9. Metadata and XML
The key to developing an Internet based marine data framework is metadata. Metadata is becoming a widely understood process and is being used in a large number of applications. The best known form of metadata is its use as a data inventory or directory to help users locate data. Within IODE, the Marine Environmental Data Inventory (MEDI) Pilot Project is being developed to provide this type of metadata directory system. Another form of metadata is the detailed descriptions that are kept with a data set to help future users understand that data.
In an Internet context, metadata is used as a mechanism to display information (HTML) and also to describe the content of the data set (XML). Most people have some understanding of HyperText Markup Language (HTML) which is used in web environments to display or render information. The eXtensible Markup Language (XML) differs from HTML in that it describes content. With the emergence of XML as a data transfer protocol there is now available a mechanism to support the exchange of marine data. XML changes the way data moves across networks, it encapsulates data inside custom tags that carry semantic information about the data.
XML has been developed and is managed by the World Wide Web Consortium. It is a standard that enables the creation of tags that define content. In addition to this, the web browser or other software such as a database or visualisation packages can be made to understand the nature of the data automatically. By applying a different stylesheet to the same data set, an XML tagged dataset can be displayed in different formats. The key is that with XML the information is in the data, while the rendering instructions are elsewhere, separating content and presentation.
XML applications provide many advantages particularly in relation to the exchange of data. Because different organizations (or even different parts of the same organization) rarely standardise on a single set of tools, it takes a significant amount of work for two groups to easily exchange data. XML will allow data managers to send structured data across the web so that nothing gets lost in translation. Many groups are developing industry specific XML tags, to automate the transfer of data between disparate systems. These include the financial industry with their own version of XML and chemistry researchers have also developed an extension to XML to facilitate the exchange of chemical data. The United States of America Navy has developed a version to support the transfer of meteorological data.
XML provides a structured and machine readable framework for the creation of metadata descriptions of marine data that will significantly improve the ability to integrate, manage and transfer data from one system to another within minimal human involvement. The development of a marine metadata system based on XML will provide the ability to encapsulate all necessary information with the data itself. The information can include the traditional metadata including who collected the data, how it was collected and where it now resides. However, other information can also be added including electronic water marking to ensure ownership issues are addressed.
The simple process of reducing or avoiding the need to translate data from one format to another would save many hundreds, if not thousands of hours in the data centres and agencies processing marine data. The potential cost savings from this are very large. However this is not the only benefit. XML may provide the ‘missing framework’ that is needed to create the Virtual Data Centre discussed earlier.
