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Q: What is the Java Metadata Interface (JMI) Specification? A: JMI is a standards-based, platform independent, vendor-neutral specification for modeling, creating, storing, accessing, querying, and interchanging metadata using UML, XML, and Java. Q: What problem does JMI solve?A: The complexity of the various artifacts of computing (components, APIs, interfaces, enterprise and other services, whether local or distributed)continues to increase. As more and more disparate information and other resources are being made available on the web, the burden to integrate these resources is becoming large. One of the reasons that these resources are difficult to integrate is that they all have their own (unique, and often proprietary) view of their data and its meaning. By providing a platform-independent standard for modeling, representing, and querying the meaning of a data source's data (its metadata), application, tool, and data integration can be substantially improved. JMI provides such a platform. Q: What is metadata?A: Metadata is simply data about data. It defines the structure and meaning of data objects. Examples of metadata include database schema, the meaning of object attributes and methods in a Java class, XML DTDs and Schemas, and UML models. Q: Why is metadata important?A: Data cannot be interpreted without metadata (also called semantics). For example, if we encounter the integer value "39" in a program, we cannot understand what it means without additional information. Much of this information tends to be embedded in the systems that use them, making the sharing of data and components extremely difficult. Q: What are some examples of metadata requirements in different domains?A: Metadata is required in virtually all application domains. For instance, in the areas of:
A: With metadata management, we can:
A: JMI provides a metadata framework that can capture the semantics of the data systems use. Using industry standards, it provides a common semantic model for describing metadata, a common Java-based programming model for managing metadata, and a common interchange format for exchanging metadata. Q: Is JMI platform independent?A: Yes. JMI is a mapping of the MOF (Meta-Object Facility) model from the OMG (Object Management Group) to the Java Programming Language. Both of these technologies are platform independent. Q: What are the main features of JMI?A: JMI defines:
A: The models of metadata used by JMI are created using MOF, which uses a subset of the UML notation to describe a few basic abstractions. These basic artifacts can then be used to build models (metamodels) of any kind of metadata. Many UML tools allow for the export of these models via XMI (the XML Metadata Interchange standard). Q: How does JMI work?A: Given a MOF-compliant metadata model, a Java API that precisely reflects the model's structure is automatically generated by JMI. Applications can use either this API, or JMI's generic reflective API ,to interact with metadata instances, performing discovery, traversal, query, and lifecycle operations. Thus a mechanism can be built to facilitate interoperability with generic metadata. Q: Which version of the MOF model does JMI define the mappings for?A: MOF 1.4.
Q: Which version of Java 2 Standard Edition (J2SE) is JMI compatible with? A: JMI is compatible with J2SE version 1.3 or above. Q: What is the relationship between JMI and J2EE?A: JMI is compatible with J2SE version 1.3 or above. Q: How does JMI fit into Sun ONE?A: JMI is an extension technology that brings the power of model-based metadata managment and application development to Sun ONE, Sun's integratable architecture for constructing scalable, reliable, and secure distributed enterprise applications. Q: We already have XML. Why don't we use XML instead of JMI?A: First of all, XML is a data type system, not an object model. The simple, containment-based data model in XML cannot be used to express general metadata semantics like classes, associations, attributes, and methods, to name a few. Moreover, the various XML "DTD standards" so common in the industry today define only the interchange format for data, not a standard semantic for the objects themselves. XML alone does not tell users the meaning behind the semantics, does not provide a true object model, does not provide multiple levels of abstraction, and is not visual. JMI (and MOF and XMI) provide all of these. Q: My Company has adopted UML and MOF already. Is JMI interoperable with these technologies?A: Yes, through the use of XMI, the XML Metadata Interchange standard. Q: Is the JMI specification finalized yet?A: Yes. The final release of the specification was made on June 28, 2002, and is available from the JCP website at http://jcp.org/jsr/detail/40.jsp. The reference implementation and TCK are also complete and can be accessed from the same location. Q: How will JMI be delivered?A: Two open-source implementations of JMI are already available (see the downloads page on the JMI website referenced below). Additionally, numerous vendors are building support for JMI into their products. Links to these products can be found at the JMI website. Q: Where can I find additional resources about JMI?A: Check out the JMI website at http://java.sun.com/products/jmi/.
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Oracle is reviewing the Sun product roadmap and will provide guidance to customers in accordance with Oracle's standard product communication policies. Any resulting features and timing of release of such features as determined by Oracle's review of roadmaps, are at the sole discretion of Oracle. All product roadmap information, whether communicated by Sun Microsystems or by Oracle, does not represent a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. It is intended for information purposes only, and may not be incorporated into any contract.
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