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Simple Object Access Protocol Overview

This chapter provides an overview of the Simple Object Access Protocol (SOAP), and includes a description of the architecture of the Oracle SOAP implementation.

This chapter covers the following topics:

What Is the Simple Object Access Protocol?

The Simple Object Access Protocol (SOAP) is a lightweight, XML-based protocol for exchanging information in a decentralized, distributed environment. By combining SOAP-based requests and responses with a transport protocol, such as HTTP, the Internet becomes a medium for applications to publish database-backed Web services, such as:

Restaurant listings: Which sushi bars are within five blocks of the Geary Theatre?
Car dealer inquiries: What California dealers have a denim blue Audi TT coupe in stock?
Financial information requests: What stocks in my portfolio are below their 50-day average?
Ticket bookings: What are the two best seats available for Miss Saigon next week?

SOAP has a looser coupling between the client and the server than some similar distributed computing protocols, such as CORBA/IIOP, and it provides easier communication for a client and server that use different languages. SOAP exposes a standard way for processes to communicate, yet it leverages existing technologies.

SOAP requests are easy to generate, and a client can easily process the responses. One application can become a programmatic client of another application's services, with each exchanging rich, structured information. The ability to aggregate powerful, distributed Web services allows SOAP to provide a robust programming model that turns the Internet into an application development platform.

SOAP has the following features:

Protocol independence
Language independence
Platform and operating system independence

See Also:

http://www.w3.org/TR/SOAP for information on Simple Object Access Protocol (SOAP) 1.1 specification

How Does SOAP Work?

The SOAP specification describes a standard, XML-based way to encode requests and responses, including:

Requests to invoke a method on a service, including in parameters
Responses from a service method, including return value and out parameters
Errors from a service

SOAP describes the structure and data types of message payloads by using the emerging W3C XML Schema standard issued by the World Wide Web Consortium (W3C). SOAP is a transport-agnostic messaging system; SOAP requests and responses travel using HTTP, HTTPS, or some other transport mechanism.

Figure 1-1 illustrates the components in the SOAP architecture. In general, a SOAP service remote procedure call (RPC) request/response sequence includes the following steps:

A SOAP client formulates a request for a service. This involves creating a conforming XML document, either explicitly or using Oracle SOAP client API.
A SOAP client sends the XML document to a SOAP server. This SOAP request is posted using HTTP or HTTPS to a SOAP Request Handler running as a servlet on a Web server. Example 1-1 shows the body of a SOAP message, an XML document, that represents a SOAP request for a service that provides an address from an address book.
The Web server receives the SOAP message, an XML document, using the SOAP Request Handler Servlet. The server then dispatches the message as a service invocation to an appropriate server-side application providing the requested service.
A response from the service is returned to the SOAP Request Handler Servlet and then to the caller using the standard SOAP XML payload format. Example 1-2 contains the body of a response to the request made in Example 1-1.

See Also:

http://www.w3.org/TR/SOAP
http://www.w3.org/XML/Schema for information on XML Schema

Figure 1-1 Components of the SOAP Architecture

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The SOAP specification does not describe how the SOAP server should handle the content of the SOAP message body. The content of the body may be handed to a SOAP service, depending on the SOAP server implementation.

Example 1-1 SOAP Request for Address Book Listing Service

<SOAP-ENV:Envelope 
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" 
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" 
xmlns:xsd="http://www.w3.org/1999/XMLSchema">
<SOAP-ENV:Body>
<ns1:getAddressFromName xmlns:ns1="urn:www-oracle-com:AddressBook" 
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" 
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
<nameToLookup xsi:type="xsd:string" xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance">
John B. Good
</nameToLookup>
</ns1:getAddressFromName>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Example 1-2 SOAP Response from Address Book Service

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" 
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" 
xmlns:xsd="http://www.w3.org/1999/XMLSchema">
<SOAP-ENV:Body>
<ns1:getAddressFromNameResponse xmlns:ns1="urn:www-oracle-com:AddressBook" 
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<return xmlns:ns2="urn:xml-soap-address-demo" xsi:type="ns2:address">
<city xsi:type="xsd:string">Anytown
</city>
<state xsi:type="xsd:string">NY
</state>
<phoneNumber xsi:type="ns2:phone">
<areaCode xsi:type="xsd:int">123
</areaCode>
<number xsi:type="xsd:string">7890
</number>
<exchange xsi:type="xsd:string">456
</exchange>
</phoneNumber>
<streetName xsi:type="xsd:string">Main Street
</streetName>
<zip xsi:type="xsd:int">12345</zip>
<streetNum xsi:type="xsd:int">123
</streetNum>
</return>
</ns1:getAddressFromNameResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Why Use SOAP?

