- From: Mork, Peter D.S. <pmork@mitre.org>
- Date: Wed, 28 Sep 2005 14:49:43 -0400
- To: "Melissa Cline" <cline@pasteur.fr>, "Wafik Farag" <Wafik@Farag.net>
- Cc: <helen.chen@agfa.com>, <public-semweb-lifesci@w3.org>, <public-semweb-lifesci-request@w3.org>
>One beauty of SW is that the "over-arching layer" doesn't really need to >know any details about the sub-domain ontologies. This is the classic >contrast between XML and RDF: XML data is tree-structured, while RDF data >is structured as a DAG. If you combine two different DAGs, the result is >still a DAG. But if you combine two trees, the result is not necessarily >a tree: if you join on the leaves, you end up with a structure with two >roots. To turn this into a tree again, you have to go through "XML hell" >and rebuild the whole structure. > RDF is a directed, edge-labeled graph; it is not acyclic. Moreover, if you combine two DAGs, you are not guaranteed to get a DAG. For example, consider tree T (which is a DAG). Now consider T', in which every edge in T has been reversed (also a DAG). If you combine T and T', the result is cyclic (assuming T contains at least one edge). Peter
Received on Wednesday, 28 September 2005 18:51:05 UTC