Xml annessi e connessi

Editor's Notes

• #6: The Standard Generalized Markup Language ( ISO 8879:1986 SGML ) is an ISO Standard metalanguage in which one can define markup languages for documents. SGML is a descendant of IBM 's Generalized Markup Language (GML), developed in the 1960s by Charles Goldfarb, Edward Mosher and Raymond Lorie (whose surname initials were used by Goldfarb to make up the term GML[1]). SGML provides an abstract syntax that can be implemented in many different concrete syntaxes. For instance, although it is the norm to use angle brackets as tag delimiters in an SGML document (per the reference concrete syntax defined in the standard), it is possible to use other characters instead, provided that a suitable concrete syntax is defined in the document's SGML declaration.[2] For example, an SGML interpreter could be programmed to parse GML markup. In GML, tags are bounded by a colon on the left and a full stop on the right; an e prefix denotes an end tag: :xmp.Hello, world:exmp..
• #7: Lo S tandard G eneralized M arkup L anguage ( SGML ), è uno standard per la descrizione logica dei documenti . Discende dal Generalized Markup Language della IBM . L'idea centrale dello standard è un tipo di marcatura generica chiamata "marcatura descrittiva" che definisce la struttura logica dei documenti. L'organizzazione di un documento non è espressa usando la codifica dei sistemi di scrittura, che è finalizzata alla presentazione grafica, ma sono evidenziate le parti in cui è strutturato il documento (ad esempio paragrafi, capitoli) insieme ad altre particolarità del testo (come note, tabelle, intestazioni). Sono stati creati a questo scopo programmi come Alml , cioè sistemi di composizione SGML. Utilizzo originale Una porzione dell' OED ( 1985 ) con la sintassi SGML evidenziata SGML fu inizialmente sviluppato per permettere lo scambio di documenti machine-readable (leggibili da un computer) in progetti governativi, legali e industriali, che devono rimanere leggibili per diverse decadi (un periodo di tempo molto lungo nell'ambito dell' informatica ). Inizialmente usato per pubblicazione di testo e basi di dati , una delle sue maggiori applicazioni fu la seconda edizione dell' Oxford English Dictionary (OED), che era ed è interamente formattato usando un linguaggio SGML. Generalized Markup Language ( GML ) is a set of macros that implement intent-based markup tags for the IBM text formatter , SCRIPT/VS . SCRIPT/VS is the main component of IBM's Document Composition Facility (DCF). A starter set of tags in GML is provided with the DCF product. GML was developed in the 1960s by Charles Goldfarb , Edward Mosher and Raymond Lorie (whose surname initials were used by Goldfarb to make up the term GML [1] ). GML simplifies the description of a document in terms of its format, organization structure, content parts and their relationship, and other properties. GML markup (or tags) describes such parts as chapters, important sections, and less important sections (by specifying heading levels), paragraphs, lists, tables, and so forth. GML frees document creators from specific document formatting concerns such as font specification, line spacing, and page layout required by SCRIPT/VS. Using GML, a document is marked up with tags that define what the text is, in terms of paragraphs , headers , lists , tables , and so forth. The document can then be automatically formatted for various devices simply by specifying a profile for the device. For example, it is possible to format a document for a laser printer or a line ( dot matrix ) printer or for a screen simply by specifying a profile for the device without changing the document itself. A later and more extensive set of tags is provided by IBM's BookMaster product. GML preceded and was one of the two sources that were used as the basis for the industry-developed Standard Generalized Markup Language (SGML), a set of rules for creating structured document description languages . The Extensible Markup Language (XML) was initially a streamlined and simplified development of SGML, but has outgrown its parent in terms of worldwide acceptance and support. Derivatives XML Main article: XML XML is a subset of SGML, designed so as to make the parser much easier to implement than a full SGML parser. A consequence of the ease of implementation is that XML, rather than SGML, is nowadays widely used for deriving document specifications. Contributing to this is also the fact that few SGML-aware programs existed when XML was created. The number of XML applications today is large. XML also has a lightweight internationalization . XML is used for general-purpose applications, such as the Semantic Web , XHTML , SVG , RSS , Atom , XML-RPC and SOAP .