Why do we need a standard like SOAP? By exchanging XML documents over HTTP, two programs can exchange rich, structured information without the introduction of an additional standard such as SOAP to explicitly describe a message envelope format and a way to encode structured content.

SOAP provides a standard so that developers do not have to invent a custom XML message format for every service they want to make available. Given the signature of the service method to be invoked, the SOAP specification prescribes an unambiguous XML message format. Any developer familiar with the SOAP specification, working in any programming language, can formulate a correct SOAP XML request for a particular service and understand the response from the service by obtaining the following service details.

Service name
Method names implemented by the service
Method signature of each method
Address of the service implementation (expressed as a URI)

Using SOAP streamlines the process for exposing an existing software component as a Web service since the method signature of the service identifies the XML document structure used for both the request and the response.

See Also:

http://www.w3.org/Addressing for information on URIs, naming, and addressing

What Is Oracle SOAP?

Oracle SOAP is an implementation of the Simple Object Access Protocol. Oracle SOAP is based on the SOAP open source implementation developed by the Apache Software Foundation.

This section describes the Oracle SOAP components shown in Figure 1-2. The topics covered include:

Figure 1-2 Oracle SOAP Architecture

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Client Application and Client API

A SOAP client application represents a user-written application that makes SOAP requests. A SOAP client application may include the following:

SOAP Client API

SOAP clients generate the XML documents that compose a request for a SOAP service and handle the SOAP response. Oracle SOAP processes requests from any client that sends a valid SOAP request. To facilitate client development, Oracle SOAP includes a SOAP client API that provides a generic way to invoke a SOAP service. The SOAP client API supports a synchronous invocation model for requests and responses.

The SOAP client API makes it easier for you to write a Java client application to make a SOAP request. The SOAP client API encapsulates the creation of the SOAP request and the details of sending the request over the underlying transport protocol. The SOAP client API also supports a pluggable transport, allowing the client to easily change the transport (available transports include HTTP and HTTPS).

Oracle SOAP Security Features

Oracle SOAP uses the security capabilities in the transport to support secure access and to support other security features. For example, using HTTPS, Oracle SOAP provides confidentiality, authentication, and integrity over the Secure Sockets Layer (SSL). Other security features such as logging and authorization, are provided by the service provider.

SOAP Transports

SOAP transports are the protocols that carry SOAP messages. Oracle SOAP supports the following transports:

HTTP: This protocol is the basic SOAP transport. The Oracle SOAP Request Handler Servlet manages HTTP requests and supplies responses directly over HTTP.
HTTPS: The Oracle SOAP Request Handler Servlet manages HTTPS requests and supplies responses, with different security levels supported.

Administrative Clients

SOAP administrative clients include the Service Manager and the Provider Manager. These administrative clients are services that support dynamic deployment of new services and new providers.

SOAP Request Handler

The SOAP Request Handler is a Java servlet that receives SOAP requests, looks up the appropriate service provider, handles the service provider that invokes the requested method (service), and returns the SOAP response, if any.

SOAP Provider Interface and Providers

Oracle SOAP includes a provider implementation for Java classes. Other providers can be added.

Provider Interface

The provider interface allows the SOAP server to uniformly invoke service methods regardless of the type of provider (Java class, stored procedure, or some other provider type). There is one provider interface implementation for each type of service provider, and it encapsulates all provider-specific information. The provider interface makes SOAP implementation easily extensible to support new types of service providers.

Provider Deployment Administration

Oracle SOAP provides the provider deployment administration client to manage provider deployment information.

SOAP Services

SOAP application developers provide SOAP services. These services are made available using the supplied default Java class provider or custom providers. Oracle SOAP includes a service deployment administration client that runs as a service to manage services.

SOAP services, including Java services, represent user-written applications that are provided to remote SOAP clients.

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