1. 最简单的Schema文档如何写一个最简单的XML Schema文档呢？ 首先，我们写出一个最简单的XML文档。hello.xml
<? xml version="1.0" ?> < greeting > Hello World!! </ greeting > <!-- 一个根元素：greeting；且这个元素不含属性，无子元素，内容是字符串。 -->hello.xsd
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="greeting" type ="xsd:string" /> </ xsd:schema >XML Schema文档后缀名是.xsd，完全符合XML语法，根元素是schema，命名空间xmlns:xsd="http://www.w3.org/2001/XMLSchema，用元素<element>定义实例文档中的元素，如greeting。2. 含子元素的Schema文档 假设实例文档是如下的：customer.xml
< customer > < name > teiki </ name > < address > No.237, Road Waitan, Shanghai </ address > </ customer >则可以写出以下的XML Schema文档：customer.xsd
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="customer" > < xsd:complexType > < xsd:sequence > < xsd:element name ="name" type ="xsd:string" /> < xsd:element name ="address" type ="xsd:string" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:schema >实例文档customer.xml中，<customer>元素含有两个子元素，所以我们在Schema文档中采用ComplexType来定义该元素。sequence表示子元素依次出现的顺序。3. 含子元素和孙元素的Schema文档 这次我们给出一个更加复杂一些的文档：customer.xml
< customer > < name > Teiki </ name > < address > <!-- address追加一个地址子元素 --> < prefecture > Zhejiang </ prefecture > < city > Hangzhou </ city > < street > Xilu Road, No.121, 7F </ street > </ address > </ customer >为此，我们需要一个更加复杂一点的Schema文档：address.xsd
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="customer" > < xsd:complexType > < xsd:sequence > < xsd:element name ="name" type ="xsd:string" /> <!-- 追加子元素address --> < xsd:element name ="address" > < xsd:complexType > < xsd:sequence > < xsd:element name ="prefecture" type ="xsd:string" /> < xsd:element name ="city" type ="xsd:string" /> < xsd:element name ="street" type ="xsd:string" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:schema >不过，我们还可以采用ref元素来重新编写这个Schema文档：address2.xsd
< xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="customer" > < xsd:complexType > < xsd:sequence > < xsd:element name ="name" type ="xsd:string" /> < xsd:element ref ="address" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="address" > < xsd:complexType > < xsd:sequence > < xsd:element name ="prefecture" type ="xsd:string" /> < xsd:element name ="city" type ="xsd:string" /> < xsd:element name ="street" type ="xsd:string" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:schema >使用ref元素可以直接将其指向另一个模块，使文档更加具有可读性。
4. 定义相同子元素的数量先看这个简单的订购数据实例文档：order.xml
<? xml version="1.0" ?> < order > < orderItem > Accounting Book </ orderItem > < orderItem > Taxation Book </ orderItem > </ order >假设<orderItem>元素，即每次的订购书目不能超过10种，那该怎么写这个Schema文档呢？这里要用到<element>的maxOccurs属性。order.xsd--------------------
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element name ="orderItem" type ="xsd:string" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:schema >第7行中的maxOccurs属性为10，代表orderItem元素可以最大有10个。如果，不设定元素个数，则可以用maxOccurs="unbounded"来定义。类似，如果要定义最小值，可以使用minOccurs，比如下面这句：<xsd:element name="orderItem" type="xsd:string" minOccurs="5" maxOccurs="10"/>这两个属性缺省值都是1。5. 定义可选项的子元素假如上面的订书数据中，可以用书名或者书号任一一种订购，则实例文档可能如下：order2.xml-----------------
< order > < orderItem > <!-- 书名订购 --> < name > Accounting Book </ name > </ orderItem > < orderItem > <!-- 书号订购 --> < id > 7-5058-3496-7 </ id > </ orderItem > </ order >这时书写Schema文档还需要使用choice元素。order2.xsd
