In the simplest case, the semantics are implicit only. Meaning is conveyed based on a shared understanding derived from human consensus. A common example of this case is the typical use of XML tags, such as price, address, or delivery date. Nowhere in an XML document, or DTD or Schema, does it say what these tags mean [Cover 98]. However, if there is an implicit shared consensus about what the tags mean, then people can hardwire this implicit semantics into web application programs, using screen-scrapers and wrappers. [...] The disadvantage of implicit semantics is that they are rife with ambiguity. People often do disagree about the meaning of a term. For example, prices come in different currencies and they may or may not include various taxes or shipping costs. The removal of ambiguity is the major motivation for the use of specialized language used in legal contracts. The costs of identifying and removing ambiguity are very high.