Understand the role of xml

"Extensible Markup Language" (XML) provides a way to describe structured data. Unlike HTML tags, which are used primarily to control the display and appearance of data, XML tags are used to define the structure and data types of the data itself.
XML uses a set of tags to describe data elements. Each element encapsulates data that may be very simple or very complex. You can define an unlimited set of XML tags. For example, you can define some XML tags to declare data in the order, such as price, tax, shipping address, billing address, and so on. Because XML markup is adopted throughout and across organizations, data from a variety of different data stores will be easier to exchange and manipulate.
XML is a simple, platform-independent and widely adopted standard. The advantage of XML over HTML is that it separates the user interface from structured data. This separation of data and display makes it possible to integrate data from different sources. Customer information, orders, research results, bill payments, medical records, directory data and other information can be converted to XML.
XML vs. HTML
Here are a few key points to remember about the relationship between XML and HTML:
a.. XML is not meant to replace HTML; in fact, XML can be seen as a complement to HTML. XML and HTML have different goals: HTML is designed to display data and focuses on its appearance, while XML is designed to describe data and focuses on its content.
b.. Similar to HTML, XML does nothing. Although XML markup can be used to describe the structure of an item such as an order, it does not contain any code that can be used to send or process the order and ensure delivery of the order. Someone else must write code to actually perform these operations on the XML-formatted data.
c.. Unlike HTML, XML markup is defined by the schema or author of the document and is unlimited. HTML tags are predefined; HTML authors can only use tags supported by the current HTML standard.
Use of XML
XML is an extremely flexible way to transmit data. The following are all examples of where XML can be used:
a.. Ordinary documents
b.. Structured records, such as appointment records or orders
c.. Internet/Intranet Web applications that move data
d.. Objects with data, such as the persistent format of an object or ActiveX control
e.. Data records, such as the result set of a query
f.. Meta content of a Web site, such as "Channel Definition Format" ” (CDF)
g.. Graphical display, such as the user interface of an application
h.. Links to information and people on the Web
i.. C# code (can be in XML form); for more For information, see XML Document
j.. Discovery document used to locate available XML Web services; for more information, see XML Web Services Discovery.
The following lists several advantages of XML over other formats when storing information:
a.. XML formats are text-based, which makes them easier to read, easier to record, and sometimes easier to debug.
b.. XML documents can use much of the infrastructure already established for HTML, including the HTTP protocol and some browsers. HTTP allows the transmission of XML through firewalls.
c.. XML parsing is well defined and widely used, making it possible to retrieve information from XML documents in a variety of environments.
d.. Applications can rely on the XML parser for some structural validation and data type checking (when using schemas).
e.. XML is built on Unicode, making it easier to create international documents. However, XML is not suitable for every situation. XML documents tend to be more detailed than the binary formats they replace. They take up more network bandwidth and storage space, or require more processor time to compress. XML parsing may be slower than parsing highly optimized binary formats and may require more memory. However, careful application design can avoid some problems.
Validating XML Documents
To verify that an XML document contains the required data and structure, an XML schema must be associated with the XML document. XML Schema is the rules that define how elements and attributes are structured to form an XML document. You can share schemas between units to make it easy to transfer and process shared data. For more information, see Introduction to XML Schemas.
Displaying XML data
There are several ways to display (or provide) XML data.
There is also a data binding mechanism that can be used with stylesheets to display XML data in a visual form and add interactivity.
The following are several ways to display XML:
a.. XSLT — Extensible Stylesheet Language
b.. CSS — Cascading Style Sheets
c.. Microsoft Internet Explorer
XML Resources
If you are familiar with HTML, you can learn to create XML documents, as long as they are valid and conform to a standard format.
Q: Then why do many large websites still use html instead of xml?
A: XML and HTML are essentially different. You said that large websites use HTML. If it is static data, HTML is of course the fastest, but it is not well maintained! Generally, XML CSS is used for site design, but XML CSS has great limitations, so it is better to use XML ?
A: If it can be assumed that users all use (or at least have installed) IE6, there will be no problem.
If the user uses other browsers, XML->HTML conversion should be performed on the server side, which is not supported by ordinary static spaces. You can choose
ASP or PHP space that supports XMLDOM. Therefore the operating environment is different

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