Re: [Waterken-server] org.yurl.Author schema

[Tyler C. <ty...@wa...>]

On Feb 2, 2006, at 3:21 PM, Sandro Magi wrote:
> I'm making a little headway with these schemas. I'm looking at=20
> org.yurl.Author at the moment since it seems to encapsulate most of=20
> elements: Link, Embed, methods, etc.

Yes, the org.yurl.Author object is a good example to study to learn=20
about schemas.

> Here is my current understanding:
>
> =A01. if an object has an explicit schema (ie. =
yurl.org/wiki/Page.xml),=20
> then it does not require the schema attibute on individual nodes; ie.=20=

> a Page only requires the 'schema' in the top-level node to identify it=20=

> as a Page, whereas an object without a predefined schema would need a=20=

> 'schema' attribute on each node.

The general rule is that the schema MUST be explicitly stated on the=20
node, unless it can be unambiguously determined based on the schema and=20=

branch of the containing node. For example, the=20
<http://yurl.org/Author> schema specifies the expected schema for the=20
'topic' branch as <http://web-calculus.org/string/String>. If you do a=20=

"View Source" on one of the wiki editors, you will see that the schema=20=

attribute on the 'topic' branch is not specified since the referred to=20=

node is in fact a string. The recipient of the wiki editor node can=20
unambiguously determine the schema for the 'topic' node since the=20
schema for the top level node (the 'doc' branch) is specified and that=20=

schema provides the expected schema for the 'topic' branch.

> =A02. a yurl.org/Author also has an explicit/pre-defined schema, but =
the=20
> method definitions seem to be "overridden" in the actual doc returned=20=

> to the client; in yurl.org/Author, 'revoke' is defined as a=20
> yurl.org/Author-revoke, but the actual returned doc has a=20
> http://web-calculus.org/pointer/Link in its place, and a schema=20
> "override" to convey this information.

The schema for pointer nodes is always explicitly stated. This feature=20=

enables writing of a web-calculus spider which could traverse an=20
arbitrary graph of nodes, without needing to know the schema of any=20
encountered node.

For example, such a spider could make a backup of your yurl.net wiki.

> So this leads to a question:
>
> In this case, the Author methods translate into a set of=20
> http://web-calculus.org/pointer/Link in the returned document. Is this=20=

> necessarily the case for all methods?

Yes.

>  Can a method be returned as an http://web-calculus.org/pointer/Embed=20=

> instead?

No.

>  If so, what determines the Author methods should be of type Link in=20=

> this particular case?

An Embed link means: "replace this pointer node with the node at this=20
address". For a method, the client needs to retain the pointer so that=20=

POST requests can be sent along it. So an object method is always=20
represented as a Link, which means: "replace this pointer node with a=20
link to the specified address".

Tyler

---
The web-calculus is the union of REST and capability-based security:
http://www.waterken.com/dev/Web/