What are some of the pitfalls/tips one could give for developing a web service

[shahzeb]

Looking to develop a web service (api) in PHP to offer customers an easier way to integrate with our platform. There are workflow calls that will be validated with user/pass as well as some reporting options.Sorry I can't post more details or code on the subject and I have never developed a web service but have had experience in using them via SOAP.Now I would also need to offer a state or status of the workflow and I think REST would be the best choice here, but still looking for opinions on that.For reporting I would like to offer different options such as XML,Excel/CSV any reason I would pick one over the other?What are some of the pitfalls I should lookout for? What are some gems anyone could offer.Thanks in advance to any help as this is very important for me to understand.UPDATE #1:

• What would be the most secure method?
• What is the most flexible method(Platform independent)

UPDATE #2:a little bit about the data flow. Each user has creds to use the API and no data is shared between users. Usage is submit a request, the request is processed and a return is given. no updates. (Think Google) a search request is made and results are given, but in my case only one result is given. Don't know if this is needed so it's an FYI.