前面说了一些Google API的介绍，但是在实际的开发当中，我们可能需要把Google RESTful API返回的JSON数据转换成XML数据输入到第三方系统，这在企业应用集成里面非常的常见。那么里面就有一个问题，如何确保转换后的XML数据格式是规范的，这就需要XML Schema(XML)来进行校验。现在关键是，我们只知道Google API的JSON的schema，但是Google RESTful并没有提供返回数据的XML的schema，那么XML的Schema将会是什么样子的呢？让我以Google Tasks API为例子。从下面的URL我们可以看到Google Tasks RESTFul的API JSON Schema的信息：https://www.googleapis.com/discovery/v1/apis/tasks/v1/rest

那么，如何把Google Tasks的JSON Schema转换成XML的XSD Schema？XML的Schema将会是什么样子的呢？请参考下面转换实现。

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
    <xs:complexType name="Task">
        <xs:sequence>
            <xs:element name="completed" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="deleted" form="unqualified" type="xs:boolean" minOccurs="0"/>
            <xs:element name="due" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="etag" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="hidden" form="unqualified" type="xs:boolean" minOccurs="0"/>
            <xs:element name="id" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="kind" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="links" form="unqualified" type="Tasklinks" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element name="notes" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="parent" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="position" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="selfLink" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="status" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="title" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="updated" form="unqualified" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="TaskList">
        <xs:sequence>
            <xs:element name="etag" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="id" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="kind" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="selfLink" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="title" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="updated" form="unqualified" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="TaskLists">
        <xs:sequence>
            <xs:element name="etag" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="items" form="unqualified" type="TaskList" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element name="kind" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="nextPageToken" form="unqualified" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="Taskitems">
        <xs:sequence>
            <xs:element name="description" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="link" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="type" form="unqualified" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="Tasklinks">
        <xs:sequence>
            <xs:element name="items" form="unqualified" type="Taskitems" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>
    <xs:complexType name="Tasks">
        <xs:sequence>
            <xs:element name="etag" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="items" form="unqualified" type="Task" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element name="kind" form="unqualified" type="xs:string" minOccurs="0"/>
            <xs:element name="nextPageToken" form="unqualified" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexType>
    <xs:element name="Task" type="Task"/>
    <xs:element name="TaskList" type="TaskList"/>
    <xs:element name="TaskLists" type="TaskLists"/>
    <xs:element name="Tasks" type="Tasks"/>
</xs:schema>