6.3 Data representation

There are many popular data storage formats, and many more than that in use. These formats are optimized (it they are optimized at all) for data storage, and are not generally suitable for data transmission. In order to transmit data over the Internet, OPeNDAP must translate the data model used by a particular storage format into the data model used for transmission.

If the data model for transmission is defined to be general enough to encompass the abstractions of several data models for storage, than this intermediate representation-the transmission format-can be used to translate between one data model and another.

The OPeNDAP data model consists of a fairly elementary set of base types, combined with an advanced set of constructs and operators that allows it to define data types of arbitrary complexity. This way, the OPeNDAP data access protocol can be used to transmit data from virtually any data storage format.

The elements of the OPeNDAP data access protocol are:

• Base Types These are the simple data types, like integers, floating point numbers, strings, and character data.
• Constructor Types These are the more complex data types that can be constructed from the simple base types. Examples are structures, sequences, arrays, and grids.
• Operators Access to data can be operationally defined with operators defined on the various data types.
• External Data Representation In order to transmit the data across the Internet, there needs to be a machine-independent definition of what the various data types look like. For example, the client and server need to agree on the most significant digit of a particular byte in the message

These elements are defined in greater detail in the sections that follow.

• 6.3.1 Base Types
• 6.3.2 Constructor Types
• 6.3.3 Operators
• 6.3.4 External Data Representation