding is needed.

Other Unicode characters map to 1, iii or iv bytes in the UTF-8 encoding.

Furthermore, note that the letter é is also represented by two bytes in UTF-8, not the unmarried byte used in ISO 8859-one. (Merely ASCII characters are encoded with a unmarried byte in UTF-8.)

UTF-8 is the near widely used fashion to represent Unicode text in spider web pages, and y'all should always use UTF-viii when creating your web pages and databases. But, in principle, UTF-eight is only one of the possible ways of encoding Unicode characters. In other words, a single lawmaking signal in the Unicode character set can actually be mapped to dissimilar byte sequences, depending on which encoding was used for the document. Unicode code points could be mapped to bytes using any one of the encodings chosen UTF-8, UTF-xvi or UTF-32. The Devanagari character क, with lawmaking indicate 2325 (which is 915 in hexadecimal annotation), volition be represented by two bytes when using the UTF-16 encoding (09 15), iii bytes with UTF-eight (E0 A4 95), or four bytes with UTF-32 (00 00 09 15).

There tin exist further complications beyond those described in this department (such as byte order and escape sequences), simply the detail described here shows why it is of import that the application yous are working with knows which character encoding is advisable for your data, and knows how to handle that encoding.

The article Character encodings: Essential concepts provides some gentle introductions to related topics, such as Unicode, UTF-8, Graphic symbol sets, coded graphic symbol sets, and encodings, the document grapheme set, graphic symbol escapes and the HTTP header.

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Source: https://www.w3.org/International/questions/qa-what-is-encoding