HELM Web Services

Introduction

The following describe the Heliophysics Event List Manager (HELM) RESTful Web services.

Target Audience

This document assumes that the reader is familar with RESTful Web service and Hypertext Transfer Protocol (HTTP) technologies.

Overview

This section contains an overview of these Web services.

Entity-Body Representations

The HTTP entity-body for both the request and response messages of these services is described by a W3C XML schema document. The detailed description of each service describes the specific XML element from the schema that is an entity-body for the specific request or response message of the service. In addition to the XML representation of the entity-body, all the services can return the entity-body in a mapped (with root unwrapping) JSON representation of the XML object. A client can express their preference for a specific entity-body representation (XML or JSON) by setting the HTTP accept header (to "application/xml" or "application/json").

Error Responses

This section provides a general description of error responses (i.e., a reponse with a code other than 200) that may be returned by any of the web services. More details about the error response of specific services are provided in the specific service's description.

Any entity-body returned within an error response will be XHTML (or a JSON representation of XHTML) that contains a more detailed description of the error. Whether the entity-body is XHTML or JSON depends upon the HTTP Accept header in the request. Not all error responses will contain an entity-body. A client may simply display the XHTML or access the more detailed error message within the XHTML at //p[class='ErrorMessage']/text() and //p[class='ErrorDescription']/text().

Note that error responses may also be generated by software components other than the web services software described here in response to requests intended for these web services. For example, a request with an invalid URI path may result in a response (e.g., 404) that is generated by the application server instead of by the web service software. In fact, different invalid URI paths may result in an error response being generated by a proxy server, the web application server, the web service framework, or web service implementation itself. The entity-body in an error response will vary depending upon the software component that generates the response. A client must be prepared to deal with these differences. To diagnose a 404 response generated by the Jersey framework, the client should add an


X-Jersey-Trace-Accept

HTTP request header with any value to the request. This will cause the 404 response to have


X-Jersey-Trace-nnn

headers that will describe the failed attempts to match the request to a Web service implementation.

The above description of an entity-body in an error response only describes those generated by the web service implementation itself. At the time this documentation was written, the entity-body returned in an error response from both these web services and the application server hosting them were similar. The

//p[class='ErrorMessage']/text()

value described above is accessible by //p[2]/text() in the error response from both these web services and their hosting application server. Likewise, the

//p[class='ErrorDescription']/text()

value described above is accessible by //p[3]/text() in the error response from both these web services and their hosting application server.

General Example Clients

Shell Script Example. This example should run on most Unix-like (e.g., Linux, Mac OS X, Solaris, etc.) platforms that have curl, xsltproc, and xmllint. Here is the output from running the example.
Java example utilizing java.net.HttpURLConnection.
Java example utilizing the Jersey client API (com.sun.jersey.api.client).
helm2simileEventSource.xslt. An XSLT transformation to produce a Simile Widgets XML Timeline Event Source from a HELM Eventlist.

Web Services

The table below summarizes the services which are available. The table contains links to more detail descriptions of each operation.

Web Services
Operation	Implementation	Details
Get WADL	OPTIONS /	Details
Get About Info.	GET /about
Get Privacy Info.	GET /privacy
Get Terms of Use Info.	GET /termsOfUse
Get an Eventlist	GET /eventlists/{listname: [a-zA-Z][a-zA-Z_0-9]*}	Details
Search Eventlists	GET /eventlists?keyword={keyword}&xpathp={xpathp}	Details
Eventlist Union	GET /union?listUrl={listUrl}	Details
Eventlist Intersection	GET /intersection?listUrl={listUrl}	Details
Shift Times of Eventlist	GET /shiftTimes?quantity={quantity}&listUrl={listUrl}	Details
Shift Times of Eventlist	POST /shiftTimes?quantity={quantity}	Details
Adjust TimeSpans of Eventlist	GET /adjustTimeSpans?quantity={quantity}&listUrl={listUrl}	Details
Adjust TimeSpans of Eventlist	POST /adjustTimeSpans?quantity={quantity}	Details

Get WADL

This service provides the Web Application Description Language (WADL) for these Web services.

Example

Below is an example client request to this service and the results.

$ curl --request OPTIONS http://helm.gsfc.nasa.gov/WS/helm/1/ | xmllint --format -

Get About

Get Privacy

Get Terms Of Use

Get an Eventlist

Retrieves the specified Eventlist.

HTTP Method		GET
URI		/eventlists/{listname:[a-zA-Z][a-zA-Z_0-9]*}
Significant Request Headers	Accept	application/xml
	Accept	application/json
	If-Modified-Since
Request Entity	none
Significant Response Headers	Last-Modified
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200	Ok
	304	Not Modified
	404	Not Found

Where:

{listname} is the name of the Eventlist. The name must conform to the regular expression [a-zA-Z][a-zA-Z_0-9]*.

