XML learning notes (2)

XML is a source label language that can be seen as a tool used to generate a lack language. The so-called standard language is like the
of HTML.

From the beginning, we have been talking about how XML "files", but it should be pointed out that the word "file" may be misleading. In addition to the usual files, the XML markup language can be transmitted in accordance with the data stream, database result set, and results dynamically generated by the application. Therefore, what we said is actually a broad file, more accurate call should be a "data object", but for the sake of simplicity, we still call it "file".

In the future, we will also see the skills of XML applications in data.

XML files should be "well-final" (Well-Formed)

Let's take a paragraph XML

[1] [2] [3] [4] [5] XML [6] XML is an expandable source labeled language, it can be used to specify new Schedule, and organize data according to this rule [7] [8] [9] [11 ] Zhang 3 [12] zhang@aaa.com [13] [14]]]> [15] [16] < / Special Noun> [17]

The most basic composition of an XML file is

XML declaration processing indication (optional) XML element

In this example, [1] is an XML declaration, [3] - [17] is the individual elements in the file.

In addition, other logic elements that appear in the above example are:

[1] [2] is the processing instruction [8] is the comment [9] - [14] is CDATA in [5] line " XML " "is a tag," XML "is character data.

XML declaration

Let's take a look at the specific meaning of these properties: