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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. - PowerPoint PPT Presentation
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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://dap_server/cgi-bin/nph-dods/data/dataset1– 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.– http://…/data.dods?date&time&temp
• Constraints specify search criteria.– http://…/data.dods?temp>100&temp<175
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
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
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?
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