What is an Attachment?

Here's our current definition of an attachment:

• A resource that is related to another resource and adds supplemental information
• For example:
  • A screen-shot attached to a Change Request
  • An office document attached to a Requirement

How should attachments work?

Attachments are Resources. A Resource links to its Attachments.

• Attachment should be created via POST
• Attachment should have URI
• Resource links to its attachments

One issue: which spec will define the attachment link property, Core or domains?

Use case #1: Consumer associates Attachment with Resource

The consumer does the work: creating the Attachment if necessary and adding the link to the Resource being attached to.

WebSequence Diagrams page

Consumer->Service: POST attachment to be added
Service->Consumer: gets back URI of attachment 
Consumer->Resource: GET resource to be attached to 
Consumer->Resource: PUT back resource with new link to attachment

Nothing new here. This is how you'd expect things to work with HTTP and RDF.

Some notes:

• Consumer may create Resource via POST (as shown above) or Consumer may use an existing Resource as the Attachment, if the Provider allows that
• Provider may require that all Attachments be created via Provider’s Creation Factory, thus disallowing using of existing Resources

Use case #2: Consumer displays Resource and list of Attachments

Consumer can display Resource and list of attachments because, in addition to links to Attachments, Resources may contain:

• Property values which are links to Attachments
• Property values about the Attachments
• Property values about the Attachments links

Either Provider or Consumer may add those properties.

A Consumer knows which property values are links to Attachments and how to find properties about each, so it can easily display a list of Attachments. Nothing new here either, just plain RDF

Use case #3: Consumer gets and updates an Attachment

To implement this use case, the Consumer gets a Resource, picks the Attachment to update, gets the Attachment and then puts back the updated Attachment. For example, here a Consumer gets and updates an image Attachment.

WebSequence Diagrams page

Consumer->Resource: GET
note left of Consumer: picks Attachment URI
Consumer->Attachment: GET on Attachment URI
Attachment->Consumer: sends back Attachment
note left of Consumer: edits Attachment image
Consumer->Attachment: PUT new image
Consumer->Resource: PUT with updated properties about Attachment