Sequence diagrams are very useful for APIs and understanding protocols between systems.
ER diagrams are great for presenting a database schema (just don't get too hung up the exact arrow you're using!) When I start a new major project, one of the first things I do is an ERD. You don't need every field (column, attribute...), but the tables (entities, objects, collections, whatever you want to call it...) and their relationships are pretty important.
ER diagrams are great for presenting a database schema (just don't get too hung up the exact arrow you're using!) When I start a new major project, one of the first things I do is an ERD. You don't need every field (column, attribute...), but the tables (entities, objects, collections, whatever you want to call it...) and their relationships are pretty important.