See the link :
Hope this helps,
POSDM is an Add-on component of BI 7.0.
There will be 2 types of Scenarios in IS Retail,BI & POS integration.
1) ECC Outbound : Master data will flow from IS retail to POS ...like Assortment list, Bonus Buys,Promotions,merchendise Hirarchy.
2) All the Sales & Payment data coming from POS will be uploaded in POSDM ...In POSDM there will be Different tasks for sending data to IS Retail & BI.
POSDM will show aggregated sales , Payments data ..also Promotion and Bonus Buys...
If you are using SAP POS...then Standard XI Contents are available for the Integration.
But For 3rd party POS ..you need to develop all the XI interfaces for Integration.
Implementing for 150 Stores or 1000 is all depends on following Scope points.
1) How many Different POS Systems in the Organisation?
2) How many formats of Retail Business they have?
3) How many Interfaces to Develop apart from from Standard SAP Retail Interface?
4) What kind of Landscape they Use, whether they go for SAP XI or Third party Integration tool.
5) What kind of Checks or Enhanced cheks to be Implemented?
This is also basically scope questions which need to be cleared, then you can decide on the Number of days required to Implement.