Distributed Data Access Information
Table of Contents
- Functional Overview
- Getting Started
- Desktop Services (Clients)
- OPeNDAP Servers
 Functional
Overview
The NOMADS framework is a distributed data system
that promotes the combining of data sets between
distant participants using open and common server
software and methodologies. Users effectively
access model and observational data and products in a
flexible and efficient manner from archives or in
real-time through existing Internet infrastructure.
The framework of the server and software used to
manipulate the archive data base and distribute the
real time data is the Open source Project for a Network
Data Access Protocol (OPeNDAP) formally known as the
Distributed Ocean Data System (DODS). OPeNDAP is a
binary-level protocol designed for the transport of
scientific data subsets over the Internet.
Through OPeNDAP applications can open and read subsets
from remote data sets.
The
Grid Analysis and Display System (GrADS) is an open
source desktop tool that integrates the analysis and
display of a wide variety geophysical data. OPeNDAP is an
open source software project that provides a way to
share data over the Internet. NOMADS combines these
technologies to greatly expand the utility of the
client and server concept. DODS/OPeNDAP-enabled clients
such as GrADS, Ferret, IDL, Matlab, and end-user
programs linke with various DODS/OPeNDAP
client-libraries, can can access datasets and subsets
of datasets over the network from DODS/OPeNDAP servers.
The server can perform calculations over large amounts
of data and only transmit (fairly small) results back
to the client. This avoids transmitting large amounts
of data to the client.
"Downloading data from the DODS/OPeNDAP server to
your local system is generally a misuse of the
DODS/OPeNDAP server. The DODS/OPeNDAP data server is
like a library in the purist sense of the term. When
you check out a book from the library, do you
photocopy the entire book, return it, and then read
your copy? It is difficult to overcome the habit of
working with data that you don't actually have on
your own disk. The capability to access and use
gigabytes of binary data over the Internet has not
existed before. It does not make sense for terabytes
of disk across many institutes to be redundantly
occupied by the same data that are freely available
over the net."
Getting
Started
Desktop
Services (Clients)
For data users, the currently available OPeNDAP
servers include data formats for many desktop
applications, and the user base for OPeNDAP enabled
clients is expanding. NOMADS users have multiple
options to access data from their desktops. The OPeNDAP web
site maintains a
list of OPeNDAP-enabled analysis applications and libraries.
With a certain level of understanding of the OPeNDAP protocol, a user can also
use a web browser or even a
spreadsheet to access OPeNDAP data.
OPeNDAP
Servers
A data provider can range from a single scientist
and a laptop computer, to a major data center. To make
data available under the NOMADS framework, a provider
must install an OPeNDAP Server as described on the
OPeNDAP web site.
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