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element ref ="orderItem" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="orderItem" > < xsd:complexType > < xsd:choice > < xsd:element name ="name" type ="xsd:string" /> < xsd:element name ="id" type ="xsd:string" /> </ xsd:choice > </ xsd:complexType > </ xsd:element > </ xsd:schema >稍微更复杂的可选项子元素 再稍微修改一下订书数据的实例文档：order3.xml
< order > < orderItem > < name > Accounting Book </ name > < quantity > 2 </ quantity > </ orderItem > < orderItem > < id > 7-5058-3496-7 </ id > </ orderItem > </ order >这里假定<quantity>值为1时，缺省。如何修改Schema文档呢？order3.xsd-----------------
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element ref ="orderItem" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence > < xsd:choice > < xsd:element name ="name" type ="xsd:string" /> < xsd:element name ="id" type ="xsd:string" /> </ xsd:choice > < xsd:element name ="quantity" type ="xsd:string" minOccurs ="0" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > </ xsd:schema >19行中的quantity最少出现值为0，也就是可以有，也可以没有。当然，也可以直接在<choice>元素中，包含quantity,然后定义它的minOccurs。
6. 内置简单类型图省略7. 自定义简单类型 如果内置简单类型的44种还不能满足要求，怎么办呢？下面学习自定义简单类型。(XML的扩展性充分体现在这里)例如这个实例文档：order4.xml-----------------
< order > < orderItem > < id > 7-5058-3496-7 </ id > < quantity > 5 </ quantity > </ orderItem > </ order >ID是一个标准的ISBN编码，我们怎么定义这个ISBN编码呢？
< xsd:simpleType name ="idType" > < xsd:restriction base ="xsd:string" > < xsd:pattern value ="d{1}-d{4}-d{4}-d{1}" /> </ xsd:restriction > </ xsd:simpleType >idType是一个自定义的简单类型。我们对它做了限制：<xsd:restriction base="xsd:string">代表它是基于一个字符串类型。再用pattern元素来描述该字符串的形式。value="/d{1}-/d{4}-/d{4}-/d{1}"这是一个正则表达式，关于正则表达式，以后再介绍。嘻嘻！利用这个自定义的简单类型，我们可以重新写Schema文档：order4.xsd---------------
<? xml version="1.0" ?> < xsd:simpleType name ="idType" > < xsd:restriction base ="xsd:string" > < xsd:pattern value ="d{1}-d{4}-d{4}-d{1}" /> </ xsd:restriction > </ xsd:simpleType > < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element ref ="orderItem" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence > < xsd:element name ="id" type ="idType" /> < xsd:element name ="quantity" type ="xsd:integer" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:simpleType name ="idType" > < xsd:restriction base ="xsd:string" > < xsd:pattern value ="d{1}-d{4}-d{4}-d{1}" /> </ xsd:restriction > </ xsd:simpleType > </ xsd:schema >假如我们事先确定好ID只有3个，即只有3个ISBN是可选的，那怎么办？我们可以用enumeration元素来进行列举。
< xsd:simpleType name = " idType " > < xsd:restriction base = " xsd:string " > < xsd:enumeration value = " 7-5058-3496-7 " /> < xsd:enumeration value = " 7-5005-6450-3 " /> < xsd:enumeration value = " 7-3020-6069-7 " /> </ xsd:restriction > </ xsd:simpleType >再来看订购量quantity的值，如果我们设定其值必须在1－10之间，该怎么办呢？可以这些自定义一个简单类型。
< xsd:simpleType name ="quantityType" > < xsd:restriction base ="xsd:integer" > < xsd:minInclusive value ="1" /> < xsd:maxInclusive value ="10" /> </ xsd:restriction > </ xsd:simpleType >其中，minInclusive,maxInclusive分别代表该类型的取值范围。所以最终修改后的Schema文档如下：order4-1.xsd
