10.9 XML Metadata Interchange
10.9 XML Metadata Interchange A recurring theme throughout this chapter is that CWMI is used to exchange metadata between systems. The question is how it does this. What are the mechanics of the exchange? How do we actually transfer the metadata information from one system to the next ? In Chapter 9, we discussed XML and how it is used to exchange structured documents between systems. Since CWMI has a structure, it is only natural to apply XML and use that structure as the medium of metadata exchange. This is the XML Metadata Interchange (XMI). XMI is the method by which data warehouse metadata that conforms to the CWMI metamodel is communicated. XML is particularly attractive for exchanging metadata. XMI format becomes independent of any specific middleware technology. It enables CWMI to become truly open. Any tool or application can read and generate an XML document. This of course makes it possible for them to read and generate XMI documents, which in turn makes it possible for any tool to communicate with any other tool via XMI. We can view CWMI metadata as just another source of data for XML. This is a huge benefit for XMI. Standard tools for the composition and validation of XML documents are available for XMI. Using the XML Document DTD Production Rules, the tools can communicate the metamodel between systems. As we discussed in Chapter 9, the DTD describes the structure of the document. The XMI DTD describes the structure of the metadata. XMI then generates an XMI document containing the metadata using XML Document Production Rules . Just as CWMI can serve as another source for XML, it also acts as a destination. The target system receives both the XMI DTD and the XMI document. Again, we can employ the use of standard XML tools. These tools, using the DTD, decode the XMI document and reconstruct the metadata.  |
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EAN: 2147483647
Pages: 113