Search Eventlists

Searchs all Eventlists for those that satisfies the given criteria and returns a description those Eventlists.

HTTP Method		GET
URI		/eventlists?keyword={keyword}&xpathp={xpathp}
Significant Request Headers	Accept	application/xml
		application/json
		application/xhtml+xml
Request Entity	none
Reponse Entity	Content-Type: application/xml	As specified by EventlistDescriptions in helm.xsd
	Content-Type: application/json	JSON representation of EventlistDescriptions in helm.xsd
	Content-Type: application/xhtml+xml	A very basic XHTML page with an unordered list (<ul>) containing the spase:Name values and an href link to the actual Eventlist. This is intended primarily for debugging and not expected to be very useful for general clients.
Most Likely Response Codes	200
	400
	404

Where:

{keyword} is an Eventlist/spase:Keyword value that selects the desired eventlist.
{xpathp} is any XPath 2.0 expression that selects the desired eventlist. For example, "//spase:PhenomenonType[text()='GeomagneticStorm']" URL encoded as "%2F%2Fspase%3APhenomenonType%5Btext%28%29%3D%27GeomagneticStorm%27%5D" would retrieve all Eventlists with PhenomenonType==GeomagneticStorm.
Multiple keyword values are logically ANDed together.

Eventlist Union

Performs a union of the specified Eventlists and returns the resulting Eventlist.

HTTP Method		GET
URI		/union?listUrl={listUrl}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity	none
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{listURL} is a URL identifying the Eventlist for the union operation. At least two values must be provided.

Eventlist Intersection

Performs an intersection of the specified Eventlists and returns the resulting Eventlist.

HTTP Method		GET
URI		/intersection?listUrl={listUrl}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity	none
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{listURL} is a URL identifying the Eventlist for the intersection operation. At least two values must be provided.

Shift Times of Eventlist (GET)

Adds the specified quantity to each StartDate and StopDate within the given Eventlist and returns the resulting Eventlist.

HTTP Method		GET
URI		/shiftTimes?listUrl={listUrl}&quantity={quantity}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity	none
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{listURL} is a URL identifying the Eventlist for the time-shift operation.
{quantity} is an ISO 8601 Duration value that is to be added to each Eventlist/Event/TimeSpan/StartDate and Eventlist/Event/TimeSpan/StopDate value within the specified Eventlist. The Duration value may be positive or negative.

Shift Times of Eventlist (POST)

Adds the specified quantity to each StartDate and StopDate within the given Eventlist and returns the resulting Eventlist.

HTTP Method		POST
URI		/shiftTimes?quantity={quantity}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity		As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{quantity} is an ISO 8601 Duration value that is to be added to each Eventlist/Event/TimeSpan/StartDate and Eventlist/Event/TimeSpan/StopDate value within the specified Eventlist. The Duration value may be positive or negative.

Adjust TimeSpans of Eventlist (GET)

Symmetrically widens or narrows all TimeSpan values in the specified Eventlist by the specified quantity and returns the resulting Eventlist.

HTTP Method		GET
URI		/adjustTimeSpans?listUrl={listUrl}&quantity={quantity}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity	none
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{listURL} is a URL identifying the Eventlist for the TimeSpan-adjustment operation.
{quantity} is an ISO 8601 Duration value that is to widen/narrow each Eventlist/Event/TimeSpan value within the specified Eventlist. The Duration value may be positive or negative. Half of the Duration value is subtracted from the each Eventlist/Event/TimeSpan/StartDate value and half of the Duration value is added to the Eventlist/Event/TimeSpan/StopDate value.

Adjust TimeSpans of Eventlist (POST)

Symmetrically widens or narrows all TimeSpan values in the provided Eventlist by the specified quantity and returns the resulting Eventlist.

HTTP Method		POST
URI		/adjustTimeSpans?quantity={quantity}
Significant Request Headers	Accept	application/xml
Significant Request Headers	Accept	application/json
Request Entity		As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/xml	As specified by Eventlist in helm.xsd
Reponse Entity	Content-Type: application/json	JSON representation of Eventlist in helm.xsd
Most Likely Response Codes	200
	400
	404

Where:

{quantity} is an ISO 8601 Duration value that is to widen/narrow each Eventlist/Event/TimeSpan value within the specified Eventlist. The Duration value may be positive or negative. Half of the Duration value is subtracted from the each Eventlist/Event/TimeSpan/StartDate value and half of the Duration value is added to the Eventlist/Event/TimeSpan/StopDate value.

Questions/Comments

Questions or comments concerning these Web services should be sent to HELM Feedback.