I was today trying to figure out on working with WebService and found many articles really gospel over the Web Service and its effectiveness in the Market share.
My Questions are:
For a Complex project of critical data, is it better to opt for WebService? What Makes WebService different from other way of fetching the data?
It depends.
Web services can be useful if you need to expose the data across security boundaries, where a direct connection to an RDBMS would be a bad idea.
That mostly depends on the definition of "big thing". My experience with the WS stack and SOAP and all the acronym soup is that it takes an awful lot of workforce to deploy it. The status of the frameworks is complex, and definitely not something a hobbyist can put to work in a couple of afternoons. We have seen how many things on the net became the next big thing just because they were easy. Easy to understand, easy to interact with, easy in technology. Wikipedia, twitter, digg, youtube are internet big things, and they are, from the interaction point of view, light years away from SOAP/WS based interaction. They are KISS: simple and stupid. A whole horizontal market was opened just because of their simplicity. Even multiprocessing platforms like BOINC don't use anything near the WS stack, but they are the core of many high-throughput efforts.
Now, if you have to deal with complex multi-host transactions, authentication, credential delegation, caching... WS is there. It's the target that makes the need: banks, flight reservation, stuff like this. but they won't impact the common programmer. They require too much energy and too many different competences at once to become something usable for a horizontal market of developers.
Also, I am a REST person. I never advocated SOAP with much emphasis, but there was nothing else and it was a better evolution over XMLRPC (which, if you have to perform dumb RPC, IMHO it's still a good choice). Now I changed my mind. You mostly have resources on the web, and you interact with them with HTTP methods. SOAP is nothing but RPC on hypersteroids. No, REST is not the solution that replaces WS. At all. it's simply easier to use and to debug, albeit more difficult to design (you have to think in terms of resources instead of method calls). It's KISS. That's why it has more chances for success on the horizontal market.
Popular method for implementing web services nowdays is to use RESTful API (eg. via Ajax/JSON). It's already "next big thing" – almost every major player has been offering it for years. Google, Flickr, Twitter, you name it.
The answer is... it depends. Web services are not really the next Big thing, they have been a Huge Thing for years now. In business applications, web services allow a big level of interoperability and capabilities never seen before.
They help integration with legacy systems, cooperation between distinct departments, defining loosely coupled interfaces and such. You should read some about Service-oriented architecture.
If all you need is a PHP application that handles data from a single database, you might not need web services at all. If you are designing a solution that revolves around multiple data sources, with complex security involved, multiple languages and/or multiple applications, then web services become essential.
SOAP is a protocol; if working with PHP, you'll need to check out the PHP: SOAP guide to understand how it works. For every language (almost), there are existing APIs to develop web services. Anyhow you might want to check RESTful web services instead of SOAP-based ones, they are generally simpler to implement/understand. But that's another debate ;-).
Cheers.
The big advantage is that they help to implement an API layer.
If you implement your solution using a "bus" where the web services sit, it opens up your product to a far greater range of users and moves away from being a proprietary product.
It also enables people to interface using a wide range of solutions e.g web service clients can be implemented using command line, Jsp, Java, Asp, .NET, PHP etc.
They also enable code re-use e.g. if you implement GetClientDetails (ID) as a web service for one user, when the next group comes along wanting the same thing, all you have to do is give them the WSDL and they are away.