XML, the so-called XML, is extensible Markup Language, translated into Chinese is "extensible identity language", many people in the country understand the XML for the simple extension of HTML, which is actually a misunderstanding. Although XML is very closely related to HTML.
The relationship between XML and SGML, HTML.
SGML and HTML are pioneers of XML. SGML refers to the "Universal Identification Language Standard" (Standard generalized Markup Language), which is the international standard for defining the structure and content of electronic files, and is a very complex document structure, It is mainly used in the defense area of a large number of highly structured data and various other industrial fields, which facilitates classification and indexing. The definition is powerful compared to XML, with the disadvantage that it does not apply to Web data descriptions, and that SGML software prices are very expensive. HTML believes that everyone is familiar with the "Hypertext Markup Language" (Hypertext Identification language), its advantage is more suitable for Web page development. But it has a disadvantage is that the tag is relatively small, only fixed set of tags such as <p>.<strong>. Lacks the flexibility and adaptability of SGML. Cannot support a specific domain of markup language, such as mathematics, chemistry, music and other areas of support for less. For example, it is difficult for developers to represent mathematical formulae, chemical formulas, and musical scores on web Pape.
XML combines the advantages of SGML and HTML and eliminates its drawbacks. XML is still considered to be an SGML language. Simpler than SGML, but most of the functionality of SGML can be achieved. In the summer of 1996, John Bosak of Sun Microssystem began developing the SGML workgroup (now called an XML workgroup). Their goal is to create a SGML that enables it to take advantage of SGML and preserve the simplicity of HTML in the Web. Now the goal is basically achieved.
Second, the development of XML.
In the area of specialization, there are many projects in the Web Markup language, the famous cml-Chemical Markup Language, developed by Peter Murray_rust, and the first universal XML browser Jumbo. In mathematics, including IBM, which has been working on the development of MathML April 1997, has published the first version of XLL. When XLL is fully implemented, it is more complex and powerful than the level of links reached by HTML and the current browser. Microsoft and Inso introduced XSL in August 1997. Because XML is pure structure and semantics, you need to describe a single element format method. You can use HTML CSS, and another scenario is XSL. The msxsl program was published in January 1998 by Microsoft Corporation. You can use XSL tables and XML documents to create HTML pages that can be IE4 recognized. The official version of Xml1.0 was released in February 1998 by the consortium. In recent more than a year, because of the rapid development of network applications, the development of XML is very rapid. With the advent of the DOM (Document Object Model), the transformation of XSLT (XSL), and the rapid development of XML application software, Microsoft, IBM, Breeze, Stilo and other companies have launched their own or parser, or development platform. Driven by large companies such as MICROSOFTIBM and HP, there are currently two well-known XML research organizations, Biztalk.com and Oasis.org, who propose standard recommendations to the consortium. BizTalk is a Microsoft-led organization, and it's interesting that Microsoft has joined the Oaisis, but unlike other prestigious companies such as IBM and HP, his annual fee is only $100,000, with a Microsoft spokesperson saying " It all depends on the development of Oasis! The implication is that a standard war is inevitable if the standards set by OASIS are incompatible with Microsoft's application.
What is XML
First of all, XML is a Meta markup language, the so-called "meta tag" is the developer can define their own needs according to their own requirements, such as developers can define the following tags <book> <name> any name that satisfies the XML naming convention can be labeled, This opens the door for different applications. HTML is a predefined markup language that only recognizes tags that are already defined, such as <dt> Book Name
<dd> author_name <ul> <li>publisher_name;;;; <li>isbn_number <ul> in XML, the same data is represented as <book> <title>book name</title> <author> Author Name</author) <publisher> publisher name</publisher> <isbn>isbn_number</isbn> < /book> from the above, it can be seen that XML documents are clearly semantic and structured. XML is a common data format from a low-level perspective, XML is a simple data format, is pure 100% ASCII text, and ASCII's ability to resist the damage is very strong. Unlike compressed data and Java objects, it is not readable as long as it destroys a data file. From an advanced point of view, it is a self-describing language.
