URI

A uniform resource identifier (URI) is a standard way of referencing elements, objects, files, and so on.

URIs

The basic URI syntax is:

scheme://authority/path?query#fragment

Examples of URIs include

file:///home/sthomas/models/cube.dae
file:///C:/models/sphere.dae#myGeometry
http://www.google.com/

The following table shows the breakdown of each URI component in the previous examples.

URI	Scheme	Authority	Path	Query	Fragment
file:///home/sthomas/models/cube.dae	file	-	/home/sthomas/models/cube.dae	-	-
file:///C:/models/sphere.dae#myGeometry	file	-	/C:/models/sphere.dae	-	myGeometry
http://www.google.com/	http	www.google.com	-	-	-

URI references

Many XML-based formats (including COLLADA) primarily use URI references. URI references are a superset of URIs. A URI reference is either a URI or a relative reference. A URI reference is a relative reference if it doesn't include the scheme: prefix. Before a relative reference can be used, it must be converted to a URI in a process called reference resolution. The reference resolution algorithm combines the relative reference with a base URI to form the full URI that is then used by the application.

Below are some examples of URI references. These examples are full URIs (since they include the scheme: prefix). Since these are full URIs, they can be used directly by an application without being resolved.

file:///home/sthomas/models/cube.dae
file:///C:/models/sphere.dae#myGeometry
http://www.google.com/

Here are some more examples of URI references. Since these references don't include a scheme: prefix, they're relative references and will need to be resolved before they can be used by an application.

/home/sthomas/models/cube.dae
/C:/models/sphere.dae#myGeometry
../../image.jpg
#redMaterial

Relative reference resolution

A relative reference is combined with a base URI to yield a full URI in a process called reference resolution. The full algorithm is given here.

Assuming a base URI of

file:///C:/A/B/C/D/doc.dae

here are some examples of how relative references would be resolved:

Relative Reference	Resolved URI
./path/document.dae	file:///c:/A/B/C/D/path/document.dae
../../../path/document.dae#elementID	file:///A/path/document.dae#elementID
/c:/path/document.dae#Light01	file:///c:/path/document.dae#Light01
c:/path/document.dae	file:///c:/A/B/C/D/c:/path/document.dae

The last example probably doesn't resolve the way the author intended. An initial "/" character as in the third example is necessary to make the reference an absolute path. That way the path from the base URI is discarded.

See also

• Using URIs in COLLADA
• DOM guide: Resolving URIs

External links

• The URI spec
• URI article on Wikipedia
• Discussion of URI file scheme