SOAP is an XML-based protocol for exchanging information between computers. Although SOAP can be used in a variety of messaging systems and can be delivered via a variety of transport protocols, the main focus of SOAP is Remote Procedure Calls (RPC) transported via HTTP. Like XML-RPC, SOAP is platform independent, and therefore enables diverse applications to communicate with one another.
UDDI (Universal Description, Discovery, and Integration) currently represents the discovery layer within the Web services protocol stack.
UDDI was originally created by Microsoft, IBM, and Ariba, and represents a technical specification for publishing and finding businesses and Web services.
At its core, UDDI consists of two parts.
UDDI is a technical specification for building a distributed directory of businesses and Web services. Data is stored within a specific XML format, and the UDDI specification includes API details for searching existing data and publishing new data.
The Web Services Description Language (WSDL) currently represents the service description layer within the Web service protocol stack.
In a nutshell, WSDL is an XML grammar for specifying a public interface for a Web service. This public interface can include the following:
Information on all publicly available functions.
Data type information for all XML messages.
Binding information about the specific transport protocol to be used.
Address information for locating the specified service.
WSDL is not necessarily tied to a specific XML messaging system, but it does include built-in extensions for describing SOAP services.
4. What knowledge needed for Web services client development?
HTML: None, Web Services do not use HTML.
HTTP: How to type in a URL.
SOAP: None to minimal.
WSDL: None to minimal.
XML: None to considerable.
5. What knowledge needed for Web services publishing?
HTML: None, Web Services do not use HTML.
HTTP: How to turn on the 4th Dimension Web server.
SOAP: How to activate 4th Dimension Web Services.
WSDL: None to minimal.
XML: None.
Yes and no. The SOAP and WSDL standards are relatively new, but the idea of sending messages between programs over a network has been around for decades. Past efforts to create network-oriented distributed object frameworks like CORBA, DCOM, and Java RMI haven't gone to waste. While creating these tools, the computer science and application development communities discovered and learned important information about how to
build widely distributed systems. In the words of Tim Bray, co-editor of the XML 1.0 spec:
SOAP has the advantages that it's simpler and easier to implement than any existing alternative, and makes better use of the pervasive Web
infrastructure. The effect is that you can pull a system together using SOAP in weeks, not quarters. Obviously, the alternatives offer richer feature sets, particularly in the area of transaction semantics, security, and so on, but at a dramatically higher cost. SOAP will not sweep all before it; but it will be very widely deployed across the Internet and the intranets of this world.
7. Why are Web services so fashionable?
Today's variety of computer platforms, operating systems, programming languages, and development environments shows no signs of diminishing. Heterogeneity is the norm in the IT world, has always been so, and will remain so for the foreseeable future. Getting diverse systems to communicate and cooperate is an ongoing challenge for many organizations. Past efforts to create an overall framework for network-oriented program integration, such as DCOM and CORBA, are complex, proprietary, and expensive to implement. Reducing the cost and complexity of integration projects is a driving force behind Web Services standardization and adoption. While current Web Service systems have fewer features
than a system like CORBA, today's Web Services offer more features than developers actually need. Fortunately, the largest software vendors in the world, including- Microsoft, IBM, Sun, and Oracle-are cooperating on the core Web Service standards. 4th Dimension's Web Services features enable developers to quickly and easily publish and subscribe to Web Services.
XML-RPC is a protocol that uses XML messages to perform Remote Procedure Calls. Requests are encoded in XML and sent via HTTP POST; XML responses are embedded in the body of the HTTP response.
More succinctly, XML-RPC = HTTP + XML + Remote Procedure Calls.
Because XML-RPC is platform independent, diverse applications can communicate with one another. For example, a Java client can speak XML-RPC to a Perl server.
To get a quick sense of XML-RPC, here is a sample XML-RPC request to a weather service (with the HTTP Headers omitted):
<?xml version="1.0″ encoding="ISO-8859-1″?>
<methodCall>
<methodName>weather.getWeather</methodName>
<params>
<param><value>10016</value></param>
</params>
</methodCall>
The request consists of a simple element, which specifies the method name (getWeather) and any method parameters (zip code).
Here is a sample XML-RPC response from the weather service:
<?xml version="1.0″ encoding="ISO-8859-1″?>
<methodResponse>
<params>
<param>
<value><int>65</int></value>
</param>
</params>
</methodResponse>
The response consists of a single element, which specifies the return value (the current temperature). In this case, the return value is specified as an integer.
In many ways, XML-RPC is much simpler than SOAP, and therefore represents the easiest way to get started with Web services.
The official XML-RPC specification is available at XML-RPC.com. Dozens of XML-RPC implementations are available in Perl, Python, Java, and Ruby. See the XML-RPC home page for a complete list of implementations.
9. What is service discovery Web service protocol stack layer?
This layer is responsible for centralizing services into a common registry, and providing easy publish/find functionality. Currently, service discovery is handled via the UDDI.
Beyond the essentials of XML-RPC, SOAP, WSDL, and UDDI, the Web service protocol stack includes a whole zoo of newer, evolving protocols. These include WSFL (Web Services Flow Language), SOAP-DSIG (SOAP Security Extensions: Digital Signature), and USML (UDDI Search Markup Language). For an overview of these protocols.
10. What is service description Web service protocol stack layer?
This layer is responsible for describing the public interface to a specific Web service. Currently, service description is handled via the WSDL.
