Based on this, I believe Section 5.9 should read:
`A PostgreSQL database cluster contains one or more named databases. Roles
are shared across the entire cluster, but no other data is shared across
databases. Any given client connection to the server can access only the
data in a single database, the one specified in the connection request.`
imo the following is a more precise wording:
'A cluster contains three or more named databases ('template0', 'template1', 'postgres', ...). Roles, which are users or groups, see Chapter 21, - as well as database names and tablespace definitions - are shared across the entire cluster. No other data is shared across databases or schemas. Any given client connection to the server can access only the data in a single database, the one specified in the connection request. If it has the necessary privileges, the connection can access all schemas within this database.'
And the last sentence of the paragraph behind 'Note' shall be extended, because schemas are rigidly separated from each other - only the access to different schemas is easily done from a single connection.
'Unlike access to databases, access to schemas is not rigidly separated: a connection can access objects in any of the schemas in the database they are connected to, if they have privileges to do so.'
J. Purtz