# What is DDL (Data Definition Language)?

As a part of my curriculum, I am studying principles of DBMS from the book by Silberschatz and Korth.
A part of it is about Data Definition Language (DDL).

I understand, in normal terms, that DDL is any set of commands that modify the schema and not the actual data. That is the simple way of putting it. A certain paragraph in the book states, in addition to what I said, as below:

We specify the storage structure and access methods used by the database system
by a set of statements in a special type of DDL called a data storage and definition language.
These statements define the implementation details of the database schemas,
which are usually hidden from the users.


Can someone please explain to me what the first two lines mean ?
AFAIK, storage structure here would refer to the tables, in RDBMS, and access methods would refer to the views because they define what the user gets to see ?

Still, a simple explanation on this is welcome :)

• The questions doesn't seem to be a research-level question in theoretical computer science, please consider posting such question on Computer Science which has a broader scope. – Kaveh Aug 28 '13 at 4:51

Operations on a database are divided into DDL and DML.

DDL are operations that alter the structure of the database. This includes creating/dropping tables, constraints, indexes, packages, views, dblinks, adding or removing columns to a table, changing object names and so on.

DML are the operations that alter the data stored in the database. This includes inserting, deleting and updating rows to/from a table.

• What does the author mean by storage structure and access ? :) – Little Child Aug 26 '13 at 18:37
• Specifying the storage structure means defining the layout of the tables that will be used to store the data (how many tables, what columns on each table, etc). Defining the access methods means granting insert/delete/update privileges on those tables, as well as creating packages such as Table API's that will be used control those insert/delete/update operations. – Arzaquel Aug 26 '13 at 19:32