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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" |
| "concept.dtd"> |
| <concept id="csoap" xml:lang="en-us"> |
| <title>SOAP</title> |
| <shortdesc>SOAP (formerly known as Simple Object Access Protocol) is a lightweight |
| protocol for the exchange of information in a decentralized, distributed environment. |
| A SOAP message is a transmission of information from a sender to a receiver. |
| SOAP messages can be combined to perform request/response patterns. </shortdesc> |
| <prolog><metadata> |
| <keywords><indexterm>SOAP<indexterm>overview</indexterm></indexterm> |
| <indexterm>Web services<indexterm>SOAP</indexterm></indexterm> |
| </keywords> |
| </metadata></prolog> |
| <conbody> |
| <p>SOAP is transport independent but is most commonly carried over HTTP in |
| order to run with the existing Internet infrastructure. SOAP enables |
| the binding and usage of discovered Web services by defining a message path |
| for routing messages. SOAP is used to query UDDI for Web services. The workbench |
| supports SOAP 1.1.</p> |
| <p>SOAP is an XML-based protocol that defines three parts to every message:</p> |
| <ul> |
| <li> <uicontrol>Envelope.</uicontrol> The envelope defines a framework |
| for describing what is in a message and how to process it. A SOAP message |
| is an envelope containing zero or more headers and exactly one body. |
| The envelope is the top element of the XML document, providing a container |
| for control information, the address of a message, and the message itself. |
| Headers transport any control information such as quality-of-service attributes. |
| The body contains the message identification and its parameters. Both |
| the headers and the body are child elements of the envelope.</li> |
| <li> <uicontrol>Encoding rules.</uicontrol> The set of encoding rules |
| expresses instances of application-defined data types. Encoding rules define |
| a serialization mechanism that can be used to exchange instances of application-defined |
| data types. SOAP defines a programming language-independent data type scheme |
| based on XSD plus encoding rules for all data types defined according to this |
| model. SOAP encoding is not WS-I compliant and thus the Literal use (which |
| is no encoding) is suggested for interoperable Web services and required for |
| WS-I compliance.</li> |
| <li> <uicontrol>Communication styles.</uicontrol> Communications can follow |
| a remote procedure call (RPC) or message-oriented (Document) format. |
| These are discussed below.</li> |
| </ul> |
| <section><title>Binding styles</title><p>SOAP supports two different communication |
| styles:</p><lq> <p> <uicontrol>Remote procedure call (RPC):</uicontrol> |
| Invocation of an operation returning a result. Typically used with SOAP encoding, |
| which is not WS-I compliant.</p><p> <uicontrol>Document Style:</uicontrol> |
| Also known as document-oriented or message-oriented style. This style |
| provides a lower layer of abstraction, and requires more programming work.</p> </lq></section> |
| <section><title>Encoding styles</title><p>In distributed computing environments, |
| encoding styles define how data values defined in the application can be translated |
| to and from a particular protocol format. The translation process is |
| know as serialization and deserialization.</p><p>The SOAP specification defines |
| the SOAP encoding style:</p><lq> <p> <uicontrol>SOAP encoding:</uicontrol> |
| The SOAP encoding style allows you to serialize/deserialize values of data |
| types from the SOAP data model. This encoding style is defined in the |
| SOAP 1.1 standard, and is not WS-I compliant.</p> </lq><p>WSDL defines the |
| Literal XML encoding style:</p><lq> <p> <uicontrol>Literal XML:</uicontrol> |
| Literal refers to the fact that the document should be read as-is, or unencoded. |
| The document is serialized as XMI, meaning that the message XML complies with |
| the Schema in the WSDL. When using Literal encoding, each message part references |
| a concrete schema definition. Literal encoding is WS-I compliant.</p> </lq></section> |
| <section><title>Data model</title><p>The purpose of the SOAP data model is |
| to provide a language-independent abstraction for data types used by common |
| programming language types. It consists of:</p><ul> |
| <li> <uicontrol>Simple XSD types.</uicontrol> For example int, string, |
| and date.</li> |
| <li> <uicontrol>Compound types.</uicontrol> There are two kinds of compound |
| types, <varname>structs</varname> and <varname>arrays</varname>. Structs |
| are named aggregate types in which each element has a unique name or XML tag. |
| Arrays have elements that are identified by position, not by name.</li> |
| </ul><p>All elements and identifiers comprising the SOAP data model are defined |
| in the namespace URI. The SOAP standard defines the rules for how data |
| types can be constructed. A project specific XML schema must define the actual |
| data types. The elements of the SOAP specification are defined in <xref format="html" |
| href="http://schemas.xmlsoap.org/soap/envelope/" scope="external">http://schemas.xmlsoap.org/soap/envelope/</xref> and |
| <xref format="html" href="http://schemas.xmlsoap.org/soap/encoding/" scope="external">http://schemas.xmlsoap.org/soap/encoding/</xref></p></section> |
| <section><title>SOAP implementations</title><p>Different implementations of |
| the SOAP protocol are available today. For example, the Apache Foundation |
| provides Apache SOAP, which grew out of an <tm tmclass="ibm" tmowner="IBM Corporation" |
| tmtype="reg" trademark="IBM">IBM</tm> project called SOAP4J, as well as Apache |
| Axis and the <tm tmclass="ibm" tmowner="IBM Corporation" tmtype="reg" trademark="IBM">IBM</tm> <tm |
| tmclass="ibm" tmowner="IBM Corporation" tmtype="reg" trademark="WebSphere">WebSphere</tm> run-time |
| environment. The provided Web services tools support Apache SOAP 2.3, Axis |
| 1.3, and <tm tmclass="ibm" tmowner="IBM Corporation" tmtype="reg" trademark="IBM">IBM</tm> <tm |
| tmclass="ibm" tmowner="IBM Corporation" tmtype="reg" trademark="WebSphere">WebSphere</tm> implementations.</p></section> |
| <section><title>Mappings</title><p>A mapping defines an association between |
| a qualified XML element name, a <tm tmclass="special" tmowner="Sun Microsystems, Inc." |
| tmtype="tm" trademark="Java">Java</tm> class name, and an encoding style. |
| The mapping specifies how, under the given encoding, an incoming XML element |
| with a fully qualified name is converted to a <tm tmclass="special" tmowner="Sun Microsystems, Inc." |
| tmtype="tm" trademark="Java">Java</tm> class and vice versa.</p><p>For more |
| information on Apache SOAP, refer to <xref format="html" href="http://xml.apache.org/soap" |
| scope="external">xml.apache.org/soap</xref> For more information on |
| SOAP refer to <xref format="html" href="http://www.w3.org/TR/SOAP" scope="external">www.w3.org/TR/SOAP</xref> </p></section> |
| </conbody> |
| <related-links> |
| <linklist><title>Related Concepts</title> |
| <link href="cws.dita"><linktext>Web services overview</linktext></link> |
| <link href="cwsinwsa.dita"><linktext>Tools for Web services development</linktext> |
| </link> |
| </linklist> |
| <linklist><title>Related Tasks</title> |
| <link href="../tasks/toverws.dita" scope="peer"><linktext> Developing Web |
| services</linktext></link> |
| </linklist> |
| </related-links> |
| </concept> |
