NETCDF Metadata Object Model

NETCDF METADATA OBJECT MODEL
Version 1 draft, last update: 2002/08/01

This document defines the Netcdf Metadata Object Model (NMOM) for generic data in netcdf format. NMOM includes only features which are common to all data in netcdf format, i.e. it was purposedly developed to be as simple and generic as possible. It is expected that NMOM for generic netcdf data will be extended by more specific object models for data in netcdf format following different conventions (COARDS, CF, etc). Note also that NMOM focuses on capturing the structure of the data more than the data itself, and leaves as optional the explicit inclusion of the physical data in the metadata.

Object	Properties (name: description)
Netcdf (object representing a netcdf dataset, for example, a netcdf file, or an aggregate of netcdf files, or a subset of a netcdf file)	dimensions: reference to 0 or more Dimension objects variables: reference to 0 or more Variable objects globalAttributes: reference to 0 or more Attribute objects id: unique identifier for the netcdf dataset (optional) uri: identifier (URL or URN) of the physical netcdf file (if it exists) from which the data is to be extracted
Dimension (object representing a netcdf dimension, i.e. a named index of specified length)	name: the dimension name length: the dimension length isUnlimited: flag indicating whether this dimension is flagged as unlimited in the netcdf dataset
Variable (object representing a netcdf variable, i.e. a multidimensional array of specified type indexed by 0 or more dimensions)	name: the variable name shape: reference to the Dimension objects that the variable depends on, ordered with more rapidly varying dimension last, same as C multidimensional arrays type: the data type of the variable values: a listing of the values of the variable attributes: reference to 0 or more Attribute objects
Attribute (object representing a netcdf attribute, i.e. a name-value pair of specified type)	name: the attribute name type: the data type of the attribute value: the attribute value if only one, or a listing of the attribute values if more than one separator: a token used to separate the listing of a multi-valued attribute

NOTES ON THE INTERPRETATION OF THE NETCDF METADATA OBJECT MODEL

The object model defines the properties of each object in generic terms, i.e. without prescribing a specific binding to a data type (string, float, array etc). The binding will need to be specified by a concrete implementation of the object model (for example, an XML schema, a C or Java application, etc.).
Any property of each object can be left undefined: for example, if a netcdf file does not possess global attributes, the globalAttributes property of the Netcdf object can be left undefined (null in Java, 0 pointer in C++, etc); or the values property of a Variable object does not need to be filled, unless the physical values are somehow important (as might be the case for a coordinate variable).