翻譯自 The Difference Between RPC and Document Style WSDL rpc和document到底是什么意思？他們如何同"encoded/literal"相關聯？二者的沖突來自哪里？ binding的style和use 通常情況下，web服務是由一個wadl文件來描述的的。在這個文件中，抽象的描述所支持的web服務操作和消息，然后關聯到一個具體的網 絡歇息和消息格式。典型的wsdl文件由這個幾個元素組成:tyoes,message.porttype用來描述抽象的定義;biding和service指定具體的實 現。所有的這些元素包裝在definitions元素中。 在binding元素中，rpc和document是最值得我們關注的元素。wsdl 的 binding描述了如何將service關聯到消息協議；這些消息協議是 http，mime，soap中的任意一種。不過，實際中，soap是最常用的協議；rpc和document的區別也是在soap的下的區別（it is SOAP that the RPC/document distinction refers to）。通常http(s)是傳輸soap消息的協議。 <wsdl:binding>元素包含一對參數，style(rpc|document)和use(encoded|literal)，他倆會影響到soap消息的格式.他們的使用方式如下 ： <wsdl:binding name="Config1Binding" type="prt0:CreditLimitLocalWebServiceVi_Document"> <soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document" /> <wsdl:operation name="creditLimitCheck"> <soap:operation soapAction="" /> <wsdl:input> <soap:body use="literal" parts="parameters" /> </wsdl:input> <wsdl:output> <soap:body use="literal" /> </wsdl:output> </wsdl:operation> </wsdl:binding> style屬性: wsdl1.1要求binding的style要么是rpc要么是doucment。這個選擇與如何組織soap的負荷相關。下面是分別他們如何影響<soap:body>內 容的細節。 document：<soap:body>的內容由定義在<wsdl:type>中的xml模式指定。他不需要遵循特定的soap規范。簡言之，soap消息是通過 <soap:body>中的document發送出去，而沒有額外的要遵循的格式規則。document style是一種默認的選擇。 rpc： <soap:body>元素的結構需要遵循特定的規則（soap1.1規范第7部分有細節）。根據這些規則，<soap:body>可以包含唯一一個元素 ，這個元素在operation后被命名，所有的參數都必須寫成這個元素的子元素。 因為可以自由的選擇哪種消息格式，遵循document格式的soap消息看上去很像rpc格式。 現在，決定性的問題是：選擇其中任意一個選項后的結果是什么樣？為何要選擇rpc或者document？很多情況下，選擇他們后，soap消息 的格式看起來很相像，那么為什么還要提供這種選擇呢？原因要從soap標準化的歷程中尋找。 use屬性 這個屬性指定了soap消息的編碼規則。他同樣在<wsdl:binding>元素中完成。他的值為encoded或者literal. 他引用了一系列規則，soap客戶端和soap服務端都遵循這些規則以解釋<body>元素中的內容。 use="literal" 意味著type定義遵循xml模式定義 use="encoded" 參考xml中已有的應用數據，通常指的是soap1.1規范中的soap編碼規則。如果文檔中沒有自定義數據，就可以選擇 encoded。 附文章全文： The Difference Between RPC and Document Style WSDL Summary RPC style and document style are catchphrases frequently heard in the context of web services and the SOAP protocol. What exactly do they mean? How do they relate to the pair of terms "encoded/literal"? Where does the confusion about these terms come from? This article describes the WSDL binding style and use attributes. By Susanne Rothaug 20 Nov 2004 Binding Style and Use A web service is usually described by a WSDL (Web Services Description Language) document. In this document, the supported web service operations and messages are described abstractly and then bound to a concrete network protocol and message format. A typical WSDL document consists of the following elements: "types," "message," and "portType" for the abstract definitions; "binding" and "service" for the concrete specification. All of these elements are wrapped inside a "definitions" element. In the context of RPC and document style, it is the binding element that we need to take a closer look at. A WSDL binding describes how the service is bound to a messaging protocol, either HTTP GET/POST, MIME, or SOAP. In practice, SOAP is the most universally used protocol; it is SOAP that the RPC/document distinction refers to. Usually HTTP(S) is used as transport protocol for the SOAP message – "SOAP over HTTP(S)." The <wsdl:binding> element of the WSDL contains a pair of parameters that influence the form of the resulting SOAP messages: binding style (RPC or document) and use (encoded or literal). See how style and use are defined in the WSDL fragment below: <wsdl:binding name="Config1Binding" type="prt0:CreditLimitLocalWebServiceVi_Document"> <soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document" /> <wsdl:operation name="creditLimitCheck"> <soap:operation soapAction="" /> <wsdl:input> <soap:body use="literal" parts="parameters" /> </wsdl:input> <wsdl:output> <soap:body use="literal" /> </wsdl:output> </wsdl:operation> </wsdl:binding> The "Style" Attribute WSDL 1.1 specifies the style of the binding as either RPC or document. This choice corresponds to how the SOAP payload - i.e., how the contents of the <soap:Body> element - can be structured. Here are some details of how each style affects the contents of <soap:Body>: Document: the content of <soap:Body> is specified by XML Schema defined in the <wsdl:type> section. It does not need to follow specific SOAP conventions. In short, the SOAP message is sent as one "document" in the <soap:Body> element without additional formatting rules having to be considered. Document style is the default choice. RPC: The structure of an RPC style <soap:Body> element needs to comply with the rules specified in detail in Section 7 of the SOAP 1.1 specification. According to these rules, <soap:Body> may contain only one element that is named after the operation, and all parameters must be represented as sub-elements of this wrapper element.
As a consequence of the freedom of choice that the document style offers, the SOAP messages conforming to a document style WSDL may look exactly the same as the RPC equivalent. The decisive question now is: What are the consequences of choosing one option or another? Why choose RPC over document, or document over RPC? In many cases, the SOAP messages generated from either RPC or document style WSDLs look exactly the same - so why offer the choice at all? The reason may be found in the history of the SOAP standard. SOAP has its roots in synchronous remote procedure calls over HTTP and the appearance of the document accordingly followed these conventions. Later, it was seen as a simplification to use arbitrary XML in the SOAP body without adhering to conventions. This preference is reflected in the document style WSDL documents. So far, both options are represented in the WSDL specification and the choice of one or the other is mainly a question of personal taste since most SOAP clients today accept both versions. The "Use" Attribute The use attribute specifies the encoding rules of the SOAP message. This is also done within the <wsdl:binding> element, as seen in the example above. The value can be encoded or literal. It refers to the serialization rules followed by the SOAP client and the SOAP server to interpret the contents of the <Body> element in the SOAP payload. use="literal" means that the type definitions literally follow an XML schema definition. use="encoded" refers to the representation of application data in XML, usually according to the SOAP encoding rules of the SOAP 1.1 specification. The rules to encode and interpret a SOAP body are in a URL specified by the encodingStyle attribute. Encoded is the appropriate choice where non-treelike structures are concerned, because all others can be perfectly described in XML Schema.
The combination of the style and use attributes leads to four possible style/use pairs: RPC/encoded RPC/literal document/encoded document/literal
Some of these combinations are rarely used in practice, such as document/encoded. In general, the literal use is gaining importance, and as far as RPC/encoded is concerned, the Web Services Interoperability Organization (WS-I) in its Basic Profile Version 1.0a of August 2003 ruled out the use of SOAP encoding with web services. Document/literal and RPC/literal will be the only allowed style/use combinations in the future. |