Hello jalil;
As described by DJM, SCADA is a control and data acquisition interface software, installed on computers (often PCs) and used with industrial automation controls (PLCs). They are generally developped by automation product manufacturers, (Rockwell, Siemens, Invensys, by some independants (often bought by larger automation industries, look at wonderware, Citect, Intouch), and sometimes by individuals who like their own interfaces in Visual C, Delphi... Communications are carried out over specialized buses such as Modbus, Profibus, Fieldbus, Industrial Ethernet... and the sensors, drives, motor controllers are designed to exchange with the PLCs over such links.
Building Management Systems are a parallel industry; components are diferent, manufacturers are more HVAC and lighting industrials (Carrier, Trane, Homneywell) and standards are different. They use different comm protocoles (BACNET, EIB, LonWorks) and different standards. Generally, industrial standards will use more power, control higher voltages, and use smaller gauge wire than building automation (LOL!).
I wrk as an automation engineer, mostly in industrial applications; but in the plants we design, we have to control or interface with BMS systems (HVAC, fire alarms, lighting controls); we often need to use protocol converters (BACNET to Modbus, for example) to interface between the systems). Here is one site I use to keep informed on the newer BMS developments:
http://www.modbs.co.uk/news/fullstory.php/aid/2483/Realising_the_intelligent_building_.html
Hope this helps,
Daniel Chartier