relation between two tables/views

hi guys


In my ER diagram i see

table1  arrow  table2

what does the arrow mean ?

thanks
royjaydAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

sdstuberCommented:
assuming the arrow is from table1 to table2

table1 has a many to one relationship with table2

so table2 is likely the parent of table1
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
gnivkorCommented:
that there is a relationship to that table through some sort of constraint, maybe primary / foreign or unique
0
MilleniumaireCommented:
The fact that the line is dotted means the relationship is optional.  The small vertical line through the dotted line implies that the key of table1 (table on the left) is part of the key of table2 (on the right).

I've never seen an ER diagram that uses arrows on the end of the lines and I can only guess that this is suggesting the direction of the relationship, as described by sdstuber.
0
Determine the Perfect Price for Your IT Services

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden with our free interactive tool and use it to determine the right price for your IT services. Download your free eBook now!

DavidSenior Oracle Database AdministratorCommented:
Partial correction to gnivkor above, the relationship is one or more columns in column, commonly called a parent to child relationship.  IOW for any given parent table row, there MAY be one or more child table rows.  Constraints are required to enforce relational integrity -- but they are not required.  

royjayd, here's a reference to explain the different relationships shown by crow's-foot notation:  w2.cs.uregina.ca/~bernatja/crowsfoot.html

HTH,
dvz
0
royjaydAuthor Commented:
My inititial understanding in laymans terms: The table which has primary key (one)  --> maps to table in which that primary key is used as a foreign key (many).
0
DavidSenior Oracle Database AdministratorCommented:
Nods, the parent shares a family name with her/his child(ren).  In this example, there would be a primary (unique) key constraint on the parent, and that value is also stored in each child.  For RI you define a foreign key in the child table, referencing the parent key value.
0
MilleniumaireCommented:
Yes, that is correct in terms of primary and foreign key references.  In terms of the ERD, the many side of the relationship is shown with a "crows foot" and the one side with a single line.
0
royjaydAuthor Commented:
is Many to One relationship just flipping One to Many relationship ? or is there anything extra to it? For example the above arrow can be used to represent Many-to-One and
One-to-Many relationship aswell, right?

thanks
0
sdstuberCommented:
yes

I used the phrase "many to one" based on the direction of the arrow.

but had it been pointing the other way I'd have said "one to many"
0
DavidSenior Oracle Database AdministratorCommented:
Different notations are used for other business rules beyond 1-M, roy.  In your example the bisecting line shows one-or-more.  Replace the "1" line with "0" and (no surprise) it represents zero or more.  The order in which the entities/tables are described may be flipped (sbstuber above, 37867004).

See if this example helps:  a business must have one and only one tax ID number, and a tax ID number is unique to one business.  However, a business must have at least one address; that business MAY have multiple addresses; and an address MAY be used by one or more businesses.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Oracle Database

From novice to tech pro — start learning today.