A Brief History of XML
XML appeared in 1998 and is based on the standardized generalized markup language (SGML). SGML is another language that defines international standard documents that can be considered as the language you define. HTML is based on SGML. One of the main problems is difficult to say about SGML. XML aims to make it much easier. XML also owes much of its life to HTML.
Aimed at displaying HTML content; you could not use it for advanced features such as sorting and filtering. HTML was not a very accurate language, and it did not depend on the register. It was possible to mistype the HTML content, but for the browser to display the page correctly. XML solves many of the shortcomings of HTML. In 1999, HTML was rewritten using the rules for creating XML as XHTML.
Building rules An XHTML document is more accurate than an HTML document. The severity of these rules depends on which document type declaration (DOCTYPE) you assign to the XHTML sheet. I will explain more about DOCTYPE in Chapter 3. Since 1998, it has become clear that XML is a very powerful way to manage information. XML documents allow you to share data. A number of W3C – related suggestions for converting, rendering, and navigating XML documents.
Let’s summarize the following key points:
• XML is not a language; its rules are used to create other languages.
• Creates languages based on tags that mark XML content.
• XHTML is one of the languages that created XML as an HTML transformation.
• XML is based on SGML.
XML Goals After the complexity of SGML, the W3C became very clear about its goals for XML. You can see http://www.w3.org/TR/REC-xml/#sec-origin-goals for the following purposes:
1. XML can be used directly on the Internet.
2. XML should support a variety of applications.
3. XML must be compatible with SGML.
4. It’s easy to write programs that process XML documents.
5. The number of additional features in XML should be kept to an absolute minimum, preferably zero.
6. XML documents should be clear and understandable to humans.
7. XML design should be prepared quickly.
8. XML design must be formal and clear.
9. Creating XML documents is easy.
10. Accuracy in XML designation is minimal.
There are a few things to note about these goals. First, W3C wants XML to be simple; In fact, several goals include the concepts of “easy” and “clear”.
Second, W3C gave XML two goals: people and XML processors. An XML processor or analyzer is software that processes an XML document. Processors can define the content of an XML document; read, write and edit an existing document; or create a new one from scratch.
The goal here is simple for XML processors, developing them and opening up a market for them. Strict construction rules mean less processing is required. This in turn can target XML documents to portable devices such as cell phones and PDAs.
By keeping the documents readable, you can easily access the data, and easily create and edit possible applications. Using Unicode allows developers to create XML documents in different languages. Unfortunately, the necessary side effect is that XML documents can be meaningful, while describing data using XML can be a longer process than other procedures.
|XML supports a set of Unicode characters that allow multilingual support. Unicode 231 supports characters. This includes all the characters you may need, as well as characters you may never see. You can use an 8-bit Unicode Conversion Format (UTF-8) to encode Unicode characters. characters use the codes used in ASCII. Of course, these systems provide good compatibility with adults. Languages such as Japanese and Chinese need UTF-16 encoding. You can learn more about Unicode at http://www.unicode.org.|
Third, pay attention to the term XML document. This term is a more specific document than the traditional view of a. Some XML documents exist physically, while others are created in the form of a flow of information according to the rules of creating XML. As an example, it calls web services and databases whose content is returned in XML format. Now that you understand what XML is, let’s look at the rules for creating XML languages.