>However, in my POS/Invoice module, program will not know the item type key-in/scanned at least search from database. Since, I have multiple of Item class (each for each type of item), how to know which class should be initiated for SKU/Barcode lookup? Should I create one more class just for lookup, then create a appropriate object??

I'd create a "lookup" class, and then have that class instantiate the appropriate "item" class.

I have something similar in my Inventory module which has many different types of "documents"; eg. Purchase Order, Order Receipt, Stock Issue, Return to Stock, Return to Vendor, Inventory Count, Inventory Adjustment, etc.

There is a Document "front-end" that allows a User to retrieve one or more Documents (current or archived) and perform some action (Validate, Validate and Post, Post, Print). This front-end instantiates the appropriate "document object" (which is a subclass of a "document processor" class) based on document type, sets some properties, and then lets the document object execute.