For more than a decade, OLAP and multidimensional analysis have generated methodologies, tools and resource management systems for the analysis of numeric data. With the growing availability of semi-structured data there is a need for incorporating text-rich document data in a data warehouse and providing adapted multidimensional analysis. This paper presents a new aggregation function for keywords allowing the aggregation of textual data in OLAP environments as traditional arithmetic functions would do on numeric data. The AVG_KW function uses an ontology to join keywords into a more common keyword.