MODster Project
MODster Description
MODster is a distributed, decentralized inventory server for Earth science data granules (standard units of data content and structure.) MODster connects data granule users (people who know which specific granule they want, but who don't know who has it or how to get it) with data granule providers (people or institutions that keep granules accessible online.)
- If you're a provider, you can tell MODster which granules you have and where they live (i.e., their URLs.)
- If you're a user, you can ask MODster for a granule, and it will transparently redirect your request to whomever has it.
The key to making this work is a standard granule namespace . A granule namespace is a naming convention that associates particular names with particular granules, regardless of where those granules live. Different Earth science data products have their own granule namespaces.
Example: in the MODIS granule namespace, the granule name
MOD43A2.A1998365.h5.v8.001.1999001090020.hdf
always refers to the first version of the Level 3 16-day Bi-directional Reflectance Distribution Function product for 31 December 1998, at the 5th horizontal tile and 8th vertical tile, generated on 01 January 1999 at 9:00:20 AM.
A MODster URL is simply a standard way of referring to a data product namespace and one of its granules. MODster URLs have the general form:
http://server/namespace/granule
where granule is a granule name that conforms to a granule namespace, namespace is a MODster namespace, which is the name of a granule namespace whose conventions are known to MODster, and server is a MODster server, which is an HTTP server that can redirect namespace/granule requests to granule providers.
Example: If http://essw.bren.ucsb.edu/modster is a MODster server, and MODIS is the MODster namespace for MODIS granules, then a MODster URL for the previously-mentioned MODIS granule would be:
http://essw.bren.ucsb.edu/modster/MODIS/MOD43A2.A1998365.h5.v8.001.1999001090020.hdf
A MODster URL with no granule component gets a description of the MODster namespace, its authority (the persons or institutions responsible for documenting and maintaining the naming convention), and also any services for that MODster namespace that the MODster server supports. (These services aren't standardized, yet...)
Any similarity between MODster and certain well-known Internet-based music-sharing schemes is purely intentional...
DODster Extension
DODster is an extension of MODster, providing a user with the ability to use DODS processing on any data retrieved through MODster. DODS, the Distributed Oceanographic Data System, allows you to access data by passing it through a DODS server (URL-based) and then display the contents of a data file in different formats.
DODster itself takes care of the URL naming conventions so that the user has only to select which type of DODS operation should be performed so that the proper output may be displayed. For more detailed info on different types of DODS processing, see the DODS Homepage.
In order to use DODster, a data file must be entered in the DODster data file selection box (in the MODster tool). If that file exists in the DODster database (if it has been registered through DODster), then a page will be displayed which shows all the processes which can be performed on that dataset.
Example: If http://essw.bren.ucsb.edu/modster is a MODster server, and MODIS is the MODster namespace for MODIS granules, then to get to the DODster section, go to the URL:
http://essw.bren.ucsb.edu/modster/MODIS/
From this page, type in the name of the MODIS dataset you wish to find and perform DODS operations on in either the DODsterDirect or DODsterProxy selection areas. If you do not know the whole name of the dataset, matching will be performed to find a list that complies with any partial requests.
DODsterDirect contains a list of datasets on which DODS processing can be performed locally. That is, the DODS server which is processing the desired data is on the same web server as the data itself.
DODsterProxy contains a list of datasets on which DODS processing can be performed remotely. That is, a DODS provider may specify a list of data types that they will process through their local DODS server for some other data provider. This allows DODS processing even for datasets which reside at a location which does not provide DODS server capabilities.
Once a dataset has been selected, the list of possible DODS processing operations will be displayed, and by clicking on an operation type, a user brings up the specified results for that dataset.
Any similarity between DODster and certain well-known Internet-based music-sharing schemes is purely intentional...
MODster is being developed by the ESSW ESIP with support from NASA and the ESIP Federation. Special thanks to James Gallagher for his help in adding DODsterProxy capabilities to DODS.
