Saturday, November 29, 2008

WSDL and Web Services

As we are in the process of SCI-Flex we always met WSDL(Web Service Descriptive Language) everywhere, Hence I ll do some explanation about WSDL in brief. Since I have already blogged about SOAP, it may be helpful to you as there is an essential interconnectivity between SOAP and WSDL.

WSDL (Web Services Description Language) is an XML-based language for describing Web services and how to access them.As the name implies the WSDL is used to describe the web services, how it is happening is like WSDL is a document written in XML.

The document describes a Web service. It specifies the location of the service and the operations (or methods) the service exposes.The operations and messages are described abstractly, and then bound to a concrete network protocol and message format to define an endpoint. Related concrete endpoints are combined into abstract endpoints (services). WSDL is extensible to allow description of endpoints and their messages regardless of what message formats or network protocols are used to communicate.

It is happy to say that The WSDL 2.0 specification was published as a W3C Recommendation on June 26, 2007.

WSDL Document Structure

A WSDL document is simply a set of definitions. There is a definitions element at the root, and definitions inside. The grammar is as follows:

  • types, which provides data type definitions used to describe the messages exchanged.

  • message, which represents an abstract definition of the data being transmitted. A message consists of logical parts, each of which is associated with a definition within some type system.

  • portType, which is a set of abstract operations. Each operation refers to an input message and output messages.

  • binding, which specifies concrete protocol and data format specifications for the operations and messages defined by a particular portType.

  • port, which specifies an address for a binding, thus defining a single communication endpoint.

  • service, which is used to aggregate a set of related ports.

See an example of WSDL document just to clarify more on what I have told above.

Wednesday, November 12, 2008

Service Oriented Architecture

Greetings everyone,

As Harsha has already given the introduction to CEP, one major aspect of our venture; allow me to drop a few words on the other aspect : Service Oriented Architecture or SOA. Chances are, if you are reading this blog, you'd be well aware of SOA already, so let me sum up on a few important points only.

SOA 101 >>>
Rather than a totally revolutionary concept, SOA can be described as an evolutionary step (and a pretty important one at that) in the path of achieving better reuse in software components. It is a step above from component based software that is geared towards handling more complex issues rising in the world of software systems such as distributed systems, the internet with its multitude of platforms and protocols. 

SOA therefore, in a nutshell is an architecture compromising of different interacting software services, characterized by their loose coupling. The promise of SOA is that the marginal cost involved in the creation of a certain eventual software application will be zero. This is because all the software needed for the functionality of this particular solution already exist (currently servicing other applications) and to make this work, all that is required will be a certain amount of linking and ordering of different services. 

With this promise of low cost, easy solution deployment which is well suited for handling today's complex systems, its not surprising that SOA has become quite popular of late.

SOA & Web Services >>>
If you're thinking now that SOA is just another fancy name for Web Services, well, you're not the only one. While there are many arguments and debates over the theory of Web Services itself or Web Services and SOA; it is generally accepted that Web Services lie at the core of SOA. 

To make things a bit clearer, a Web Service needs two particular conditions to be met; 
  1. All interfaces must be based upon internet protocols (HTTP, SMTP, UDDI)
  2. Messages are passed in XML
Now this is interesting when you consider that in SOA it is required that a service to have a certain platform-independence. This requirement can be fulfilled by XML. Also adding onto this is the fact that protocols such as UDDI, HTML and WSDL are what makes SOA what it is basically. Its therefore not too hard to see the connection between SOA and Web Services and that Web Services can in fact be used to implement a SOA.  

A final word >>>
In today's world of increasing software complexity, SOA rocks! Promoting interconnections among existing IT services, SOA enables a building-block approach to creating cost-effective complex solutions with ease.

Any more questions as to why we are so interested in working with SOA? :)

Wednesday, November 5, 2008

SCI-Flex and Open Source

When planning SCI-Flex, we had to decide on one major factor. That is the development model that we are going to use. We chose Open Source as we believe that it would benefit a larger audience. The SOA and CEP combination being a novel idea is another fact that we believe Open Source will be the best possible way to unleash it's true potential.

The level of research we are expecting to put into this project is immense. However, this doesn't guarantee that the SOA+CEP combination is a true success and does not confirm whether it meets the requirements of a potential user. The Open Source approach gives the SCI-Flex project the ability to be used and utilized in an efficient manner to uncover the true power of CEP systems in the presence of a well organized SOA environment.

Still at the beginning of the project, we have not yet planned about distributions and deployment alternates. Thus, the prime focus remains still in rather What should be done? rather than How should it be done?. As a starting point we've made the source code for SCI-Flex available @ Google Code. You are free to go ahead and give it a try. Further involvement with the project development activities are made possible through the project's mailing lists. Discussions are welcome on the SCI-Flex developer mailing list.

Several Open Source projects such as Apache HTTP Server, Linux Kernel, and Mozilla Firefox have made it the forefront as globally renowned software. We the SCI-Flex project team would like to see someday, our project being a globally renowned software in the SOA+CEP sphere.