This paper presents AROM, a new object-based knowledge representation system. AROM is original in two ways. Firstly, in addition to classes, knowledge representation in AROM uses associations for describing links between classes instances. Secondly, AROM integrates an algebraic modeling language (AML) for describing operational knowledge (equations, constraints and queries) in a declarative way. AROM comes as a platform for knowledge representation and manipulation. It includes an interactive modeling environment, a Java API, an AML interpreter for processing queries and solving sets of equations, and a tool for consulting and editing knowledge bases on the Web.