Website programming using PHP and XML (1)_PHP tutorial

1. Analysis of limitations of HTML

1. HTML has poor scalability. Although HTML should be sufficient for general applications, it has obvious shortcomings when dealing with symbols such as mathematics and chemistry, and it cannot be expanded, which greatly limits its development.

2. It cannot be automatically corrected after the link is lost. Since the URL address of a Web page changes frequently, the information must be modified manually when changing the URL address. Otherwise, a "404 URL address not found" message will be encountered, which greatly increases the workload of maintaining the Web page.

3. Data search takes a long time. Since HTML is mainly used to control the display of web pages, the same data has different storage formats in different web pages, making it impossible to quickly find the required information when performing data searches.

4.HTML does not have enough support for double-byte or multi-national characters. For example, Chinese information pages may not be displayed on different platforms.

It is precisely because of these shortcomings that people have studied Web page production languages ​​that can replace HTML. Among them, those already in use include Extensible Markup Language XML, Cascading Style Sheets (CSS), and Dynamic HTML (DHTML).

2. The composition of XML

Here are a brief list of several major XML technologies:

1.DTD (Document Type declaration)

The main function of DTD is to define the content mode of XML; limit the data range of XML tags; define the data type of attributes. However, because it is not written in XML, its scalability is relatively poor; and it only provides a limited number of data types, so its role is limited.

2.XML Schema

XML Schema functions similarly to 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, since it is written in XML, Schema has the following advantages compared with DTD:

◆XML Schema content model is open and can be expanded at will, while DTD cannot parse the expanded content.

◆DTD can only define the content type as a string, while XML Schema allows the content type to be defined as integer, floating point, Boolean or many other simple data types.

◆XML Schema uses Namespaces to connect special nodes in the document with the Schema. An XML file can have multiple corresponding Schemas, but an XML file can only have one DTD.

3.XLink

As a Web language, the linking ability of XML is very important. XML linking and addressing mechanisms include XLink, XPath and XPointer. XLink provides a powerful linking method that can establish one-way or multi-way complex connection relationships between documents, as well as a variety of linking functions such as annotation links, summary links, and extended link sets. XPath is used in XSLT and XPointer to support positioning relative to nodes and node sets in XML documents. XPointer provides positioning of the internal structure of the content of an XML document (such as a string or a selected paragraph) based on XPath. The linking capabilities of XML have been greatly enhanced compared to HTML.

4. CSS and XSL

A major feature of XML is the separation of content and format. That is to say, the XML document does not include how to display/represent the document. information. 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 completely uses XML syntax and is much more powerful than CSS.

5.DOM

Document Object Model (DOM) is a platform- and language-independent program interface that provides dynamic access and update of the content and structure of documents. with style means. The text can be processed further 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 includes three parts: core, HTML and XML. The core part of the DOM establishes a set of underlying objects that can represent any structured document. HTML and XML provide high-level interfaces that serve as more convenient document views. The DOM specification consists of objects and methods. Programmers use them to make it easier to access and manipulate certain types of documents.

6.Namespaces

Namespaces is a collection of all names that appear in the elements and attributes of an XML file, distinguished by URLs. In XML, users can define tags and elements themselves. Therefore, if multiple XML files are merged into one, conflicts are likely to occur. Namespaces solve this problem.

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http://www.bkjia.com/PHPjc/446674.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/446674.htmlTechArticle1. Analysis of the limitations of HTML 1. HTML has poor scalability. Although HTML should be sufficient for general applications, it has obvious shortcomings when dealing with symbols such as mathematics and chemistry, and...