The topics covered on this page include information regarding the disovery of Earth Science data contained within ECHO's holdings . It is the responsiblity of the Client Partner to expose the ECHO discovery capabilities through the usage of the ECHO API..
The information provided is broken up into the following topic areas:
The ECHO kernel facilitates both synchronous and asynchronous data discovery mechanisms. Both the discovery queries and results may be saved within ECHO for future use by an ECHO end user. If an asynchronous query is performed, the user will be provided with a unique query identifier which may be used to poll for query results. The image found below shows the ECHO query workflow.
When initially submitting a query, a maximum result size and iterator size are provided. These values are used to limit the total amount of items which will be returned, and how many will be returned at one time. After a query has returned, the query results may be further accessed through the usage of a 'cursor.' The following list contains the type of results which may be gathered through data queries.
For a complete overview of the ECHO Query workflow, please refer to:
In order to facilitate data discovery, ECHO utilizes the Independent Information Management Subsystem (IIMS) Alternative Query Language (AQL). This is referred to commonly as the ECHO "AQL". This query language allows clients to discover data based upon a selection of metadata fields which are contained within the ECHO data holdings.
For a complete overview of the ECHO Alternative Query Language, please refer to:
The XML messages passed in and received from the ECHO API interface conform to a set of Document Type Definitions (DTDs) that correspond to the particular messages involved. A client partner must use these DTDs in creating the XML messages to query and interpret query results:
The following items outline some common areas which Client Partners should be aware of while discovering data in ECHO. For a complete overview of data discovery, please refer to:
ECHO Data Partners may create permissioned access to certain collections and granules within their data holdings. These restructions are applied to specific groups of ECHO users and access to permissioned data is dependent upon membership in the defined user groups. Users who are not a member of a group will not be able to access the data restricted to its members. In some circumstances, the Data Partner may allow access to a collection, but not to its granules. If you have a need to access specific data, please contact the Data Partner's user-services contact in order to discuss your needs.
In order to reduce the time required to discover data within the ECHO holdings, it is strongly encouraged for ECHO Client applications refrain from performing queries which return the total number of items that fulfill the query. The "Hits" result type will perform this type of query. Also, ECHO Client applications should encourage users to use a reasonable value for "Max Results" when generating a query.