Programming Using PHP and XML to perform website programming code examples

1. Small sequence
　HTML is easy to learn and versatile. General PHP programs are embedded in the HTML language. However, as the WEB becomes more and more widely used, the weaknesses of HTML are becoming more and more obvious. The emergence of XML makes up for these shortcomings. It provides a universal method that can handle all data on the Internet.
　2. 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 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).
　3. The composition of XML
　 Here is 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
　The function of XML Schema is similar to that of 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 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, and 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
　One of the characteristics of XML is the separation of content and format. That is to say, the XML document does not contain information on 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 completely uses XML syntax and is much more powerful than CSS.
　5. DOM
　The Document Object Model (DOM) is a platform- and language-independent program interface that provides a means to dynamically access and update the content, structure, and style of a document. The text can be processed further and the results of the processing can be updated to the presentation page.
　The goal of DOM is to define a standard programming interface for XML and HTML, which includes core, HTML and XML parts. 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 elements and attributes of XML files, 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.
　4. PHP’s support for XML
　 PHP provides powerful support for XML. It uses an XML "parser", and in order to support this parser, it provides 20 (PHP4) XML parsing functions. Below are some of the most commonly used PHP parsing functions.
　1. xml_parse
boolean xml_parse(int parser, string data, int [isFinal]);
　This function is used to parse file data in XML format. The parameter parser is the parsing code. The parameter data is the parsed data block (chunk). The parameter isFinal can be omitted. If set to true, the system will automatically send the last piece of data to the data parameter. If there are no errors, return true value.
　2. xml_parser_create
int xml_parser_create(string [encoding]);
　This function is used to initialize a new XML parser. The parameter encoding can be omitted and is the character set used by XML. The default value is ISO-8859-1. There are two other options: US-ASCII and UTF-8. If successful, it will return parser code for use by other functions, if it fails, it will return false value.
　3. The parameter parser is the parsing code. The parameters startElementHandler and endElementHandler are the headers of the start and end of the element respectively. The startElementHandler must include the parsing code, name, and attributes, while the endElementHandler parameter includes the parsing code and name. If there are no errors, return true value.
　4. xml_set_character_data_handler
boolean xml_set_character_data_handler(int parser, string handler);
　This function configures the header of character data. The parameter parser is the parsing code. The parameter handler includes two elements: parsing code and data string. If there are no errors, return true value.
　5. xml_get_error_code
int xml_get_error_code(int parser);
　This function can obtain the error code during XML processing. The parameter parser is the parsing code. If the parser has an error, it returns a false value, otherwise it returns an error code (such as XML_ERROR_BINARY_ENTITY_REF.... etc.).
　6. xml_error_string
string xml_error_string(int code);
　This function can obtain the error code during XML processing. The parameter code is the parsing error code. If there is no error, the return value is a text description string of the code.
　7. xml_get_current_line_number
int xml_get_current_line_number(int parser);
　This function is used to obtain the line number currently being processed by XML parsing. The parameter parser is the parsing code. If parser has an error, it returns a false value, if there is no error, it returns a line number.
　8. xml_parser_free
boolean xml_parser_free(int parser);
　This function is used to release the memory currently used for XML parsing. The parameter parser is the parsing code. If there is no error, return a true value, otherwise return a false value.
The above introduces the coding examples of website programming using PHP and XML, including programming content. I hope it will be helpful to friends who are interested in PHP tutorials.