XML - Wikipedia, the free encyclopedia. In computing, Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human- readable and machine- readable. The W3. C's XML 1. Specification. Although the design of XML focuses on documents, the language is widely used for the representation of arbitrary data structures. XML- based formats became the default for many office- productivity tools, including Microsoft Office (Office Open XML), Open. This tutorial explains the use of Elements and Attributes within an XML Schema (XSD). Office. org and Libre. Office (Open. Document), and Apple's i. Work. XML has also provided the base language for communication protocols such as XMPP. Applications for the Microsoft. NET Framework use XML files for configuration. Apple has an implementation of a registry based on XML. IETFRFC 7. 30. 3 gives rules for the construction of Internet Media Types for use when sending XML. It also defines the media types application/xml and text/xml, which say only that the data is in XML, and nothing about its semantics. The use of text/xml has been criticized. This is not an exhaustive list of all the constructs that appear in XML; it provides an introduction to the key constructs most often encountered in day- to- day use. Character. An XML document is a string of characters. Almost every legal Unicode character may appear in an XML document. Processor and application. The processor analyzes the markup and passes structured information to an application. Altova XMLSpy 2016 Tutorial. Altova XMLSpy 2016 Enterprise Edition 1. Creating an XML Schema. You will learn how to create an XML Schema in XMLSpy's intuitive Schema View, how to create complex content models using drag-and. Itunes Xml Schema Pdf Tutorial For Beginners The Final Cut Pro X XML (FCPXML) format lets you import and export XML FCPXML describes certain aspects of projects and events that are useful. XML Schema Tutorial Source: W3Schools Schema Tutorial. XSD Tutorial for beginners - Learn XSD in simple and easy steps starting from Overview, Syntax, Validation, Simple Types, Complex Types, String, Date Time, Numeric, Miscellaneous. The specification places requirements on what an XML processor must do and not do, but the application is outside its scope. The processor (as the specification calls it) is often referred to colloquially as an XML parser. Markup and content. The characters making up an XML document are divided into markup and content, which may be distinguished by the application of simple syntactic rules. Generally, strings that constitute markup either begin with the character < and end with a > , or they begin with the character & and end with a . Strings of characters that are not markup are content. However, in a CDATA section, the delimiters < ! In addition, whitespace before and after the outermost element is classified as markup. Tag. A tag is a markup construct that begins with < and ends with >. Tags come in three flavors. Element. An element is a logical document component that either begins with a start- tag and ends with a matching end- tag or consists only of an empty- element tag. The characters between the start- tag and end- tag, if any, are the element's content, and may contain markup, including other elements, which are called child elements. An example is < greeting> Hello, world!< /greeting>. Another is < line- break />. Attribute. An attribute is a markup construct consisting of a name. An example is < img src=. Another example is < step number=. An XML attribute can only have a single value and each attribute can appear at most once on each element. In the common situation where a list of multiple values is desired, this must be done by encoding the list into a well- formed XML attribute. Usually this is either a comma or semi- colon delimited list or, if the individual values are known not to contain spaces. An example is < ? Except for a small number of specifically excluded control characters, any character defined by Unicode may appear within the content of an XML document. XML includes facilities for identifying the encoding of the Unicode characters that make up the document, and for expressing characters that, for one reason or another, cannot be used directly. Valid characters. At the same time, however, it restricts the use of C0 and C1 control characters other than U+0. Horizontal Tab), U+0. A (Line Feed), U+0. D (Carriage Return), and U+0. Next Line) by requiring them to be written in escaped form (for example U+0. In the case of C1 characters, this restriction is a backwards incompatibility; it was introduced to allow common encoding errors to be detected. The code point U+0. Null) is the only character that is not permitted in any XML 1. Encoding detection. Unicode itself defines encodings that cover the entire repertoire; well- known ones include UTF- 8 and UTF- 1. XML also provides a mechanism whereby an XML processor can reliably, without any prior knowledge, determine which encoding is being used. For example: The characters . For example, it is legal to encode an XML document in ASCII, but ASCII lacks code points for Unicode characters such as . Consider the Chinese character . A user whose keyboard offers no method for entering this character could still insert it in an XML document encoded either as & #2. Similarly, the string . Comments cannot appear before the XML declaration. Comments begin with < !