• #8: http://www.w3c.org Un’organizzazione fondata nel 1994 da TIM BERNERS-LEE in collaborazione con MIT (USA), INRIA (Francia) e Keio University (Giappone) al fine di “sviluppare protocolli comuni per migliorare l’interoperabilità e guidare l’evoluzione del World Wide Web” Il W3C produce sia specificazioni di interoperabilità, sia codice d’esempio. Il W3C ha circa 450 organizzazioni membre, includendo università, enti di ricerca, produttori di hardware e software, società di telecomunicazione, fornitori di contenuti, corporation, e enti governativi. UniBo-CS è membro dal 1999. Esiste un’organizzazione sorella, IW3C2 ( International World Wide Web Conference Committee ) che organizza conferenze scientifiche ed altri eventi a livello locale e internazionale.
• #12: 2.8 Processing Instructions In HTML, comments are sometimes abused to support nonstandard extensions. For instance, the contents of the script element are sometimes enclosed in a comment to protect it from display by a nonscript-aware browser. The Apache web server parses comments in .shtml files to recognize server-side includes. Unfortunately, these documents may not survive being passed through various HTML editors and processors with their comments and associated semantics intact. Worse yet, it's possible for an innocent comment to be misconstrued as input to the application. XML provides the processing instruction as an alternative means of passing information to particular applications that may read the document. A processing instruction begins with <? and ends with ?>. Immediately following the <? is an XML name called the target , possibly the name of the application for which this processing instruction is intended or possibly just an identifier for this particular processing instruction. The rest of the processing instruction contains text in a format appropriate for the applications for which the instruction is intended. For example, in HTML, a robots META tag is used to tell search-engine and other robots whether and how they should index a page. The following processing instruction has been proposed as an equivalent for XML documents: <?robots index="yes" follow="no"?> The target of this processing instruction is robots. The syntax of this particular processing instruction is two pseudo-attributes, one named index and one named follow, whose values are either yes or no. The semantics of this particular processing instruction are that if the index attribute has the value yes, then search-engine robots should index this page. If index has the value no, then robots should not index the page. Similarly, if follow has the value yes, then links from this document will be followed; if it has the value no, they won't be. Other processing instructions may have totally different syntaxes and semantics. For instance, processing instructions can contain an effectively unlimited amount of text. PHP includes large programs in processing instructions. For example: <?php mysql_connect("database.unc.edu", "clerk", "password"); $result = mysql("HR", "SELECT LastName, FirstName FROM Employees ORDER BY LastName, FirstName"); $i = 0; while ($i < mysql_numrows ($result)) { $fields = mysql_fetch_row($result); echo "<person>$fields[1] $fields[0] </person>\\r\\n"; $i++; } mysql_close( ); ?> Processing instructions are markup, but they're not elements. Consequently, like comments, processing instructions may appear anywhere in an XML document outside of a tag, including before or after the root element. The most common processing instruction, xml-stylesheet, is used to attach stylesheets to documents. It always appears before the root element, as Example 2-6 demonstrates. In this example, the xml-stylesheet processing instruction tells browsers to apply the CSS stylesheet person.css to this document before showing it to the reader. Example 2-6. An XML document with a processing instruction in its prolog <?xml-stylesheet href="person.css" type="text/css"?> <person> Alan Turing </person> The processing instruction names xml, XML, XmL, etc., in any combination of case, are forbidden in order to avoid confusion with the XML declaration. Otherwise, you're free to pick any legal XML name for your processing instructions.
