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#1 giggly kisses  Icon User is offline

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Database Modeling

Posted 10 February 2011 - 07:04 PM

Anyone know the difference between a Entity-Relationship Diagram and a relational diagram? I'm doing a homework assignment and its asking me to create a ERD for a database and a relational diagram for a database. I looked through the book and they both look the same.
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Replies To: Database Modeling

#2 June7  Icon User is offline

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Re: Database Modeling

Posted 10 February 2011 - 07:28 PM

Can't your instructor clarify what they are asking for? I don't think anyone here can read minds.
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#3 giggly kisses  Icon User is offline

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Re: Database Modeling

Posted 10 February 2011 - 07:31 PM

View PostJune7, on 10 February 2011 - 07:28 PM, said:

Can't your instructor clarify what they are asking for? I don't think anyone here can read minds.


I'm not asking you to read my mind, I'm asking you what the difference between an ERD and relational diagram is....As it clearly states in the OP.

This post has been edited by giggly kisses: 10 February 2011 - 07:32 PM

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#4 Robin19  Icon User is offline

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Re: Database Modeling

Posted 11 February 2011 - 06:59 AM

Images of ERD's vs. Images of Relational Diagrams

The RD's look like a bunch of blocks. The ERD's have different shapes and sometimes colors. I don't want to give you the answer (and I don't know if I know the right answer), but that should give you a step in the right direction.
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#5 giggly kisses  Icon User is offline

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Re: Database Modeling

Posted 11 February 2011 - 12:10 PM

View PostRobin19, on 11 February 2011 - 06:59 AM, said:

Images of ERD's vs. Images of Relational Diagrams

The RD's look like a bunch of blocks. The ERD's have different shapes and sometimes colors. I don't want to give you the answer (and I don't know if I know the right answer), but that should give you a step in the right direction.


Thanks for the helpful post. Just to clear things up my homework assignment isn't to tell the difference between an ERD or a relational diagram but to actually make them based on a database.
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#6 June7  Icon User is offline

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Re: Database Modeling

Posted 11 February 2011 - 12:47 PM

Can't read the INSTRUCTOR's mind, not yours. If you follow our interpretations which turn out not to be instructor's intent and get an F is it our fault?

This post has been edited by June7: 11 February 2011 - 12:49 PM

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#7 giggly kisses  Icon User is offline

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Re: Database Modeling

Posted 11 February 2011 - 01:06 PM

View PostJune7, on 11 February 2011 - 12:47 PM, said:

Can't read the INSTRUCTOR's mind, not yours. If you follow our interpretations which turn out not to be instructor's intent and get an F is it our fault?


It shouldn't be an interpretation if these are actual database terms with actual definitions. All I'm asking is what the difference is between these two terms.
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#8 June7  Icon User is offline

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Re: Database Modeling

Posted 12 February 2011 - 11:35 AM

Okay, I will take a stab at this. I do not see any technical difference between the definitions of these two terms. The only thing I can imagine your instructor wants is that I have seen ERD refer to a graphical representation of db relationships generated by software designed to produce this graphic model. So again, only your instructor knows for sure. You need more guidance from them on their expectations.

What db app are you using - Access? Access has a utility to define table relationships.

This post has been edited by June7: 12 February 2011 - 11:48 AM

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#9 c#think#:)  Icon User is offline

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Re: Database Modeling

Posted 17 February 2011 - 08:40 AM

Hey!

i know what the difference is, but due to my poor skill of english language it might be a little complicated description, so here goes nothing...

for examlpe... you have table EMPLOYEE with attributes(columns) like EMP_ID, EMP_FNAME, JOB_ID and you have table JOB with attributes like JOB_ID, JOB_DESCRIPTION. Between these tables there is a relation 1:M. Employee can have only one job at a time, and one job can be applied to many different employees. That's why between these tables there is a relation 1:M.

one row in a table represents one entity, the table it self represents a entity set.

Entity-Relationship Diagramm:
Table EMPLOYEE is placed in a box. Just a table(entity set) name without attributes(columns), that's why it is called 'Entity-Relationship'. So, like i said, table EMPLOYEE is placed in a box as well as table JOB(in other box). Between these boxes there is a line(connecting these two boxes/tables/entity sets if you like). Line represents a relationship. In the center of the line there is a rhombus/diamond with verb description of how do JOB relate with EMPLOYEE. In our case it would be something like 'works'. Near EMPLOYEE box should be 'M' it means 'Many', near JOB box shoould be '1' it means one.
That's the Chen Model of ERD. There is also "Bird's paw" Model, but i showed You Chen's model.

Relational Diagram:
Now you put EMPLOYEE in a box a table name and all attributes(columns) vertically. Do the same with JOB box. Draw a line from JOB_ID(primary key of the JOB table) to JOB_ID(foreign key) in EMPLOYEE table.

And there you go!

And remember,
C# Think#
;)
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