PL/SQL is a block-structured language. Like Pascal it treats a procedure, function or a program as a logical block that might contain any number of nested sub-blocks. A logical block is made up of declarations and statements, and the declarations are local to the block.
As shown above, a PL/SQL block is made of three parts: a declarative part, an executable part, and an exception handling part. Any error or a warning condition is called an exception in PL/SQL. Only the executable part is necessary.