A metadata registry is a central location in an organization where metadata definitions are stored and maintained in a controlled method. A metadata repository is the database where metadata is stored. The registry also adds relationships with related metadata types. A metadata engine collects, stores and analyzes information about data and metadata (data about data) in use within a domain. Use of metadata registries Metadata registries are used whenever data must be used consistently within an organization or group of organizations. Examples of these situations include: Organizations that transmit data using structures such as XML, Web Services or EDI Organizations that need consistent definitions of data across time, between databases, between organizations or between processes, for example when an organization builds a data warehouse Organizations that are attempting to break down "silos" of information captured within applications or proprietary file formats Central to the charter of any metadata management programme is the process of creating trusting relationships with stakeholders and that definitions and structures have been reviewed and approved by appropriate parties. Common characteristics of a metadata registry A metadata registry typically has the following characteristics: Protected environment where only authorized individuals may make changes Stores data elements that include both semantics and representations Semantic areas of a metadata registry contain the meaning of a data element with precise definitions Representational areas of a metadata registry define how the data is represented in a specific format, such as in a database or a structured file format (e.g., XML) Clear separation of semantics and system-specific constraints Because metadata registries are used to store both semantics (the meaning of a data element) and systems-specific constraints (for example the maximum length of a string) it is important to identify what systems impose these constraints and to document them. For example the maximum length of a string should not change the meaning of a data element. The International Organization for Standardization (ISO) has published standards for a metadata registry called ISO/IEC 11179 and also ISO15000-3 and ISO15000-4 ebXML registry and repository (regrep) EbXML RegRep International standards There are two international standards which are commonly referred to as metadata registry standards: ISO/IEC 11179 and ISO 15000-3. There are some who believe that ISO/IEC 11179 and ISO 15000-3 are interchangeable or at least in some way similar. e.g. "Of interest is that the ISO 11179 model was one of the inputs to the ebXML RIM (registry