1.1.2 An Example: Using OPeNDAP

To produce the same data selection using OPeNDAP, a user would follow essentially the same steps. However, the steps themselves would be performed differently. Once the user's data analysis package has been converted to an OPeNDAP client (Section 3.1), the accesses to the remote datasets are made through the analysis package itself. Instead of specifying a data file by a pathname reference to some local disk file, the user specifies a URL, which may point to either a local or a remote dataset. Here is a re cap of the same operation, outlined as they would be performed by an OPeNDAP application program:

1. Create the time series from the COADS Climatology archive. This is done by using the sampling facilities of whatever data analysis program a scientist is familiar with. If desired, OPeNDAP constraint expressions may be used to reduce the network load, or to provide a sampling scheme not supported by the data analysis program.
2. The data need not be imported to the user's data analysis program, since it was down-loaded and converted automatically in step 1.
3. Examine the data and formulate a request to the AVHRR archive. This is again done through the sampling facilities of whatever data analysis program the user is using, and OPeNDAP constraint expressions. Note that, whatever their actual format, both COADS and AVHRR archives appear to the OPeNDAP client to be stored in identical formats.
4. The data need not be imported to the user's data analysis program, since it was down-loaded and converted automatically in step 3.
5. Think about the results.

It is important to note that any data analysis package that can handle one of the DODS-supported data access APIs can be converted into an OPeNDAP client program capable of reading data stored by all of the DODS-supported data access APIs. (There are some limitations on translation. See Section 1.1.3 and Section 6.1.2 for more information.) Therefore, assuming the user has some analysis package capable of doing the required sampling and analysis on local data, all the steps would be performed from within that package, just as if the user were operating on local files. The result is a simpler procedure, even though the same essential steps are followed.

The OPeNDAP scenario has, among others, the following advantages:

• The user need not learn about any of the archival formats, since the OPeNDAP server and client cooperate to deliver the data in the format in which the analysis package expects to see it. Whereas the user of the ftp server has to worry about importing the data into the analysis program, the OPeNDAP client program imports it transparently.
• The user can sample the distant datasets in any fashion supported by his or her own (local) analysis package. Unnecessary data need not be sent over the Internet.
• By appending a constraint expression  to the URLs given to the analysis program, the user can sample data using techniques that their analysis program cannot do.²
• A substantial amount of the searching and sampling is performed on the server machines. This reduces Internet traffic, as well as decreasing the load on the local machine.