I may not be remembering this correctly, but is it correct that schemas also differ between Oracle and SQL Server as the schema is unique to the instance in Oracle whereas in SQL Server it is unique to the user database e.g. the DBO schema?
Very true. The autor is saying the same thing in the article
The objects that a user owns are collectively called schema. A schema is bound to exactly one user (in Oracle). A SQL Server database has the features of an Oracle scheme because objects are created inside the database
In other words, there is 1:1 relationship between a user and a schema in Oracle, unlike in SQL Server. Therefore, a scehema in Oracle can be equated to a database in SQL Server.
Actually both statements are false.
In Oracle the user is not defined as unique in the instance, but unique in the database, as in SQL Server. Oracle's limitation of one database per instance is another issue.
Objects in SQL are created in a schema, not in a database. It looks like they are created in a schema because there's always a default schema for each database user.
The bigger difference is that SQL Server, starting with 2005, finally fixed the issue of confusing user with schema.