• #20: http://www.w3.org/TR/2004/REC-xml11-20040204/#NT-ExternalID Standard DTDs may actually be stored at multiple URLs. For example, if you're drawing an SVG picture on your laptop at the beach, you probably want to validate the drawing without opening a network connection to the W3C's web site where the official SVG DTD resides. Such DTDs may be associated with public IDs. The name of the public ID uniquely identifies the XML application in use. At the same time, a backup URL is also included in case the validator does not recognize the public ID. To indicate that you're specifying a public ID, use the keyword PUBLIC in place of SYSTEM. For example, this document type declaration refers to the Rich Site Summary DTD standardized by Netscape: <!DOCTYPE rss PUBLIC "-//Netscape Communications//DTD RSS 0.91//EN" "http://my.netscape.com/publish/formats/rss-0.91.dtd"> A local catalog server can convert the public IDs into the most appropriate URLs for the local environment. The catalogs themselves can be written in XML, specifically the OASIS XML catalog format ( http://www.oasis-open.org/ committees / entity / spec.html ). In practice, however, PUBLIC IDs aren't used very much. Most of the time, validators rely on the URL to actually validate the document. If that is true then why have a PUBLIC identifier at all ? What is their purpose beware that you are skirting on the edge of a very deep "debate":-) Basically the public identifier gives a unique canonical name for the dtd that you can recognise; whereas the SYSTEM identifier may well point at a local path on the original author's system that doesn't make sense on yours. An XML parser may use either (or both) identifiers to find the file. So if you have an xml parser that has an xml catalogue of some sort that recognises say XHTML or Docbokk PUBLIC identifier, the file will work even if the system ID points at a file not accessable to you as your parser can use the catalogue to map the public ID to a local copy. Conversely if you don't have that public id in your catalogue (or if there is no public id) then you can perhaps find the file directly by using the system id. When the syntax was invented, for sgml, this last step would most likely fail as it would be a local file name so it would assume that you had local files in the same position. In XML when the SYSTEM is supposed to be a URI and so perhaps usable from anywhere in the world there is an argument (that I don't personally hold, but which is not unreasonable, and comes up often) that the SYSTEM ID is all you need and PUBLIC IDs no longer serve a purpose.
• #30: http://www.w3.org/TR/REC-xml-names/
• #38: Questa è la cosa che tra più in inganno chi scrive software, infatti il programma va quasi sempre e ogni tanto “si rompe”, come mai? La ragione sta nel fatto che sia ISO-8859-1(5) che UTF-8 usano la stessa rappresentazione binaria per i caratteri ASCII (è una scelta voluta per ragioni di efficienza e compatibilità) per cui non c’è differenza fra l’encoding in UTF-8 e ISO-8859-1 per i caratteri più comunemente utilizzati. http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info
• #39: http://www.w3.org/TR/REC-xml/#sec-guessing-no-ext-info Since ASCII is almost never an appropriate character set for an XML document, application/xml is much preferred over text/xml. Unfortunately, most web servers including Apache 2.0.36 and earlier are configured to use text/xml by default. If you're running such a version you should probably upgrade before serving XML files. [1] Therefore, an XML parser will attempt to guess the character set based on the first several bytes of the document. The main checks the parser makes include the following: If the first two bytes of the document are #xFEFF, then the parser recognizes the bytes as the Unicode byte-order mark. It then guesses that the document is written in the big-endian, UTF-16 encoding of Unicode. With that knowledge, it can read the rest of the document. If the first two bytes of the document are #xFFFE, then the parser recognizes the little-endian form of the Unicode byte-order mark. It now knows that the document is written in the little-endian, UTF-16 encoding of Unicode, and with that knowledge it can read the rest of the document. If the first four bytes of the document are #x3C3F786D, that is, the ASCII characters <?xm, then it guesses that the file is written in a superset of ASCII. In particular, it assumes that the file is written in the UTF-8 encoding of Unicode. Even if it's wrong, this information is sufficient to continue reading the document through the encoding declaration and find out what the character set really is.
• #40: Even if metadata is not available, the encoding declaration can be omitted if the document is written in either the UTF-8 or UTF-16 encodings of Unicode. UTF-8 is a strict superset of ASCII, so ASCII files can be legal XML documents without an encoding declaration. Note, however, that this only applies to genuine, pure 7-bit ASCII files. It does not include the extended ASCII character sets that some editors produce with characters like ©, ç, or ". Even if character set metadata is available, many parsers ignore it. Thus, we highly recommend including an encoding declaration in all your XML documents that are not written in UTF-8 or UTF-16. It certainly never hurts to do so.