RE: Data Modeling Question
Date: Thu, 7 Feb 2008 14:07:37 -0600
Option 1 is not what you want. If you look in Tom Kyte's book "Effective Oracle by Design" on page 34, you will see why it is BAD.
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Ahbaid Gaffoor Sent: Wednesday, February 06, 2008 9:52 PM To: oracle-l
Subject: Data Modeling Question
We have a data model which looks like the following:
ITEM_CODE VARCHAR2(100) (Primary Key col 1) ITEM_TYPE VARCHAR2(100) ATTRIBUTE_001 VARCHAR2(4000) ATTRIBUTE_002 VARCHAR2(4000) ... ATTRIBUTE_250 VARCHAR2(4000)
ITEM_TYPE VARCHAR2(100) (Primary Key col 1) ATTRIBUTE_NAME VARCHAR2(1000) (Primary Key col 2) ATTRIBUTE_COLNUM NUMBER
It's a developer's dream of how we can store attributes for an item, the item type is used to decide which column holds what attributes by storing that metadata in the ITEM_TYPE_LU table. Initially, some 7 years ago the developer only dreamed of no more than 10 attributes per item. Today there are 205 attributes, some fields hold data that's a few characters and some the full 4000 characters.
I informed the development team that we face a max number of columns (1000 when I tested on 10.2.0.3)
Now we are undertaking a redesign to provide a data model that allows us to store an unlimited number of attributes.
The ideas we have in mind so far are:
- Switch to a row based schema, so the two tables become one, each attribute and its value taking a row for an item.
ITEM_CODE VARCHAR2(100) (Primary Key col 1) ATTRIBUTE_NAME VARCHAR2(250)
ATTRIBUTE_VALUE VARCHAR2(4000) So a single item would look as follows:
SELECT * from ITEMS where ITEM_CODE = 'shoe-001'; ITEM_CODE ATTRIBUTE_NAME ATTRIBUTE_VALUE
shoe-001 size 10 shoe-001 color brown shoe-001 price 15.45 shoe-001 manufacturer clarks
2) Use a CLOB column and store an XML document in it with all information:
ITEM_CODE VARCHAR2(100) (Primary Key col 1) ITEM_XML CLOB
SELECT * from ITEMS where ITEM_CODE = 'shoe-001';
shoe-001 <item> <item_code>shoe-001</item_code> <size>10</size> <color>brown</brown> <price>15.45</price> <manufacturer>clarks</manufacturer> </item>
3) Use Oracle's XML data types (not sure how this works)
I am partial to the first approach since I would be able to easily parse data when a business request needs it, also I can make use of Oracle partitioning to improve performance.
One other point to consider is that single attributes can be updated for an item, in the row based model this is simple, however in the CLOB based solution I am concerned that we need to replace the entire CLOB for a single attribute value change.
What I'd like is any advice pros / cons of the CLOB (approach 2) and the XML type (approach 3) solutions.
For scale, we are looking at close to 200 million items, each item having about 150 attributes each.
I am proceeding with approach 1 for now.
many thanks for your input
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