XML can be leveraged for data exchange primarily because the information represented by XML is independent of the platform, where the platform can be understood as different applications or different operating systems; It describes a specification that enables Microsoft's Word documents to be used with Adobe Acrobat exchanges information and can exchange information with the database.
The structured data represented by XML.
For large, complex documents, XML is an ideal language that allows you to specify not only the words in a document, but also the relationships between elements. For example, you can specify that a author element must have a name child element. It can be stipulated that the business of the enterprise must include what sub business.
XML document. XML documents consist of DTDs and XML literals, the so-called DTD (document Type Definition), which is simply a syntax rule for a set of tags. indicates how the XML text is organized, such as a DTD can represent a <book> You must have a child tag <author>, you can have or no child tags <pages>, and so on. Of course a simple XML literal can have no DTD. The following is a simple XML literal. ? XML version= "1.0" standalone= "yes" > <book> haha </book> where? The beginning and end is the process description. Standalone represents a peripheral device. Here the peripherals can be understood to be that the XML text does not have other files applied. Because XML files can externally apply external data such as DTDs.
Some of the technologies involved in XML.
XSL and CSS.
As you can see through the preceding introductions, XML can define the content of information without defining how it should be expressed, which is actually the advantage of XML, which separates the content from the form, so that the same content can be expressed differently, believing that with the improvement of XML application, the kind of "suggest you use 800x600 resolution" Will disappear. The expression of XML content is achieved through XSL (XML style Language) and CSS (cascading style Sheets cascading stylesheets). Take the previous example, the style sheet (XSL) that you can define for the XML document is as follows: <xsl> <rule> <root/> <H1> <children/> </H1> < /rule> <xsl> This is a simple XSL file that uses msxsl to generate HTML files. as follows XML Schemas Although DTDs impose restrictions on the use of tokens, automatic processing of XML requires more rigorous and comprehensive tools. For example, a DTD does not guarantee that the value of one attribute of a tag must not be negative, and an XML schema appears, because XML schemas (unlike DTDs) themselves are a regular XML document, so developers can use the same tools to process their exchange of information with other XML. The original XML schema was presented by Microsoft, and the experts in the Consortium were fully discussed and demonstrated, and in February of 1999, a requirements definition was released stating the requirements that schemas must meet, and in May, the consortium completed and published a schema definition. Currently, XML parsers in IE5 can parse XML based on document type definition (DTD) or XML Schema
With regard to the DOM DOM, document Object model, which implements the contents of an XML document as an object modeled simply as how an application accesses an XML document, DOM Level 1 of the consortium defines how to implement attributes, methods, events, and so on.
About XSLT XSLT, XML Stylesheet Language transformation. Formal standards have not yet been formally formed in the writing of this article, and the XSLT was adopted in November in 1999. XSLT is a language that is used to transform XML documents into one another. To put it simply, we know that different developers use different XML documents for their respective applications, using XSLT we can extract the data we need from a defined XML document, form different forms, XML, HTML, and various script.
About XPointer and Xlinks
Similar to Hyper Link in HTML. XPointer and XLink are used to join parts of other XML documents and other XML documents, where XPointer is equivalent to the anchor used in HTML to locate HTML content! But the level of connectivity is even stronger. For example, in the bookstore, you can locate a writer called Jin Yong, the book has four villains of the book, in the HTML, this is impossible to achieve.
Of course, the development of XML has led to the emergence of many new technologies, as well as RDF, Xfrom, and so on, most of which are just suggestions, not formal standards, and some are even in the discussion stage. We will keep a close eye on the changes in the content.
XML Framework
The so-called frame is the framework. XML is a common standard. It's not personal, it's not a company, it's a consortium. So why are so many big companies pointing to such mo? The companies that compete with each other are its framework, its schema. XML framework is a kind of high-level structure control, which is the structure of managing XML files. Using the XML framework, the business logic (business logic) can be separated from the data and computing. The current well-known framework, Microsoft BizTalk and the United Nations (UN/CEFACT) and Oasis Alliance, launched the ebXML motion at the end of 99. I believe there will be many framwork in the near future. One of the problems is that the introduction of the framework is not an adventure when many things about XML in the consortium are still being suggested. However, the development of the Internet seems to be the case, we will wait and see about the development of Framwwork.
