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This article mainly introduces the xml constraint technology dtd example analysis, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

1. Official DTD tutorial

# # 2.xml constraint Technology:

DTD constraints: the syntax is relatively simple and the function is relatively simple. Appear first

Schema constraints: the syntax is relatively complex and the functionality is relatively powerful. In a way similar to xml syntax, Schema constraints appear to replace DTD constraints.

Introduction to 3.DTD:

The document type definition (DTD) defines a legitimate XML document building module. It uses a series of legal elements to define the structure of the document. DTD can be declared in a row in an XML document or as an external reference.

3.1 how to import DTD:

1. Internal import:

# Import method: # instance:] > ToveJaniReminderDon't forget me this weekend (second line) defines that this document is a document of type note (root tag).

(third line) defines that the note element has four elements (tags): "to, from, heading, body"

(line 4) define the to element as "# PCDATA" type

(line 5) define the frome element as "# PCDATA" type

(line 6) define the heading element as "# PCDATA" type

(line 7) define the body element as "# PCDATA" type

External import method:

Local file:

# Import method: # note.dtd file content:

Public external import: general projects use public external import. For example, ssh's xml file basically adopts this method.

# Import method: # such as hibernate.cfg.xml:3.2DTD syntax:

1. Constraint label

Syntax:

Or category:

Empty tag: EMPTY. Indicates that the element must be an empty element. For example:

Normal string: (# PCDATA). Indicates that the content of the element must be a normal string (cannot contain child tags). For example:

Anything: ANY. Indicates that the content of an element can be any content (including child tags) for example:

Element content:

Order problem:: the number of sub-tags in order: tags: must and only occur once. Label +: the label appears at least once *: 0 or n times. Label? : 0 or 1 time. Declare "not. / both." Content of the type

two。 Constraint attributes:

Syntax:

Attribute type:

CDATA: indicates a normal string (en1 | en2 |..): indicates that it must be one of the optional values ID: indicates that the attribute value must be unique in an xml document. Value cannot start with a number

Default value:

# REQUIRED attribute value is required # IMPLIED attribute is not required # FIXED value attribute is not required, but property value is fixed

3.3 the tests are as follows. Please take a closer look at the notes:

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