- - and end with - ->. For compatibility with SGML, the string . The ampersand has no special significance within comments, so entity and character references are not recognized as such, and there is no way to represent characters outside the character set of the document encoding. An example of a valid comment: < !- -no need to escape < code> & such in comments- -> International use. The following is a well- formed XML document including Chinese, Armenian and Cyrillic characters: < ? Some key points in the fairly lengthy list include: The document contains only properly encoded legal Unicode characters. None of the special syntax characters such as < and & appear except when performing their markup- delineation roles. The start- tag, end- tag, and empty- element tag that delimit elements are correctly nested, with none missing and none overlapping. Tag names are case- sensitive; the start- tag and end- tag must match exactly. Tag names cannot contain any of the characters ! An XML processor that encounters such a violation is required to report such errors and to cease normal processing. This policy, occasionally referred to as . This means that it contains a reference to a Document Type Definition (DTD), and that its elements and attributes are declared in that DTD and follow the grammatical rules for them that the DTD specifies. XML processors are classified as validating or non- validating depending on whether or not they check XML documents for validity. A processor that discovers a validity error must be able to report it, but may continue normal processing. A DTD is an example of a schema or grammar. Since the initial publication of XML 1. XML. Such schema languages typically constrain the set of elements that may be used in a document, which attributes may be applied to them, the order in which they may appear, and the allowable parent/child relationships. Document Type Definition. XML DTDs are simpler than SGML DTDs and there are certain structures that cannot be expressed with regular grammars. DTDs only support rudimentary datatypes. They lack readability. DTD designers typically make heavy use of parameter entities (which behave essentially as textual macros), which make it easier to define complex grammars, but at the expense of clarity. They use a syntax based on regular expression syntax, inherited from SGML, to describe the schema. Typical XML APIs such as SAX do not attempt to offer applications a structured representation of the syntax, so it is less accessible to programmers than an element- based syntax may be. Two peculiar features that distinguish DTDs from other schema types are the syntactic support for embedding a DTD within XML documents and for defining entities, which are arbitrary fragments of text and/or markup that the XML processor inserts in the DTD itself and in the XML document wherever they are referenced, like character escapes. DTD technology is still used in many applications because of its ubiquity. XML Schema. XSDs are far more powerful than DTDs in describing XML languages. They use a rich datatyping system and allow for more detailed constraints on an XML document's logical structure. XSDs also use an XML- based format, which makes it possible to use ordinary XML tools to help process them. RELAX NG schemas may be written in either an XML based syntax or a more compact non- XML syntax; the two syntaxes are isomorphic and James Clark's conversion tool. RELAX NG has a simpler definition and validation framework than XML Schema, making it easier to use and implement. It also has the ability to use datatype framework plug- ins; a RELAX NG schema author, for example, can require values in an XML document to conform to definitions in XML Schema Datatypes. Schematron. It typically uses XPath expressions. Schematron is now also an ISO/IEC standard (Part 3: Rule- based validation of the ISO/IEC standard DSDL). DSDL and other schema languages. DSDL includes RELAX NG full and compact syntax, Schematron assertion language, and languages for defining datatypes, character repertoire constraints, renaming and entity expansion, and namespace- based routing of document fragments to different validators. DSDL schema languages do not have the vendor support of XML Schemas yet, and are to some extent a grassroots reaction of industrial publishers to the lack of utility of XML Schemas for publishing. Some schema languages not only describe the structure of a particular XML format but also offer limited facilities to influence processing of individual XML files that conform to this format. DTDs and XSDs both have this ability; they can for instance provide the infoset augmentation facility and attribute defaults. RELAX NG and Schematron intentionally do not provide these. Related specifications. It is frequently the case that the term . Although XML Namespaces are not part of the XML specification itself, virtually all XML software also supports XML Namespaces. XML Base defines the xml: base attribute, which may be used to set the base for resolution of relative URI references within the scope of a single XML element. XML Information Set or XML Infoset is an abstract data model for XML documents in terms of information items.
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