Consider a conference publishing papers related to any EC/CS engineering field. What is the exact difference between different types of papers published in such a conference, i.e., main conference paper, mini-conference paper and workshop paper? Is it inferior to have one's work published in a mini-conference or workshop as opposed to a full conference? Are there any other such sessions within usual conferences for these areas?
For the value of the publication, it will matter more how it is published than whether it's a workshop or conference. If the proceedings are published by a well-known publisher (i.e. with ISBN/ISSN), a workshop paper might be as "valuable" as a conference paper. If on the other hand there are no formal proceedings or just something like a folder, it would be less "valuable". That usually leaves the opportunity to publish the same paper elsewhere though.
Most workshops in CS don't have formal proceedings, so in general it would be better to publish at a conference. That said, in some cases the reviewing process for a workshop/symposium might be more stringent. As smaller events are more specialised, the feedback you get on your work might be better than at a bigger event.
I personally would always go for publication at a conference if I thought the content of the paper to be good enough.
Miniconferences and workshops are usually considered to be satellite events to a main conference. Often, these are on specialized topics, and often what starts as a workshop becomes a spin off conference of its own.
So it's tricky to say that it's inferior, but depending on the workshop/miniconference it might certainly be more specialized.
I agree with everything that has been said so far, but I'd like to add that one way to more quantitatively judge the "value" of a publication is by looking at the acceptance rate of the venue. Many conferences in Computer Science are considered "terminal" publications because of their extremely competitive nature and low acceptance rates. There are other conferences, however, that have 50% or higher acceptance rates. Likewise, some workshops are very competitive while others have near 100% acceptance rates.