In this paper,we introduce the concept of web join for combining hyperlinked Web data.A web join is one of the web algebraic operator in our web warehousing system called Whoweda (WareHouse Of WEb DAta).It can be used to gather useful, composite information from two web tables.Web join and outer web join (a derivative of web join)operations can be used to detect and represen changes to hyper- linked Web data.We discuss the syntax,semantics and algorithms of web join and outer web join operators.We also presen how to detect and represen changes to hyperlinked Web data using these wo operations.