A key part of any marine dataset is the accompanying metadata. Metadata are "information about data" and can include characteristics about the data such as the content, accuracy, reliability and the source. Metadata provide the mechanism to describe data in a consistent form which allows users to gain a uniform understanding of the content and fitness for purpose of datasets.

Metadata have many applications. It can be used to:

• concisely describe datasets and other resources using elements such as the name of the dataset, the quality, who is the custodian, how to access the data, what is its intended purpose, who to contact for more information about the data

• enable effective management of resources

• enable accurate searching and resource discovery

• provide an online interface to a dataset and link to other information about it

• accompany a dataset when it is transferred to another computer so that the dataset can be fully understood, and put to proper use, and to duly acknowledge the custodian on the dataset.

Metadata help people who use marine data to find the data they need and determine how best to use it. Metadata benefit the data producing organisation as well. As personnel change in an organisation, undocumented data may lose their value. New employees may have little understanding of the contents and uses of a digital database and may find they don't understand the results generated from these data. Lack of knowledge about other organisations data can lead to duplication of effort. It may seem burdensome to add the cost of generating metadata to the cost of data collection, but in the long run it is worth it.

The information needed to create metadata is often readily available when the data are collected. A small amount of time invested at the beginning of a project may save money in the future. Data producers and users cannot afford to be without documented data. The initial expense of documenting data clearly outweighs the potential costs of duplicated or redundant data generation. The MEDI system provide a tool for metadata management and data discovery for national, regional and global marine datasets.