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The StruxureWare DCE server has a modbus output option, AP95MODBUS. With that, your BMS system can poll up to 247 slave addresses in DCE. You can poll data as well as alerts. Information for this integration can be found here:

http://www.apc.com/salestools/JRUK-7R4L9N/JRUK-7R4L9N_R3_EN.pdf 

The only other option to pull data from DCE would be to use the web API:

http://www.apc.com/shop/us/en/products/StruxureWare-Data-Center-Expert-Web-Services-API/P-SFWEBSVC