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element ref ="orderItem" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence > < xsd:element name ="id" type ="idType" /> < xsd:element name ="quantity" type ="quantityType" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:simpleType name ="idType" > < xsd:restriction base ="xsd:string" > < xsd:enumeration value ="7-5058-3496-7" /> < xsd:enumeration value ="7-5005-6450-3" /> < xsd:enumeration value ="7-3020-6069-7" /> </ xsd:restriction > </ xsd:simpleType > < xsd:simpleType name ="quantityType" > < xsd:restriction base ="xsd:integer" > < xsd:minInclusive value ="1" /> < xsd:maxInclusive value ="10" /> </ xsd:restriction > </ xsd:simpleType > </ xsd:schema >8. 定义属性 最后，我们再来讲讲元素的属性如何在Schema文档中定义。比如上面的order.xml实例文档中：
< order > < orderItem id ="7-5058-3496-7" /> </ order >对此，我们在Schema文档中采用一个attribute来定义：order.xsd
< xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence > <!-- ←空元素 --> </ xsd:sequence > <!-- 定义该元素属性 --> < xsd:attribute name ="id" type ="xsd:string" /> </ xsd:complexType > </ xsd:element >那么，实例文档中该属性值是必须的还是可有可无的呢？我们可以这样限制：<xsd:attribute name="id" type="idType" use="required"/>这里我们讲id属性类型作为一种自定义数据类型idType。而且，用attribute元素的use属性来定义是否是必须的属性。required是必须值，optional是可选值，prohibited是无属性值。那么对于属性的缺省值，我们怎么定义呢？比如：<order><orderItem id="4-8443-1780-6" quantity="3"/></order>我们还可以用attribute元素的另一个属性default来定义：<xsd:attribute name="quantity" type="xsd:integer" default="1"/>所以，我们可以重新写出一个Schema文档：order2.xsd
< xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence ></ xsd:sequence > < xsd:attribute name ="id" type ="idType" use ="required" /> < xsd:attribute name ="quantity" type ="xsd:integer" default ="1" /> </ xsd:complexType > </ xsd:element >上面的属性我们定义我们还可以采用属性组的办法来重新改写Schema文档。 order3.xsd
< xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence ></ xsd:sequence > < xsd:attributeGroup ref ="orderItemAttributes" /> </ xsd:complexType > </ xsd:element > < xsd:attributeGroup name ="orderItemAttributes" > < xsd:attribute name ="id" type ="idType" use ="required" /> < xsd:attribute name ="quantity" type ="xsd:integer" default ="1" /> </ xsd:attributeGroup >这个属性组就不详细解释了，不过，大家一看就清楚了吧。最后，我们写一个完整的订书order.xml的Schema文档。
<? xml version="1.0" ?> < xsd:schema xmlns:xsd ="http://www.w3.org/2001/XMLSchema" > < xsd:element name ="order" > < xsd:complexType > < xsd:sequence > < xsd:element ref ="orderItem" maxOccurs ="10" /> </ xsd:sequence > </ xsd:complexType > </ xsd:element > < xsd:element name ="orderItem" > < xsd:complexType > < xsd:sequence ></ xsd:sequence > < xsd:attributeGroup ref ="orderItemAttributes" /> </ xsd:complexType > </ xsd:element > < xsd:attributeGroup name ="orderItemAttributes" > < xsd:attribute name ="id" type ="idType" use ="required" /> < xsd:attribute name ="quantity" type ="xsd:integer" default ="1" /> </ xsd:attributeGroup > < xsd:simpleType name ="idType" > < xsd:restriction base ="xsd:string" > < xsd:pattern value ="d{1}-d{4}-d{4}-d{1}" /> </ xsd:restriction > </ xsd:simpleType > </ xsd:schema >其他xml中引用xsd<?xml version="1.0" encoding="utf-8" standalone="no"?><Envlope xmlns="gmip" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="gmip_appraise_rep.xsd">Xsd中对应为：<?xml version="1.0"?><xsd:schema targetNamespace="gmip" xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="qualified">ElementFormDefault=”qualified” 意思是要求element使用的namespace是targetNamespace，它的作用是对元素起"限定与非限定"使用,意思是在文档范例中要求采用命名空间前缀。
