An announcement from the Financial Information Services Division of the Software and Information Industry Association (SIIA) describes the publication of the Market Data Definition Language (MDDL) Version 1.0. MDDL is "a publicly available standard that provides a generic XML-based message format and glossary of fields needed to describe financial instruments, corporate events, and market related indicators. The function of MDDL is to promote data interoperability as well as to provide a standard taxonomy for market data. MDDL Version 1.0 covers equities, mutual funds, and indices; future versions will be expanded to include all financial information necessary to account, analyze, and trade within a market. The initial use of MDDL is for end-of-day and snapshot applications but it has been designed to be extensible to streaming, historical, and other applications as appropriate." Acccording to Mark Hunt (Director of XML Strategy at Reuters, and Member of the MDDL Steering Committee), the MDDL V1.0 standard is "an important milestone in the financial services industry's use of XML, and will allow vendors and users alike to make more of their data."

MDDL Taxonomy: the MDDL project maintains an online "Glossary of Controlled Vocabularies." The Registry of Controlled Vocabularies is a list of Controlled Vocabularies compatible with MDDL. For each entry in the table, clicking on the name of the controlled vocabulary will display a readable version of the controlled vocabulary..."