ER Diagram(CDM)

[smiley4080]

Can anyone help me in this Question .
found the entity type and the constraint , limitation, assumption and diagram

Represent part of the mlitary command structure of the armies of 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 90,000 - 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 think that entity type is :
country
army
field

I think the attribute of countru is the name and the primary key is code >> what you said

country( countryCode, countryName)

so the entity and there attribute but i am not sure it's correct

country : name , code , army name
Army (army name , country name , field army )
- field army : solders number , field army name , army name
- Solders : name , ID , rank
- General : army name , field army name ,
- Marshall : army name , ID , filed army name
- commander – in chief: name ,ID , army name , country name

So please if any one can help me??

[debasisdas]

country : country_code ,country_name
Army : army_code, army_name , country_code
Solders : name , ID , rank,country_code

[smiley4080]

Thanks a lot debasisdas for your reply
is helpful :$

[smiley4080]

country : country_code ,country_name
Army : army_code, army_name , country_code
Solders : name , ID , rank,country_code

why army entity not included the rank
Country(CountryName, Country Code )
Army (ArmyID, name,rank , Country Code)

[debasisdas]

My understanding is army does not have a rank a soldier has.

[mlesniak]

It looks to me like the country and army are one entity: you can't have an army without a country and you can't have a country without an army.
One country's army may have one or many 'Field Armies'.
General must be an entity because not all generals head a Field Army, but all Field Armies must have a General. Therefore each General may head one or no Field Army.
Field Marshall can be a property of a Country/Army because there is a one to one relationship between them.
I guess that Soldier must be an entity if information about each individual soldier needs to be stored (if not then the number of soldiers can be a property of Field Army). If Soldier is made an entity then the relationship between Soldier and Field Army must be such that a minimum of 90,000 and a maximum of 200,000 Soldiers may be related to any single Field Army.
NOTE: there are diagramming tools to describe the entity relationships, such as Violet which is a free Java written tool. If you have Microsoft Visio then that will be a good one too.

[smiley4080]

I think Soldier, Marshall, Commander etc. are roles so that They are not entities.