The data archived in the system are stored in different formats depending on what type of data they are. A data type is generally characterized by the type of equipment that was used to collect it. We will use the CTD as an example. This instrument always comprises sensors for pressure, temperature, and conductivity. There may also be additional sensors to measure other variables such as dissolved oxygen, fluorescence, and light transmission. These data are organized in a spreadsheet where one column represents the value of a variable as a function of depth. This set of measurements is also described by a block of metadata that documents the data. The most important metadata are information on the sampling position, date, and time. Metadata are presented in a file in a standard way for a given data type. This is the how a data type is defined. A current meter may also take measurements of temperature and conductivity, but it must have measurements on current speed and direction. These data are also organized in a spreadsheet, but this time a column represents a variable's value as a function of time. These measurements are likewise characterized by a block of metadata, or header, that is different from that of a CTD.

The CTD data archived in the ODMS are in either the TS-8 or ODF-CTD format while current meter data are in TS-2 or ODF-MCM format. It should be noted that the TS formats will eventually be converted to ODF and the TS format will disappear.

Searching for data by the data type can be useful for users who are familiar with the data formats.