WCS-UC1.0

Point Of Contact: Mr. Patrick West

Description

WCS GetCoverage request with a pre-built response

Goal

The goal of this use case is to provide an end-to-end request/response to a GetCoverage request. It is intended to get the OLFS and BES involved in the WCS system, with the BES providing the response to this request.

Summary

The primary actor, a person sitting at a computer, enters a pre-defined URL into their browser for a GetCoverage request and receives a Coverages document that contains a Coverage element that has a Reference element that links to a target NetCDF-CF response to be saved to their local disk.

We are attempting to coordinate communication between the OLFS and the BES in this WCS system, with a request coming in to the OLFS from the users browser, the OLFS formulating the request to the BES, and the BES responding to that request with a Coverages document containing a Reference element with the the link to the target NetCDF-CF file.

The request and the response will be pre-defined. In other words, the user won’t be browsing around the catalogues or making GetCapabilities or DescribeCoverage calls and the BES will have a pre-built response, which is a a Coverages document (file) containing a Reference element with the the link to the target NetCDF-CF file.

Actors

Primary actor – user sitting at browser
Secondary actor – OLFS – receives the request from the browser
Secondary actor – BES – receives request from the OLFS and responds to the request
Secondary actor – pre-built Coverages document saved as a file.
Secondary actor – pre-built target NetCDF-CF file

Preconditions

Using the WCS 1.1.2 specification
The request URL is a known request, provided for this use case
The request parameters are in KVP format
The request parameters version, request type and Id are already known
The domain subset is in WGS84 BB, Circumscribe N.J. on grid vertices
The temporal subset is optional and will be left out
The range subset is optional and will be left out
The target response file format will be NetCDF-CF
The response from Hyrax will be a Coverages document containing a Coverage with a Reference element containing a link to the pre-built NetCDF file.

Triggers

The user enters the provided URL representing the GetCoverage request into the browser

Basic Flow

OLFS receives the request
OLFS parses the KVP parameters from the request URL including the version, request type, and id
OLFS sets the domain subset (bb)
OLFS sets the temporal subset (optional ???)
OLFS sets the range subset (optional ???)
OLFS sends the request to the BES as an XML document
The BES parses the XML document representing the GetCoverage request
The BES matches the coverage id (and other input)
The BES returns a pre-built Coverages document that a Coverage element with a Reference containing a link to the pre-built response file, which is in NetCDF-CF format
The OLFS returns the Coverages document to the user
The user receives the response, and locates the Coverage containing the Hyrax URL to the target response file. The user takes that URL and enters it into their browser.
The OLFS sends the request to the BES to stream the target response file back to the user. This functionality already exists (get stream for definition).

Alternate Flow(s)

Error Flow (OLFS)

OLFS receives the request
OLFS attempts to parse the KVP parameters from the request.
The parsing encounters a bad request (based on the 1.1.2 specification), or …
The OLFS fails to connect to, or the connection drops to, the BES in Basic Flow step 6, or …
The OLFS fails to connect to, or the connection drops to, the BES in Basic Flow step 12 …
OLFS builds a WcsException and returns it to the user.

Error Flow (BES)

See Basic Flow steps 1-7
The BES fails to match the coverage id or some other input (Unsupported operations, CRS mismatch, etc.), or …
The BES fails to access the pre-built coverage response document, or …
In Basic Flow step 9, the BES fails to access the file containing the pre-built Coverages document.
The BES builds a WcsException element and returns it to the user via the OLFS.

Post Conditions

None.

Activity Diagram

Notes

Question:

Will the BES be streaming the response file back to the OLFS, and then on to the user? Or will the BES return a URL to the response file that the user will then click on to download?

Answer: The BES will return a link to the target file, not stream the file back. The user will then be able to click on this link and save it to their local disk.

Resources

Data

Data	Type	Characteristics	Description	Owner	Source System
HF Radar Data	Remote netCDF-CF	One Time Slice	Contains one time slice.	Dan Holloway	dev1.opendap.org

Application Services

Application	Owner	Description	Source System
OLFS	OPeNDAP	OPeNDAP Hyrax front end service – receives request from the user’s browser	dev1.opendap.org
BES	OPeNDAP	OPeNDAP Hyrax back-end server – receives request from OLFS and responds with link to target NetCDF-CF file	dev1.opendap.org

Other Resources

Resource	Owner	Description	Availability	Source System
(sensor name)	Organization that owns/ manages resource	Short description of the resource	How often the resource is available	Name of system which provides resource

Butte Meeting Notes

Use Case 1 - GetCoverage

Precondition

Version, Request Type, Id already known
KVP request to OLFS
Domain Subset
BB (WGS84 BB) Circumscribe N.J. on grid verteces
Temporal is optional and will be left out
Range Subset: optional
Format: NetCDF-CF

Trigger

Request from user

Sequence of Events

Request to OLFS/Handler
KVP parsing
- Request Type, Version, Id
Set Domain Subset (bb)
Set Temporal Subset
Set Range Subset
Generate coverage response
- Match id and other stuff
- ask BES for the response
- BES returns pre-built response