Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database
The SYSTEM tablespace is created automatically for each new Oracle database. It contains all the data dictionary objects for the entire database.
Yes we can enforce integrity constraint on a table if some existing table does not satisfy the constraint by using "ENABLE NOVALIDATE"
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and can?t be changed latter
A data block size is defined by DB_BLOCK parameter in pfile and there could be non standard block sizes supported by Oracle upto block size of 32bytes
Once set the block size could not be changed and the database has to be created again
An integrity constraint is a declarative way to define a business rule for a column of a table.
Yes a Tablespace can hold objects from different Schemes in Oracle