The vast majority of work done on inventory system is based on the critical 
assumption of fully observed inventory inventory level dynamics and demand. 
Modern technology, like the internet, offers a tremendous number of opportunities 
to businesses to collect imperfect but useful information  which helps 
them planning efficiently to meet future demand. 
A good example is the internet. 
Visits to commercial web sites constitute a source of partial 
information on future demands of one or more of the 
commodities (or services) offered by companies. 
Many factors contribute to make inventories hard to be fully 
observed by the management. 
Using  Hidden Markov Models techniques we 
exploit partial information on inventory systems to 
estimate the current inventory level as well as future demands.
The parameters of the model 
are updated via the EM algorithm.