As an appendix to the Semantic Scratchings post, a couple of additional diagrams to illustrate the process.
The first shows a simple graph of a mythical contact. There are additional properties that can be added, but it shows the core split into organisation, vCard, and FOAF relationships.
The second shows the workflow from entering contact details, to displaying query results on a web page. The icons are standard UML analysis boundary, control, and entity classes, and it also shows the domains in which each entity sits.
I hope it gives some idea of the steps I’m using. Not optimised, certainly, but it’s reasonably decoupled across standard protocols and APIs.