Correct! A table … Correct! A table in the physical db is equivalent to an Entity in the LDM. A column within that table is equivalent to an Attribute in the LDM.
An instance of … An instance of recorded data — an actual record of information composed of one or more columns within a table — becomes a row within the physical database schema.
When first learning … When first learning about logical data modeling, it is common to confuse the definition of data structure with the instances of the data itself. Actually, the data elements that were referring to here are often called attributes. An attribute in the logical data model will become a column in the physical implementation of a table within a database schema.
That’s correct; the … That’s correct; the data elements that repeat — those that potentially will have multiple instances — are segregated into a separate entity. The relationship among these entities is driven by propagation of the foreign key from the main entity to the subordinate entity (from the parent entity to the child entity).
so I think you mean … so I think you mean that you cant have attributes with more than one occurance. Like people cant have more than one name, but they can have more than one item that they are ordering. So then a seperate entity for items would need to be made with a relationship to the order?
Don’t confuse the … Don’t confuse the definition of attributes with the instance of values within the materialized table once you’ve actually created a table based on the logical data model. Remember that Entities are to tables as Attributes are to Columns.
so that means that … so that means that a different entity instance cant have any of the same non key attributes. So if there was the customer name attribute, there could be two people with the same name. Then does that mean you would have to make the name its own entity? Like if multiple people had the name john, then would they make it a foreign key attribute liking it to a seperate entity with the primary key called john
Lecture by Dr. Art Langer, author. Analysis & Design of Information Systems (3nd Ed), Langer, Springer-Verlag 2007 (ISBN978-1-844628-654-4)
October 22nd, 2009 at 7:10 pm
Correct! A table …
Correct! A table in the physical db is equivalent to an Entity in the LDM. A column within that table is equivalent to an Attribute in the LDM.
October 22nd, 2009 at 7:10 pm
A table in a …
A table in a database is Entity and column’s name in a table is Attribute. Am i getting it right ?
October 22nd, 2009 at 7:10 pm
An instance of …
An instance of recorded data — an actual record of information composed of one or more columns within a table — becomes a row within the physical database schema.
October 22nd, 2009 at 7:10 pm
When first learning …
When first learning about logical data modeling, it is common to confuse the definition of data structure with the instances of the data itself. Actually, the data elements that were referring to here are often called attributes. An attribute in the logical data model will become a column in the physical implementation of a table within a database schema.
October 22nd, 2009 at 7:10 pm
So, Elements are …
So, Elements are considered as rows or something else.
October 22nd, 2009 at 7:10 pm
That’s correct; the …
That’s correct; the data elements that repeat — those that potentially will have multiple instances — are segregated into a separate entity. The relationship among these entities is driven by propagation of the foreign key from the main entity to the subordinate entity (from the parent entity to the child entity).
October 22nd, 2009 at 7:10 pm
so I think you mean …
so I think you mean that you cant have attributes with more than one occurance. Like people cant have more than one name, but they can have more than one item that they are ordering. So then a seperate entity for items would need to be made with a relationship to the order?
October 22nd, 2009 at 7:10 pm
Don’t confuse the …
Don’t confuse the definition of attributes with the instance of values within the materialized table once you’ve actually created a table based on the logical data model. Remember that Entities are to tables as Attributes are to Columns.
October 22nd, 2009 at 7:10 pm
so that means that …
so that means that a different entity instance cant have any of the same non key attributes. So if there was the customer name attribute, there could be two people with the same name. Then does that mean you would have to make the name its own entity? Like if multiple people had the name john, then would they make it a foreign key attribute liking it to a seperate entity with the primary key called john
October 22nd, 2009 at 7:10 pm
Awesome, thanks for …
Awesome, thanks for uploading!