"to be" meaning "should"

[Milanya]

Can anybody give me a link or a good grammatical explanation about usage of the verb "be" meaning "should"?
For example:
What am I to do? = What should I do?
Where is he to go? = Where should he go?
When are they to be there? = Where should they be there?
etc.
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con·text - The part of a text or statement that surrounds a particular word or passage and determines its meaning.

[Arthurivan]

Should is a modal verb. The 'modals' are can, could, may, might, shall, should, will, would, must, have to, have got to, need to, and ought to.

Should is used to express advice. For comparison, must is used to express obligation.

For present and future meanings modal verbs are followed by a verb in its base form-
I might go. The past is much more complicated...

[Milanya]

Thank you, Arthurivan. I already know how to use the verb "should." Now I need a formal explanation how to use "to be" in the same sense.
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con·text - The part of a text or statement that surrounds a particular word or passage and determines its meaning.

[Esl_Expert]

Hello Milanya,

I suspect what you're looking for is "be to". Did you try googling that as a single grammatical unit?

Though "be to" is frequently used to suggest obligation, similar to "must", it is also used with a meaning similar to "supposed to". Many descriptions of "be to" mention the idea that something has been arranged, and that the arrangement results in someone being obligated to do something. That fits your third sentence especially well, I'd say. It also seems pretty applicable to the second sentence. I think your first sentence could reasonably be reworded as "What am I supposed to do?"

I might describe the sentence "What am I to do?" this way:
It can be used to ask literally and directly for instructions, or it can be used more rhetorically to suggest the following idea.
"There is not a good (or better) solution/plan for what to do in this situation, and I doubt that anyone else has a reasonable plan/suggestion/alternative for what to do either."

Here is one link that might interest you:
http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv327.shtml

You can also find a very short description of "be to" here (under the heading "is to/are to"):
http://www.english-test.net/lessons/20/index.html

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“Even death is not to be feared by one who has lived wisely.” ~ Buddha

[Milanya]

Esl_Expert, you are right on the money! Thank you so very much.
_________________
con·text - The part of a text or statement that surrounds a particular word or passage and determines its meaning.