Should I add references for examples? I am writing a paper in Computer Science / Information Technology.  At several points in the paper, I mention the existence of particular types of software products.  For example:


  Advanced web data extraction systems offer the possibility for the user to define and execute Web wrappers by means of interactive graphical users interfaces (GUI) (e.g. Denodo, Kapowtech, Lixto and Mozenda).


The examples I am referencing are commercial products. Some of them have some articles associated with them which I can cite. Should I add reference to these articles? If yes, how can I do that?
Like any other external resources you mention in your paper, in my opinion, the sources for the examples should be listed as regular references. This can happen in various forms:


If there is a scientific paper that in some way presents the external resource, cite that paper.
If the resource is only presented on a website, cite that website like you would cite other web sources. This can take various forms, though you should be consistent within any one paper you write. The author, unless a single person, should probably be the name of the entity that published the resource. The title can either be the website title, or the name of the resource (e.g. software name).


This has various benefits:


All external works are collected in your references section.
If you refer to the same source several times (especially on several pages), you can use the usual mechanisms by placing cite references.
Readers will not get confused by different formats and places for finding external works you refer to.




In an afterthought, I would find it extremely hard to consistently distinguish "examples" from "normal references". By "normal reference", I imagine a paper that confirms a statement you make. Now, imagine a simple statement like


  In past works, users have been provided with feature X.


for which you want to supply a paper that describes a commercial software that does provide feature X. Now, is this paper an "example" or a "normal reference" that serves to confirm your statement? Clearly, it can be seen as both ... which is why I generally advise against trying to distinguish between any such "categories" of cited works.