Separation of the physical and logical structures

Question

Hi,
I am very new to Oracle database administration. While reading Sam Alapati's book "Expert Oracle9i Database Administration," I came across the concept of the separation of an Oracle database’s physical storage structures from its logical storage structures. In particular, Sam states the following in his book:
“This logical defining of Oracle's database structure has another fundamental motive behind it. By organizing space into logical structures and assigning these logical entities to users of the database, Oracle databases achieve the logical separation of users (owners of the database objects, such as tables) of the database from the physical manifestations of the database in terms of data files and so forth.”
I am not quite convinced about the value this separation of the physical and logical really adds to the task of database administration. Considering the way DBASE worked, i.e. each table used to be stored as a separate file, what would be lost if Oracle’s implementation were similar and each table (i.e. file) were to be assigned to a particular user. I am not sure of the value added by storing the data from more than one table in more than one file, effectively resulting in a many-to-many relationship between tables and files. Please enlighten me. I would really appreciate it.
Karim

Answer 1

and each table were to be assigned to a particular user. Don't know what you mean. In Oracle, every table has one and only one owner.
I am not sure of the value added by storing the data from more than one table in more than one fileIf an application has a thousand tables, would you rather manage 1000 files or 1?
In general, separating the physical from the logical allows the physical structure to change without affecting the logical (in theory at least). Even a table is a logical structure. We think of rows and columns, but it isn't stored the way we think of it. When we do a select statement, we don't have to write code to read each block, extract the contents, etc.
With partitioned tables, it is sometimes a good idea to split up partitions in such a way to get a performance gain. Like placing the most recent (and most queried) month of data on the fastest storage device. If you stuffed everything in to one gigantic file, you would lose that ability.
If you want to store each table as a separate file, you can do that with Oracle. For each new table, create a new tablespace, and then create a new file for the tablespace. Then come back to this forum in a year and tell us how it's going.