XML: DTD: Schema

1. The structure of the XML document can be abstracted up to two aspects: node and attribute

<Topnode name = "TOP">
<Midtop name = "mid"/>
</Topnode>

2. DTD Constraints

I. Peer nodes:

Constraints on nodes, it is obvious to describe the structure and type of nodes, etc.

<! Element name (type)>

All the descriptions in the DTD are completed by the above type.

See the following example:

A. <book> my book </book> --- DTD ---> <! Element book (# pcdata)>

B. <book/> --- DTD ---> <! Element book empty>

C. <book>
<Title> mybook </title>
<Author> yife </author> --- DTD ---> <! Element book (title, author)>
</Book>

* # Pcdata indicates character data

I don't need to explain more, so I should be able to understand it first, but now I will discuss the third case above:

D. <book>
<Title> mybook </title>
<Chapter> No.1 </Chapter>
...
Unknow, the number will be change sometimes
<Chapter> NO. n </Chapter>
</Book>

--- DTD ---> <! Element book (title, Chapter +)>

The wildcard table is provided here.
[Default]: Must be 1 time (1)
? : Must be 1 time or 0 (1 | 0)
+: 1 times or more (1... n)
*: 0 times or more (0... n)

E. <chapter> No.1 </Chapter>
<Chapter>
<Havechild/>
</Chapter>

--- DTD ---> <! Element book (# pcdata | (havechild)>

* The symbol "|" indicates the meaning of "or ".

Ii. attributes:

The attribute is bound to the node, and the attribute has no structure description.
<! Attilist element attribute type modifer>

Example:

A. <book Focus = "XML"/> --- DTD ---> <! Attilist book Focus CDATA # required>

* CDATA indicates a character.
* # Required indicates required. # impled indicates saving. # Fix indicates unchangeable.

In addition to characters, the attribute can also be enumerated.

B. <book Focus = "XML"/>
<Book Focus = "Java"/> --- DTD ---> <! Attilist book Focus (XML | Java) # impled>

C. <book Focus = "XML"> mE </book>
.....
<Book Focus = "XML"> You </book>

--- DTD ---> <! Attilist book Focus (XML | Java) "XML">

* "XML" is the default value, which is the default representation.

2. schema Constraints

I. Peer nodes: (schema also complies with XML standards)

<Element name = "name" type = "type" [Options...]>

Here types is more than DTD, very like Java

See the following example:

A. <book> my book </book>-schema --> <element name = "book" type = "string"/>

B. <book>
<Title> mybook </title>
<Author> yife </author>
</Book>

-Schema -->

<Element name = "book" type = "booktype"/>
<Complextype name = "booktype">
<Element name = "title" type = "string">
<Element name = "author" type = "string">
</Complextype>

C. You can write the code in the previous example (I hope you can think about the differences between the two methods)
<Element name = "book">
<Complextype>
<Element name = "title" type = "string">
<Element name = "author" type = "string">
</Complextype>
</Element>

A special example:

D. <author/>

-Schema -->

<Element name = "author">
<Complextype content = "booktype"/>
</Element>

Remember <! Element book (title, Chapter +)>? "+" In Schema:

E. <element name = "chapter" type = "string" minoccurs = "1" maxoccurs = "*">

In fact, minoccurs = "1" is not mandatory because the default value is 1.

Ii. attributes:

<Attribute name = "name" type = "type" [Options]>

Example:

A. <book Focus = "XML"/>

-Schema -->

<Element name = "book">
<Complextype>
<Attribute name = "Focus" type = "string"/>
</Complextype>
</Element>

* Attribute is an entry in complextype.

The schema does not contain # reuqired, so to express this meaning:

B. <attribute name = "Focus" type = "string" minoccurs = "1"/>

The default value of minoccurs is 0.

C. <attribute name = "Focus" type = "string" default = "XML"/> default value representation

D. schema representation <! Attilist book Focus (XML | Java) "XML">

<Attribute name = "Focus">
<Simpletype base = "string">
<Enumeration value = "XML">
<Enumeration value = "Java">
</Simpletype>
</Attribute>

3. xml usage:

Schema:
<Book xmlns: xsi = "http://www.w3.org/1999/XMLSchema/instance"
Xmlns = "you name space"
Xsi: schemalocation = "You XSD file location"
>

DTD:
<! Doctype book system "path to DTD file">