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..
asked Dec 17, 2011 at 08:37 AM in Default
OK, so a brief run-down of ER diagrams would be:
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.
answered Dec 23, 2011 at 05:56 AM