Logical data model

Figure 4-3: Data Modelling Today (Photo credit: Wikipedia)

Logical data models help to define the detailed structure of the data elements in a system and the relationships between data elements.  In Enterprise Architect, a Logical data model is typically represented using the UML Class notation.

no guessing but predict where data will go..

Example
form order #, order date, customer #, customer name,customer address,
we will look this information under header.

then comes details
Item #,item details, item quantity, item price, and item total and then we will have line items or every item associated with this order.

At bottom, items total amout.(totalling of all items)
to convert into database..
logical data modelling
3 most crucial
1) identify candidate keys
2) Selective primary key
3) Apply normilization

eventually give entity relation diagram (ERD)

What is candidate key.. what do you mean by key

each field is called data elemant.
and we have to find unique key.
Most popular is Social security as no two employes can have same #.
Order # will be a candidate key