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Publication Date: 2010-Sep-22
Document File: 3 page(s) / 81K

Publishing Venue

The Prior Art Database


The publication discloses an enhancement to existing Web Service Description Language (WSDL) for events subscriptions. The "porttype" element in WSDL contains a set of "operation" elements available for the clients to make calls. This "porttype" element is improved upon to contain "callback" elements similar to "operation" that lists the available service events which the client can subscribe to. With this enhancement, any client to a web service is allowed to subscribe to the server events defined in the WSDL. The service implementation would then callback the client when the specific event occurs. Polling the server for state changes can be completely eliminated with this mechanism. Additionally, the article also discusses on the implementation feasibility of the invention disclosure.

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The ability of a software service to inter-communicate with its independent peers makes it a potential candidate for a Service Oriented Architecture (SOA) implementation. In modern software solutions, this ability to interface with other software services is seen as a mandatory requirement. Web service is one of the widely used communication mechanisms that allows independent, heterogeneous software systems to inter-communicate. Web Service Description Language (WSDL) is the standard interface definition language used by service providers to expose their set of services. It is an XML based language that provides a model for describing Web services. It contains details such as service, port type, operation, binding among others which aids any client to discover the service and make appropriate RPC calls.

This publication aims at providing an additional feature to WSDL that will allow clients to subscribe to server events. Every call in a web service communication, whether synchronous or asynchronous, is initiated by the client. This is due to the fact that the current web service standards do not define a mechanism for events subscription. With the current implementation of web service, the client needs to periodically poll the server for identifying state changes on the server. Many a time, no action is taken at all in polling mechanism because either no data is available for processing or the expected state change has not occurred on the server. The callback mechanism discussed in this article is nothing new to the software industry. It existed from the days when function pointers were introduced in the C language. In this article we discuss on how event subscriptions and callbacks can be introduced into the web service standard thereby making life easy for programmers of distributed computing.

The problem statement is best explained with an example. Consider an integrated trading platform for financial markets that contains a dashboard for monitoring


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customers, foreign exchange and derivative positions among others. Consider that the server applications expose their interfaces in the form of web services. To display the latest/updated information, the dashboard application has to periodically poll the server(s) with appropriate API calls. In the above scenario, if the dashboard application can subscribe to events such as "foreign exchange rate change", "arrival of new quotes", "derivative position change" ..., it will make its work easier/cleaner. Moreover, the client will be able to display the latest possible (near-live) data on the dashboard because the client method will be triggered as and when the data arrives. Minimal client-server communication leads to reduced burden on network/hardware.

Implementation feasibility

The reference section contains links to articles that discusses on various

implementations of asynchronous web service calls. Leveragin...