Creating ER charts

[TipGiver]

Hi,
this is a basic question. We have:
- line
- line with arrow
- strong line
- strong line with arrow

Also:
- 1 to 1
- 1 to many
- many to 1
- many to many

What is the relationship between those and the lines?
For example: There is a program to work with. One or more members can take part in.

Thank you.

 

[TipGiver]

I think that the relationship is:

- line : many to many
- line with arrow : many to 1
- strong line : 1 to many
- strong line with arrow : 1 to 1


Do you agree?

 

[alvechurchdata]

I'd interpret a plain line as being one-to-one.

Wherre are you seeing these lines? Is it in an ER diagram being produced by some database design software?

Geoff Franklin

http://www.alvechurchdata.co.uk

 

[TipGiver]

I create an ER diagram with entities, attributes and relationships. I have written down on a paper sentences like: A student has: name, age, semester ...etc. The proffessor has ... This lesson is being taken by many students. Only one proffessor is teaching it.
Etc.

I will create these sentances into a diagram using MS Visio.

 

[ceh4702]

One simple way is to use box for an object and a diamond for a relationship and inside the diamond what the relationship is. Then put 1 or M next to the box.

There is another way to write the relationship on both sides of the line and then use straight lines and crows feet which is more exact. A lot depends if you are Data Modeling which is not at the Logical level or actually doing an ER which is suppose to be at the physical level. If you can get some software to do this it might be easier.

There is some software that is shareware like SmartDraw. I think MS makes some diagram software that is really expensive also.

This is an example

http://www.smartdraw.com/examples/software-erd/hospital_billing_system.htm

If you do not like my post feel free to point out your opinion or my errors.

 

[TipGiver]

One simple way is to use box for an object and a diamond for a relationship and inside the diamond what the relationship is. Then put 1 or M next to the box"

You are right!

Look at this:

BOX DIAMOND BOX
teacher works_in school
-ssn
-name
-age
(attributes)


I have to connect the box with the diamond, and the diamond with the last box (right?). The ways are:

------- this and the next have lineweight one
------>
======= this and the next have lineweight five
======>