help in ER-Diagram

this is the scenario

Represent part of the military command structure of the armies of the world. It is desired to represent every command unit and all army personnel, along with their ranks and personal details. Each country has one army who has a Commander-In-Chief. Each army is divided into a number of field armies. Each field army has between 80,000 - 200,000 soldiers and is headed by a General. There is only one Field Marshall in each army. Not all generals head a field army.

I becoming confuses.. I don't now which is the entity .. first I think is Army , country , Field but I am not sure .. can anyone help me..
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asked Dec 17, 2011 at 08:37 AM in Default

sun 1 gravatar image

sun 1
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Well, he has actually tagged it as homework. I'll answer it if I get the certificate!
Dec 17, 2011 at 09:52 AM Phil Factor
Will you handle multi-national peace-keeping forces?
Dec 17, 2011 at 10:51 AM Raj More
From your questions, it seems like you're embarking on something more complex than mere database design. Seems like Enterprise Architecture to me.
Dec 17, 2011 at 10:54 AM Raj More

I agree with you and I know it is homework but I need some help from professional because I recently take the courses ( distance learning student ) and I solve it but I am not sure its correct so I need some opinion or idea that might help me..

Hint: First in my answer I think the entities are Country , Army , FieldArmy but then I found out that may the country and army are one entity because you can't have an army without a country and you can't have a country without an army. also, I think a Commander-In-Chief, soldiers ,General,Marshall are all army rank so that I think it is not entity..

Dec 18, 2011 at 08:04 AM sun 1
Everyone - we support homework questions on this forum by offering suggestions on where to get answers and how to research the information needed. We don't (sadly) get any more credit for it than for helping with other questions.
Dec 19, 2011 at 12:55 PM Fatherjack ♦♦
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OK, so a brief run-down of ER diagrams would be:

  • Entities - these are things (
  • Attributes - these are properties of the things
  • Relationships - these are what link things together

Print out the scenario, grab a highlighter, and start reading. Underline nouns, as they are potential entities or attributes of those entities.

Look for phrases such as "each foo has a bar" - that indicates a potential relationship or an attribute. If there's guaranteed to be one and only one bar in a foo, then you could make it an attribute of the foo, otherwise you might want to set up a separate bar table, and then create a linking table for "foobar" that links the foo ID to none, one or many bar IDs. (If it helps, try replacing "foo" with "hotel" or "town" in this paragraph!)

Have a quick read of http://en.wikipedia.org/wiki/Entity-relationship_model - it may help.
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answered Dec 23, 2011 at 05:56 AM

ThomasRushton gravatar image

ThomasRushton ♦
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asked: Dec 17, 2011 at 08:37 AM

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Last Updated: Dec 17, 2011 at 08:37 AM