Dg201cj cmos quad spst analog switch

Hi..anyone here can explain to me what is the function of this device DG201 CMOS QUAD SPST ANALOG SWITCH? I had search using google or yahoo search machine but still cant find any site explaining this device. So if you know what is it please tell me or paste the link for me here. I dun want the datasheet. What i want is the theory behind it. Thanks..