1. Salzburg Research IOT Avatar Salzburg Research IOT
  2. Untitled project
  3. lmf

Wiki

Clone wiki

lmf / Usage-Resource-Interaction

View History

How to create, update, retrieve and delete resources and associated content and metadata using the Linked Media / Linked Data principles

The LMF resource service allows to create, retrieve, update and delete individual resources and the metadata associated with them (see also LinkedMediaPrinciples).

To interact with resources, you need a REST client that is capable of issuing POST, PUT, GET and DELETE commands to remote resources. A very basic command line tool for this is cURL ([http://curl.haxx.se/download.html]).

The following series of commands creates, retrieves, updates and deletes the resource http://localhost:8080/LMF/resource/1234:

Create Resource

Command: 

curl -i -X POST http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 201 Created
Server: Apache-Coyote/1.1
Location: http://localhost:8080/LMF/resource/1234
Content-Length: 0
Date: Wed, 18 May 2011 12:17:12 GMT

The result code of 201 indicates that the resource has been created. If the resource already exists, a "302 Found" will be returned.

Upload Metadata

The server decides based on the "Content-Type" header how to process data sent with the request. To upload metadata, the Content-Type should be of the form "type/subtype; rel=meta". Examples: - application/rdf+xml; rel=meta - text/rdf+n3; rel=meta - ...

Command: 

curl -X PUT -i -H "Content-Type: text/rdf+n3; rel=meta"  \
     -d '<http://localhost:8080/LMF/resource/1234> <http://www.w3.org/2000/01/rdf-schema#label> "Test Resource".' \
     http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 303 See Other
Server: Apache-Coyote/1.1
Location: http://localhost:8080/LMF/meta/text/rdf+n3/1234
Content-Length: 0
Date: Wed, 18 May 2011 12:33:32 GMT

The result indicates that we have to redirect the request to the location http://localhost:8080/LMF/meta/text/rdf+n3/1234 . Note that many clients will not perform an automatic redirect properly, since they rewrite the method from PUT to GET. So it is preferrable to manually execute the redirect:

curl -X PUT -i -H "Content-Type: text/rdf+n3; rel=meta" \
     -d '<http://localhost:8080/LMF/resource/1234> <http://www.w3.org/2000/01/rdf-schema#label> "Test Resource".' \
     http://localhost:8080/LMF/meta/text/rdf+n3/1234

Result: 

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Length: 0
Date: Wed, 18 May 2011 12:38:30 GMT

Upload Content

The server decides based on the "Content-Type" header how to process data sent with the request. To upload content, the Content-Type should be of the form "type/subtype; rel=content". Examples: - text/html; rel=content - text/plain; rel=content - image/jpeg; rel=content - ...

Command: 

curl -X PUT -i -H "Content-Type: text/plain; rel=content" \
     -d 'This is textual content of the resource' \
     http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 303 See Other
Server: Apache-Coyote/1.1
Location: http://localhost:8080/LMF/content/text/plain/1234
Content-Length: 0
Date: Wed, 18 May 2011 12:47:16 GMT

Again, we manually perform the redirect, this time to http://localhost:8080/LMF/content/text/plain/1234:

curl -X PUT -i -H "Content-Type: text/plain; rel=content" \
     -d 'This is textual content of the resource' \
     http://localhost:8080/LMF/content/text/plain/1234

Result: 

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Length: 0
Date: Wed, 18 May 2011 12:47:48 GMT

Retrieving Metadata

The server decides based on the "Accept" header how to process data sent with the request. To retrieve metadata, the Accept should be of the form "type/subtype; rel=meta". Examples: - application/rdf+xml; rel=meta - text/rdf+n3; rel=meta - ...

When issuing the GET request, the server again returns a redirect. Since the request is a GET, it is safe to let curl automatically follow the redirect (-L):

Command: 

curl -X GET  -L -i -H "Accept: application/rdf+xml; rel=meta" \
     http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 303 See Other
Server: Apache-Coyote/1.1
Location: http://localhost:8080/LMF/meta/application/rdf+xml/1234
Content-Length: 0
Date: Wed, 18 May 2011 12:51:21 GMT

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Link: <http://localhost:8080/LMF/content/text/plain/1234>;type=text/plain;rel=content
Content-Type: application/rdf+xml
Content-Length: 298
Date: Wed, 18 May 2011 12:51:21 GMT

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="http://localhost:8080/LMF/resource/1234">
    <rdfs:label>Test Resource</rdfs:label>
</rdf:Description>

</rdf:RDF>

Retrieving Content

The server decides based on the "Accept" header how to process the data requested. To retrieve content, the Accept should be of the form "type/subtype; rel=content". Examples: - text/html; rel=content - text/plain; rel=content - image/jpeg; rel=content - ...

When issuing the GET request, the server again returns a redirect. Since the request is a GET, it is safe to let curl automatically follow the redirect (-L):

Command: 

curl -X GET  -L -i -H "Accept: text/plain; rel=content" \
     http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 303 See Other
Server: Apache-Coyote/1.1
Location: http://localhost:8080/LMF/content/text/plain/1234
Content-Length: 0
Date: Wed, 18 May 2011 12:58:07 GMT

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Links: ...
Content-Type: text/plain
Content-Length: 39
Date: Wed, 18 May 2011 12:58:07 GMT

This is textual content of the resource

The "Links:" header gives pointers to available alternative formats for the resource.

Deleting a Resource

A resource is deleted using the DELETE method:

Command: 

curl -i -X DELETE http://localhost:8080/LMF/resource/1234

Result: 

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Length: 0
Date: Wed, 18 May 2011 12:38:30 GMT

Updated