[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: What does "optional" mean?
Costello, Roger L. scripsit: > I've listed three possible meanings of "optional": > > -- In the first meaning, it indicates: of-lesser-importance. > > -- In the second meaning, it indicates: irrelevance. > > -- In the third meaning, it indicates: lack-of-knowledge. In the subset of $EMPLOYER's schemas that I've worked on, known as the entity schemas, each document represents the state of our knowledge about a real-world object such as Barack Obama, the U.S. House of Representatives, or William Kunstler. These documents would be validated by the GovernmentOfficial, LegislativeBranch, and Attorney schemas respectively. (Obama might also be represented by an Attorney document, which would be a separate document but with the same unique object ID assigned by us.) There are three use cases for these documents, indicated by an attribute on the root element: publish, identify, and discrepancy. In publish, we are sending a customer everything we know. In identify, a customer is sending us what he knows (for example, a name or an id) and we are replying with what we know, hopefully a superset of it. In discrepancy, a customer is sending us what he believes to be right, and we verify it (manually, not by computer) and adjust the parts we have wrong. To serve all these use cases, we use schemas in which every element at every level is optional. In publish, we can only publish what we have, from which anything (other than the unique object ID, also a root-element attribute) might be missing. In identify, we cannot say in advance exactly what information a customer might have that would suffice for identification (not necessarily unique identification; the customer might know only a surname, and then we send back all Person documents with that surname). In discrepancy, we require our unique object ID to be sent back, along with whatever subset of the information is asserted to be wrong. > So what does "optional" really mean? For the entity schemas, it firmly means your third option, lack of knowledge. However, in the content schemas which we use for actual documents, like texts of laws, it means irrelevance: the schema may allow for subsections, but the document may or may not have them. -- Henry S. Thompson said, / "Syntactic, structural, John Cowan Value constraints we / Express on the fly." cowan@ccil.org Simon St. Laurent: "Your / Incomprehensible http://www.ccil.org/~cowan Abracadabralike / schemas must die!"
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