BibSonomy publications for /user/schmitz/algebraThu Mar 22 17:02:44 CET 2007CIKMconf/cikm/9681-88A Data Model for Supporting On-Line Analytical Processing.1996olap algebra model database relational folksonomy Thu Mar 22 17:02:06 CET 2007ACM Trans. Database Syst.4566-592Extending Relational Algebra and Relational Calculus with Set-Valued Attributes and Aggregate Functions.121987database algebra folksonomy relational