Open Data Access Protocol Webb Pinner May 2, 2005 CSC 536

Acknowledgements Peter Cornillan - Graduate School of Oceanography, DODS James Gallager - OpenDAP.org Tom Sgouros - OpenDAP.org John Howland - Deep Submergence Lab, Woods Hole Oceanographic Institute

Outline of Presentation Background Information The OpenDAP protocol Oceanographic Dive Reply System Summary Questions?

Background DODS was created in 1993 by URI, GSO, MIT, NASA and NOAA for use in oceanographic datasets. It's purpose was to "define the structure of a client-server based distribution system for access to oceanographic data over the Internet”

Background (cont.) DODS was quickly adapted for use by the atmospheric data community. Because DODS no longer dealt with strictly with ocean data the name was changed to the Data Access Protocol 2002 the project was made open source and thus OpenDAP was created

The OpenDAP Architecture Provides uniform interface to data Allows SQL-like data querying Read-only access to data Platform independent Client/server model For use over Internet (TCP/IP)

OpenDAP Implementation Uses http as transport protocol –Server implemented as CGI extension in Apache webserver –Requests for data are sent to server in the form of a URL URL sent to server describes exactly what data is requested –Includes which columns and/or data constraints.

Example URL –http - protocol –dap_server - servername –cgi-bin/nph-dods - dap server software location –data - director where dataset is located –dataset1 - name of dataset Extension determines which service is called Constraints may be added to request specific datasets

OpenDAP Implementation (Services) Three basic services: –Data Descriptor Service (DDS) –Data Attribute Service (DAS) –Data (DODS) Additional services: –HTML form (HTML) –ASCII representation (ASCII)

OpenDAP Implementation (Constraints) Constraints specify which fields to display and in what order to display them. – Constraints specify search criteria. –

Current Users NASA - Global Hydrology Resource Center NOAA - National Data Buoy Center (NDBC) NOAA - National Oceanographic Data Center (NODC) University of Hawaii/SOEST - Sea Level Center (SLC) Woods Hole - Upper Ocean Mooring Data Archive (UOP)

OpenDAP DEMO

OpenDAP = Middleware/Dist. System? Kinda, sorta, not quite Uniform interface to data (Middleware) User is unaware of OS, storage format or access protocol (Middleware) Data distributed across multiple servers (Dist. System)

OpenDAP = Middleware/Dist. System? Read-only Access Each Dataset is independent of other datasets No such thing as replication, commit protocols, concurrency control, etc.

Oceanographic Dive Replay System

Replay a dive complete with textual data and images Retrieve data from remote servers Provide a graphical means to interact with large ascii datasets Provide means to search dataset

WHOI - Virtual Vans

Replays a dive complete with textual data and images Retrieves data from WHOI server Provide a HTML based GUI Provide means to search event data

Virtual Vans - Shortcomings Unable to search by any other dataset Unable to create custom datasets for downloading GUI can not dynamically accommodate new sensors. All datasets stored at one location

OpenDAP Replay System Use DAS, DDS information to dynamically generate interface Use URL constraints to search based on any data type Use URL constraints to customize downloaded datasets Multiple servers may provide datasets

OpenDAP Replay System

Summary Introduced the OpenDAP protocol, it’s history, architecture and current uses Quick OpenDAP demo Case Study: Dive Replay System Looked at existing system and its faults Discussed a new OpenDAP-based systsm and its advantages

Questions?