Upper / lower cases on table and column names

(PostgreSQL) 7.1.1:

Hello all!

I was trying to adopt a database application to PostgreSQL.
(It is written for MySQL and Oracle using perl)

During this process I recognized the phenomena that upper case letters
of table names and column names are not preserved
in PostgreSQL.
Is this a "featue" of PostgreSQL or do I miss something?

Example:
Id and textId as a column name should conserve upper case letters 'I'
but \d data converts it to lower case words:

psql ...
create table data ( Id int not null, textId int not null);

\d data          Table "data" Attribute |  Type   | Modifier
-----------+---------+---------- id        | integer | not null textid    | integer | not null

and
create table Data ( Id int not null, textId int not null);

results in:
ERROR:  Relation 'data' already exists

In the interpretation of my application table 'data' and 'Data' is something 
different.

-- 
--
Mit freundlichen Gruessen / With best regards   Reiner Dassing