In this paper, we present the DTDMatch system, which solves this problem by dynamically maintaining a set of sub-structures that are common to DTDs and documents. By using a sequence of filters that combine positive and negative information (which sub-structures in a newly arriving document can or cannot be instantiated by a DTD), the DTDMatch system quickly reduces the number of DTDs relevant to each incoming document, while guaranteeing no false negatives in the resulting set of candidates DTDs.XML is now widely accepted as a markup standard for data exchange. Given a large collection of closely related DTDs, and an XML document which doesn't specify which DTD it conforms to, a basic problem is to identify the DTD against which the document can be validated. This problem is challenging when the DTD identification needs to performed over a high-volume stream of XML documents.