When should a web service not be used?

Question

Using a web service is often an excellent architectural approach. And, with the advent of WCF in .Net, it\'s getting even better.

But, in my experience, some people

Answer 1

For a small-scale web app (You have to ask the question, "Will it always remain small scale?" though) using web services, separate business layers, data layers, and so on and so forth can be overkill.

Before anyone shoots me, I do agree that separation of logic between layers along with unit tests, continuous integration, et al are bloody brilliant. In my current role I'd be utterly lost and rocking in the corner without them. However for a very small-scale web app being used to, for example, track contact numbers and addresses for a company of 36 employees, the cost/benefit analysis would suggest that all the "niceties" listed above would be overkill.

However... Remember to ask the question "Will it always remain small scale?" :-)

Answer 2

Just because the tool generates a bunch of stubs doesn't mean it's a good use. WS-* excels in scenarios where you expose services to external parties. This means that each operation should be on the granularity of business process as opposed to data access.

The multitude of standards can be used to describe different facets of your contract in great detail and a (hypothetical) fully compliant WS stack can take away a lot of pain from the third party developers and even allow the fabled point and click integration a'la Yahoo Pipes. With good governance controls you can evolve your public interface and manage the backward compatibility as needed.

All this is next to impossible to be generated automatically. The C# stub generator knows only the physical interface of your class, but doesn't have any idea about the semantics involved. See this paper for more detailed discussion.

If you are building a web site, then build a web site. If you want asynchronous messaging inside your application, use MSMQ. If you want to expose data to internal clients, use POX. If you need efficient binary message format, check Google's Protocol Buffers or if you need RPC check Hessian for C# or DCOM.

Web services are a coarse grained integration solution. They are rigid, they are slower than alternatives, they take too much effort to do well (and when not done well are next to pointless).

To summarize: "When should a web service not be used?" - anytime you can get away without it

Answer 3

If you are just coding a tiny (less than 50 users) web application for your intranet, a web service seems overkill. Especially if its primary function (providing a single point of access to many services) won't be used.

Answer 4

Nick Harrison, a brilliant developer in Charlotte, suggested these scenarios where using a web service makes sense:

• On a Web farm, where there are multiple web servers hosting website(s), all pointing to web service(s) running on another web server. This allows for distributing the load over multiple servers.
• Client/server, where Windows forms apps can call a web service.
• Cross platform
• Passing through a firewall

Answer 5

For a small scale web app I think that using web services is often quite a good idea, you can use it to easily decouple the web server from the data tier. With the straightofrward development requirements and great tooling I don't see the problem.

However don't use web services in the following scenarios:

• When you must use Http as the transport and Xml serialization of your data and you need lots of different bits of data, synchronously and often. Whether REST or SOAP or WS-* you're going to suffer performance issues. The more calls you make the slower your system will be. If you want medium size chunks of data less frequently, asynchronously and you can use straight TcpIp (e.g. Wcf netTcpBinding) you'd be better off.
• When you need to query and join data from your web service with other data sources, rather motivate for a data warehouse which can be populated with properly consolidated and rationalized data from across the enterprize

This is my experience, hope it helps.

Answer 6

I agree that the use of a web service in a small scale web app adds a layer of complexity that does not seem justified. Most of my solutions, internet and intranet, 10-50 users, do not employ web services. I am glad others feel the same...I thought I was the only one.