请给小弟我解释下这个服务器描述语言是什么意思？

<?xml version='1.0' encoding='UTF-8'?><br /><br /><!-- WSDL file generated by Zend Studio. --><br /><br /><definitions name="soap" targetNamespace="urn:soap" xmlns:typens="urn:soap" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns="http://schemas.xmlsoap.org/wsdl/"><br />	<message name="auth"><br />		<part name="email" type="xsd:string"/><br />		<part name="password" type="xsd:string"/><br />	</message><br />	<message name="authResponse"><br />		<part name="authReturn" type="xsd:boolean"/><br />	</message><br />	<message name="latest"><br />		<part name="date" type="xsd:integer"/><br />	</message><br />	<message name="latestResponse"><br />		<part name="latestReturn" type="xsd:string"/><br />	</message><br />	<message name="send"><br />		<part name="email" type="xsd:string"/><br />		<part name="password" type="xsd:string"/><br />		<part name="message" type="xsd:string"/><br />	</message><br />	<message name="sendResponse"><br />		<part name="sendReturn" type="xsd:boolean"/><br />	</message><br />	<portType name="chatPortType"><br />		<operation name="auth"><br />			<input message="typens:auth"/><br />			<output message="typens:authResponse"/><br />		</operation><br />		<operation name="latest"><br />			<input message="typens:latest"/><br />			<output message="typens:latestResponse"/><br />		</operation><br />		<operation name="send"><br />			<input message="typens:send"/><br />			<output message="typens:sendResponse"/><br />		</operation><br />	</portType><br />	<binding name="chatBinding" type="typens:chatPortType"><br />		<soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/><br />		<operation name="auth"><br />			<soap:operation soapAction="urn:chatAction"/><br />			<input><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</input><br />			<output><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</output><br />		</operation><br />		<operation name="latest"><br />			<soap:operation soapAction="urn:chatAction"/><br />			<input><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</input><br />			<output><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</output><br />		</operation><br />		<operation name="send"><br />			<soap:operation soapAction="urn:chatAction"/><br />			<input><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</input><br />			<output><br />				<soap:body namespace="urn:soap" use="encoded" encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/><br />			</output><br />		</operation><br />	</binding><br />	<service name="soapService"><br />		<port name="chatPort" binding="typens:chatBinding"><br />			<soap:address location=""/><br />		</port><br />	</service><br /></definitions><br />