Difference between Logical Data Modelling & ERD
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Difference between Logical Data Modelling & ERD
What is difference between Logical data Modelling (LDM) & ER ?
Whenever we ask LDM , the customer gives ER diagram.
Whenever we ask LDM , the customer gives ER diagram.
sriramhariharan- Posts : 1
Join date : 2011-01-15
Re: Difference between Logical Data Modelling & ERD
The difference is between a logical model and a physical model. Both are presented as ER diagrams.
A logical model is slightly more abstract than a physical model. A physical model represents exactly what is implemented in a database... table and column names are as they exist in the schema, you define indexes, specify column datatypes and sizes, contraints, tablespaces, partitions and all the other requirements to actually define the database. A logical model shows entities, attributes, keys and relationships. Names are usually more free-form and descriptive.
A logical model is slightly more abstract than a physical model. A physical model represents exactly what is implemented in a database... table and column names are as they exist in the schema, you define indexes, specify column datatypes and sizes, contraints, tablespaces, partitions and all the other requirements to actually define the database. A logical model shows entities, attributes, keys and relationships. Names are usually more free-form and descriptive.
Re: Difference between Logical Data Modelling & ERD
When you ask for a LDM, what are you expecting?
BoxesAndLines- Posts : 1212
Join date : 2009-02-03
Location : USA
Re: Difference between Logical Data Modelling & ERD
Don't "conceptual models" sometimes get confused with "Logical Models".
A conceptual model might have a fact table with the dimension tables but without any column names. Some of the dimensions might later be split into 2 or combined. It's almost a graphic presentation of the BUS Architecture.
The logical model might have the column names in lay terms - "Group Identifier" instead of group_id. There may not be difference between a view and a table.
And the Physical Model is what the database physically looks like.
A conceptual model might have a fact table with the dimension tables but without any column names. Some of the dimensions might later be split into 2 or combined. It's almost a graphic presentation of the BUS Architecture.
The logical model might have the column names in lay terms - "Group Identifier" instead of group_id. There may not be difference between a view and a table.
And the Physical Model is what the database physically looks like.
Jeff Smith- Posts : 471
Join date : 2009-02-03
Re: Difference between Logical Data Modelling & ERD
Don't "conceptual models" sometimes get confused with "Logical Models".
Good point. Frankly, I'm confused most of the time. Maybe there needs to be a model model.
Re: Difference between Logical Data Modelling & ERD
To me, there is no logical dimensional model. Conceptual and logical models are normalized data structures used to define data dependencies. Unfortunately, there is no consensus on what goes into a conceptual model other than it is less than the logical data model.
BoxesAndLines- Posts : 1212
Join date : 2009-02-03
Location : USA
Re: Difference between Logical Data Modelling & ERD
How's this...
A Conceptual Model is what you on a scrap piece of paper.
A Logical Model is what you do in Excel.
And the Physical Model is what you get when you use Visio to reverse engineer the database.
Actually, a variation on the conceptual model comes in handy when setting up the reporting tools.
A Conceptual Model is what you on a scrap piece of paper.
A Logical Model is what you do in Excel.
And the Physical Model is what you get when you use Visio to reverse engineer the database.
Actually, a variation on the conceptual model comes in handy when setting up the reporting tools.
Jeff Smith- Posts : 471
Join date : 2009-02-03
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