Query is based on Webservices on XML

I am new to Web Service and XML
Just got a job from a client that wants me to build a web app that does what is listed below and other stuff. The scripting language is PHP 5.3

Admin create, modify and delete user
Admin view user details
User login and view their details

At the end of the mail sent to me are 3 information which are listed below
The Query is based on Webservices on XML
The backend Database to be MYSQL
The Operating system to be Cent OS 6.1

I work with MySQL and Google search has shown me that Cent OS is a flavour of Linux but the problem is that I do not understand the term ‘The Query is based on Webservices on XML’. I have google for XML and I think it is a technology I can work it. But I did not see any connection about issuing a query inside XML. Please can anybody help out with the term “The Query is based on Webservices on XML” so that I can have an intelligent discussion with client when next I meet with him.

I guessing that by “webservices on XML” they mean either “SOAP” and/or “REST”.
There are PHP SOAP functions that could help make things easier for you.
And there are PEAR packages for both SOAP and REST

Thank you let me go get books and read up. Please are SOAP and REST are also a technology for exchanging data between platform

Yes, the idea is that by using XML any language that can work with XML can interact with the web service.

Which of the two (or other methods eg. JSON) is better is open to debate.
But I guess a lot depends on how much control and data integrity you need to enforce.
eg. a required parameter, integer 1 and not string one, etc.

Thank you I think I am now knowledgeable to discuss with my client about web service now.