Although XML Document Type Definitions provide a mechanism for specifying, in machine-readable form, the syntax of an XML markup language, there is no comparable mechanism for specifying the semantics of an XML vocabulary. That is, there is no way to characterize the meaning of XML markup so that the facts and relationships represented by the occurrence of XML constructs can be explicitly, comprehensively, and mechanically identified. This has serious practical and theoretical consequences. On the positive side, XML constructs can be assigned arbitrary semantics and used in application areas not foreseen by the original designers. On the less positive side, both content developers and application engineers must rely upon prose documentation, or, worse, conjectures about the intention of the markup language designer -a process that is time-consuming, error-prone, incomplete, and unverifiable, even when the language designer properly documents the language. In addition, the lack of a substantial body of research in markup semantics means that digital document processing is undertheorized as an engineering application area. Although there are some related projects underway (XML Schema, RDF, the Semantic Web) which provide relevant results, none of these projects directly and comprehensively address the core problems of XML markup semantics. This paper (i) summarizes the history of the concept of markup meaning, (ii) characterizes the specific problems that motivate the need for a formal semantics for XML and (iii) describes an ongoing research project -the BECHAMEL Markup Semantics Project -that is attempting to develop such a semantics.
We examine the conceptual model of the "bibliographic universe" presented in IFLA's Functional Requirements for Bibliographic Records (FRBR) and argue, applying ontology design recommendations proposed by N. Guarino and C. Welty, that three of the four Group 1 entity types might be more accurately conceptualized as roles. We show how this approach may generalize the solution to a previously identified puzzle regarding the FRBR entity type of XML documents and speculate as to the sorts of entities that might take on these roles. This view of bibliographic entities, that they are roles that other things have in particular social contexts is consistent with John Searle's notion of a cascade of social facts established through collective intentionality. We allow that even if our analysis is correct the current FRBR approach may be preferable as there are good reasons for "denormalized ontologies" that treat roles as types, particularly when the objective is not a general ontology, but a practical conceptual model.
Accurate chromosome segregation during mitotic division of budding yeast depends on the multiprotein kinetochore complex, Dam1 (also known as DASH). Purified Dam1 heterodecamers encircle microtubules (MTs) to form rings that can function as ''couplers,'' molecular devices that transduce energy from MT disassembly into the motion of a cargo. Here we show that MT depolymerization develops a force against a Dam1 ring that is sixfold larger than the force exerted on a coupler that binds only one side of an MT. Wild-type rings slow depolymerization fourfold, but rings that include a mutant Dam1p with truncated C terminus slow depolymerization less, consistent with the idea that this tail is part of a strong bond between rings and MTs. A molecularmechanical model for Dam1-MT interaction predicts that binding between this flexible tail and the MT wall should cause a Dam1 ring to wobble, and Fourier analysis of moving, ring-attached beads corroborates this prediction. Comparison of the forces generated against wild-type and mutant complexes confirms the importance of tight Dam1-MT association for processive cargo movement under load.depolymerization ͉ kinetochore ͉ laser trapping ͉ mitosis ͉ tubulin
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