Web site programming using PHP and XML (1) _php tutorial

analysis of the limitations of HTML

The scalability of the 1.HTML is poor. Although as a general application, HTML should be sufficient, but in the processing of mathematical and chemical symbols, HTML has obvious shortcomings, and it can not be extended, so that its development has received a great deal of limitations.

2. Cannot be corrected automatically after the link is lost. Because the URL address of the Web page often changes, and in changing the URL address must manually modify the information, otherwise you will encounter "404URL address not Found" information, which greatly increased the maintenance of the Web page.

3. Data search for a long time. Since HTML is primarily used to control the display of a Web page, the same data can be stored in different formats in different Web pages, so that data searches cannot be quickly found.

4.HTML support for double-byte or multi-country text is not enough. For example, the Chinese information page will appear under different platforms, such as the problem can not be displayed.

Because of these shortcomings, people have studied the Web page making language that can replace HTML. It has been put into use: Extensible Markup Language XML, cascading style sheets (CSS), and Dynamic HTML (DHTML).

Second, the composition of XML

Here is a brief list of some of the main XML technologies:

1.DTD(document type Declaration)

The main function of a DTD is to define the content schema of the XML, limit the data range of the XML tag, and define the data type of the attribute. However, because it is not written in XML, extensibility is poor, and only a limited number of data types are provided, so it has a limited role.

2.XML Schema

The XML schema works like a DTD. But the difference is that the schema file describes the specific types of elements and attributes in the XML file that references it. In addition, because it is written in XML, schema and DTD compare the following advantages:

The XML schema content model is open and can be arbitrarily expanded, and the DTD cannot parse the expanded content.

A DTD can only define a content type as a string, whereas an XML schema allows a content type to be defined as Integer, float, Boolean, or many other simple data types.

XML Schema uses namespaces to associate a particular node in a document with a schema, an XML file can have multiple schemas, and an XML file can have only one DTD.

3.XLink

As a Web language, the ability to link XML is very important. The links and addressing mechanisms of XML include XLink, XPath, and XPointer. XLink provides powerful linking methods to create a one-way or multi-directional complex join relationship between documents, as well as a number of links such as comment links, summary links, extended link sets, and more. XPath is used in XSLT and xpointer to support positioning in XML documents relative to nodes and node sets. XPointer provides the positioning of the internal structure of the content of an XML document, such as a string or a selected paragraph, on an XPath basis. The ability to link XML is greatly enhanced than HTML.

4.CSS and XSL

One of the major features of XML is the separation of content from the format, meaning that the XML document does not contain information about how to display/represent the document. CSS and XSL (XML Style Language) solve the problem of displaying XML documents.

CSS (cascading style sheets) can also be used in HTML and XML. XSL uses the syntax of XML completely, which is much more powerful than CSS.

5.DOM

The Document Object Model (DOM) is a platform-language-agnostic program interface that provides the means to dynamically access and update the content, structure, and style of a document. The text can be treated as further processing, and the results of the processing are updated to the presentation page.

The goal of DOM is to define a standard programming interface for XML and HTML, which consists of the core, HTML, and XML three parts. The core part of the DOM establishes a set of underlying objects that can represent any structured document. HTML and XML provide a high-level interface that can be used as a more convenient document view. The DOM specification consists of objects and methods. Programmers use them to make it easier to access and manipulate specific types of documents.

6.Namespaces

Namespaces is a collection of all the names that are distinguished by URLs and that appear in the elements and attributes of an XML file. In XML, users can define their own tags and elements. Therefore, if you merge multiple XML files into one, there is a good chance of a conflict. namespaces solved the problem.

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