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Old February 13th, 2005, 08:06 AM
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Default Help is needed!

Hi all, I am a total newbie to Access. I have just started a course on computing. I am doing an assignment which involves creating a database, using access, for a mountaineering club. In the classroom, we discussed the need to create the Entity Relationship Diagram (ERD) and resolve all the many to manys. I have been using Access for a few days and dont understand the need to create a link table... It is all very confusing for me and i am starting to lose my patience with it all!!! Can anyone help me please, and i would love some tips on how to create a database. Thanks all. Jason
 
Old February 14th, 2005, 08:47 AM
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I know exactly how to get all this done.

Read your course material.

Hope this helps,

:D

mmcdonal
 
Old February 14th, 2005, 11:55 AM
ru1 ru1 is offline
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Hi Jason. Here is a quick explanation about relationships. Think of everything as payroll. There is a Master record with all your information Home address, phone, spouse, children and so on. Now, if you get paid bi monthly, there will be an additional 26 records out there at the end of the year with all your pay records. In addition, if you have COLA and Gas allowance, they will be in that table as well. But there will only be one employee record for you.

This is done because, if we attach all 26 pay records to your master record, then we will use up that amount of space whether or not it is needed. So, if a person leaves part way through the year, we only have 13 records instead of 26. Therefore, the space on the machine is saved.

In addition to space, when you set referential integority, you could not have a pay record for someone who does not have a master record. Therefore, no Widow or Orphen records.

Hope this helps,

RU1

 
Old February 14th, 2005, 03:04 PM
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Jason,
Hang in there, this is a very important concept and how well any database you put together works (or if it does)depends on how you organize it. Learning to analyze the data you are working with and then normalizing can be complex. I'm willing to bet you are NOT the only one in class who is having difficulty with understanding it........ ( I must have gone through at least a dozen books trying to get answers to the "many-to-many" relationship and found only 3 or 4 that even mentioned junction tables. Access Help has a pretty good one.)
Sometimes thinking through several examples and reasons helps ......... The previous responder gave you one, here's another.

You like sports, so think of this:
Start with a league. At ONE INSTANT in time, A league has many teams, a Team has many players, a player plays one position. Create a table to store information that pertains ONLY to the topic of the table (league, team, player, position). With the proper one-to-many or many-to-one relationship you are able to maintain the integrity of your data by restricting what your user can enter (ie: create a list box that contains (and allows)only the entries from your Position table......your users then click on "Pitcher" instead of accidentally entering "pithcer").

This example breaks down quickly when reality hits. We know IN REALITY a player can be on several teams in his or her playing career, so to be useful the design must be further refined to cover the many-to-many relationship (a team has many players, AND a player can be on many teams [in their career]), and in some sports a player may play more than one position (that could have other solutions).

Hope that Helps, and Good Luck.

Loralee






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