Nowadays, structured data such as sales are stored in data warehouses for decision-making. Less-structured data such as HTML texts, XML data, images, and videos are increasingly accumulated in PC storage due to the spread of the Internet technology such as WWW. Such less-structured data, collectively called multimedia documents, are also precious as corporate assets. So we need to provide a document warehouse to analyze and manage multimedia documents for corporate-wide information mining and reuse like a data warehouse. As a document-intensive application of a multimedia database, we describe a prototype document warehouse system, which supports management of documents, keyword-based and content-based retrieval, rule-based classification, SOM-based clustering and XML active query facility based on ECA rules.