One of the items that needed a further
development was a research on child
nodes of a story representing its sub
categories being updated the moment
the list of sub categories is changed
through edit page for stories.
While this sentence looks grammatically correct, it is too long to be clearly understood. It is possible to split it in shorter sentences and keep the same meaning. That's what I recommend. For example:
One of the items that needed further
development relates to the child
nodes. The child nodes represent the
subcategories of a story. They need
to be updated when the subcategory
list is changed via the Edit page for
stories.
To answer your questions about that sentence:
Is my usage of passive voice (being updated) to describe what this
research was about correct?
I don't think it was wrong, but it wasn't very clear.
What other options (all you can think
of) are possible? How do they change
the meaning
See if you like the change that I made in the sentences above on the clause that included "being updated".
The short answer is that you may employ the simple past perfect to express a continuing action only when the expression is atelic or bears in context a reasonably natural atelic interpretation.
A telic expression is one which has a goal or ending point "built in" to its sense—finish, for instance. Employing the test suggested in the article linked above, it makes perfect sense to say He finished in an hour, but not (normally) He finished for an hour.
Expressions which do not have such a goal are atelic. In your first example, work is an atelic expression: using the same test, He worked for an hour is acceptable, but not (normally) He worked in an hour. Atelic expressions are, so to speak, inherently continuous. Consequently, a simple past perfect construction use supports a continuous sense; this is why the two are "interchangeable".
Your other examples, however, are telic. Eating dinner and cleaning a room are not (normally) protracted indefinitely, they come to an end when the dinner is consumed and the room is clean. Consequently, using simple perfect constructions implies completion, and if you want to convey that the action continues you must employ a progressive construction.
Note, however, that "telicity" is a very subtle matter in practice. As the linked article tells you, grammarians are in some disagreement over just how it works; and I have been careful to qualify all my analyses with the (normally) tag.
Note, too, that there is an alternative to the two constructions you illustrate. The past progressive ("I was eating dinner when ... " and "I was cleaning my space when ... ") is more natural to my ear than the past perfect progressive. You want the past perfect progressive only if you employ a qualifier like since dawn, which removes the focus from the present-in-the-past to the past-in-the-past, the stretch of time which preceded the present-in-the-past.
Best Answer
In the first example, the comma feels necessary because you're connecting two independent clauses, not because you're repeating the subject.
The two clauses, "Nokia is not your favorite brand" and "it is the best in my opinion," both can stand alone grammatically as simple sentences. This is what makes them independent clauses.
In school, I learned the "comma FANBOY rule" (For And Nor But OR Yet), it's the first comma rule in this guide:
https://owl.english.purdue.edu/owl/resource/607/02/
However, when the two clauses are well balanced, I'd say it's pretty common and widely accepted to leave this comma out. Because of this, I've heard someone call the FANBOY rule a pseudorule.
In your first example, the two phrases aren't well balanced in my opinion. The word is without a subject feels really jarring, even though it is grammatically equivalent to the word are in your second example.