The OPeNDAP provides a way for ocean researchers to access oceanographic data anywhere on the Internet from a wide variety of new and existing programs. By developing network versions of commonly used data access Application Program Interface (API) libraries, such as NetCDF , HDF , JGOFS , and others, the OPeNDAP project can capitalize on years of development of data analysis and display packages that use those APIs, allowing users to continue to use programs with which they are already familiar.
The OPeNDAP architecture uses a client/server model, with a client that sends requests for data out onto the network to some server , that answers with the requested data. This is exactly the model used by the World Wide Web where client programs called browsers submit requests to web servers for the data that make up web pages. Of course, OPeNDAP clients can do much more than browse this data. Using flexible data types suitable for many uses, including scientific data, the OPeNDAP servers deliver real data directly to the client program in the format needed by that client.
In fact, the network communication model used by OPeNDAP uses URL addresses and web servers (httpd) to deliver data to the researcher. This is done by using the OPeNDAP software to convert a researcher's data analysis software into a sophisticated (though specialized) web browser. In addition to providing network-compatible versions of popular data access APIs, the OPeNDAP project also provides a software client and server toolkit to help other developers create network-compatible OPeNDAP versions of other APIs.
To expand the universe of data available to a user, OPeNDAP incorporates a powerful data translation facility, so that data may be stored in data structures and formats defined by the data provider, but may be accessed by the user in a manner identical to the access of local data files on the user's own system. Though there are limitations on the types of data that may be translated (See Section 6.1.2), the facility is flexible and general enough to handle many of the possible translation. There are two important results:
The combination of the OPeNDAP network communication model and the data translation facility make OPeNDAP a powerful tool for the retrieval, sampling, and display of large distributed datasets. Though OPeNDAP was developed by oceanographers, its application is not constrained to oceanographic data. The organizing principles and algorithms may be applied to many other fields where data can be stored on computers.
The population of people who may be interested in a system such as OPeNDAP may be divided into data consumers and data providers. Though it was an important observation to the development of OPeNDAP that the two roles are often assumed by the same scientists, the division is a useful one for the introduction of the system. The following two sections provide a broad introduction to the roles of data consumer and data provider. The remainder of this guide is organized around this distinction between classes of users.