Semantic Web and Resource Description Framework
Need defined
HTML can only say that the span of text "ID586172" is something that should be positioned near "Acme Gizmo" and "$199", etc. There is no way to say "this is a catalog" or even to establish that "Acme Gizmo" is a kind of title or that "$199" is a price. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items perhaps listed on the page.