Utilization of data access and manipulation in conceptual schema definitions

摘要

The basic idea of this approach is to use data access and manipulation functions in data definition, such that testing a given individual data object on its conformance to data definition is done by running a (finally boolean) procedure against it. In essence, schema entries (i.e. definitions, declarations, etc.) are viewed as expressions of predicate logic where the individuals are obtained by the execution of data manipulation operations which include a rather general information selection technique or conceptual access method.Selection of information constructs in databases usually adopts a technique closely tailored to the specific “data model”. It is one of the intentions of this paper to demonstrate the common principles behind the variety of selection techniques by a uniform approach which comprises the selection features of most of the database management systems and makes them comparable.At the level of information structure a kind of “geography” is introduced into a database, which allows to distinguish the same information construct (record, file, segment, item, coset, tuple,…) in distinct information contexts or at distinct conceptual locations called “spots”. By definition, every spot (“construct in/with context”) exists only once in a given database. In combination with some basic operators a logical addressing mechanism has been designed, which follows the context of a construct to identify it within this very context. This algorithm turns out to be a general vehicle to locate a construct at a spot, independently of whether the database has a relational, network, hierarchical or any other appearance.The method of context directed addressing along with pertinent operators allows in a very general way—i.e. neither biased nor restricted to a “data model”—to define types of information constructs and of construct transitions as is required in a conceptual community schema. This is demonstrated through examples of schema entries with rather complex cross-consistency conditions and additional transition rules called persistency conditions. The examples also intend to give an idea of the minimum support to be expected from any future conceptual schema language.