what is er diagram?

Question 10
You are asked to convert an existing two-tier client-server application interacting with Oracle database to java. What input is most needed to study feasibilty of that project in java? any one.
1) er diagram
2) application design
3) application code
4) list of gui objects

ER Diagram is an Entity-Relationship Diagram. Essentially it is a standard way to model Databases before UML. Truthfully most people still model databases using ER Diagrams instead of using UML.
I would also say that ER Diagram would be the best answer to question since a list of gui objects is useless, application code is irrelevant, and application design is what they plan to change in the first place (going from a 2-tier to an n-tier). I would want a list of use cases or at least a requirements list but neither of these are options, therefore I would be forced to go with the ER Diagram.

got it. thanks