Hi all,

If I am asked to 'Design an ER schema for this application, and draw an
ER diagram for that schema'

is this not one and the same thing?

thanks

Portroe

ER diagram is only part of an ER schema. You also need a list of entities,
together with their attributes, identifier. Also any constraints and
assumptions.

Depending on the style of the course you're doing.

Mike
"portroe" <portroe (AT) nospam (DOT) com> wrote

Whoever asked you do this is wrong and has it backwards. An ER Diagram is an
Entity Relation Diagram and is used to help identify what _business_ data
needs to be captured, constraints on the data, and relationships among the
data elements. It is a logical model (as opposed to physical). There is no
such thing as an ER Schema . It is a Relational Schema, and it is created by
taking the ERD and applying certain transformation rules to it to create the
Relational Schema. A relational schema is a physical model listing the
actual tables, columns in the tables, Primary and Foreign keys, and certain
other constraints.

Often, The ERD step is omitted (by experienced designers) and a relational
schema is developed directly from an understanding of the business (they've
done this before). You can't really go backwards (relational schema to ERD),
and there is no real reason to.

"portroe" <portroe (AT) nospam (DOT) com> wrote