Syntax of the DODS URL

Table: DODS URL Syntax

DODS URL	Access :// Host / CGI / Args
Access	http
Host	Domain name
CGI	CGI-directory / String
Args	Pathname
	Pathname Constraint
	( DODS URL )
Constraint	? Expression

Access

The access component of a DODS URL is always the literal string http. The DODS data delivery architecture described in DODS--Data Delivery Architecture uses the World Wide Web HTTPD server developed by NCSA to transport data. Note that just about any WWW server will work for DODS as long as it supports the CGI mechanism.

Host

The host component is an Internet-style host name that can be resolved to an Internet address.

CGI

The CGI directory is the directory where CGI programs are kept. This varies from machine to machine but many UNIX computer use cgi-bin. In addition, it is possible to configure httpd to search several directories for CGI programs; the DODS dispatch CGI may reside in any of these directories. The string is the name of the DODS dispatch CGI. In the software distributed by URI/MIT this is an abbreviation for the API (e.g., the dispatch CGI for NetCDF is nc). However, server implementors are free to choose any name they want. In addition, data providers may rename this script if they want to.

Args

The URL components named Args contains a pathname used by the CGI to locate the data set. This may or may not be an actual path on the remote machine. In some cases the DODS server may be an interface to a DBMS. In this case the pathname is used (probably in conjunction with other information) by the CGI to formulate a query to the DBMS. The pathname may have a constraint expression appended to it. This is used either by the filter program or the CGI to limit the data access beyond the pathname. It provides additional flexibility in the way data is accessed through the server. The arguments may also be a second URL. In this case the Access and Host components of the outermost URL (called an envelope) specify the target process (server) which should receive the embedded DODS URL. The source process (client) does not interpret this embedded URL at all--only the target process attempts to evaluate it. Embedded URLs may be nested to any depth.

Constraint

The constraint is a boolean expression used to constrain access to a variable. Different classes of variables can have different types of constraints. See DODS--Data Access Protocol for a more complete discussion of constraints.

Table: Sample URLs which name resources; sometimes there is more than one acceptable way to name a single resource.

URL	REFERENCES
http://gso.uri.edu/cgi-bin/nc/data/fnoc1.nc	the entire data set
http://gso.uri.edu/cgi-bin/nc/data/fnoc1.nc?u	u from the data set
http://gso.uri.edu/cgi-bin/nc/data/fnoc1.nc/u	u using the virtual file system syntax
http://gso.uri.edu/cgi-bin/nc/data/fnoc1.nc?u<10	all variables given that u is $<$ 10 (Makes sense for sequence data only)
http://lake.mit.edu/cgi-bin/jg/bloom/level1	all variables in level1
http://lake.mit.edu/cgi-bin/jg/bloom/level1/temp	only temp in level1