Web service in CMS such as DSpace, Moodle, EPrints, WordPress, Joomla, Open Journal System?

Hi I am a college student and a newbie in web service. I did some research about web services however, and I am going to add a web service to some websites in my institute to integrate data from them. Since they are various CMS (like I mentioned in the title), I need info about them. What I ask about is the **features, advantages and disadvantages** (and maybe the requirements needed) about web services in each of the CMS (DSpace, Moodle, EPrints, WordPress, Joomla, Open Journal System)... for example, if I’m not mistaken, WordPress provides web services like RSS. Do the others provide it too? Sorry for the vague question, but I really have no idea - especially about **DSpace, Moodle, OJS and EPrints** - any information would be helpful.