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An XSDB model M is a set of partial mappings from names to values

M subset of (NAMES --> VALUES)NAMES are strings (with restrictions) and VALUES may be strings, byte sequences, integers, floats or IDs. ID's are a special type of string which represents someinformation which is external to the system.

The "meaning" or denotation of an XSDB expression E is defined to be a set of models Models(E) where each model M in Models(E) is said to satisfy the expression E. An expression E1 is said to imply and expression E2 if every model of E1 is also a model of E2, and in this case E2 is said to be weaker than E1.

The xsdb model theory is intended to allow the representation of a wide variety of database organizations while maintaining relative simplicity. Standard tabular databases may be mapped into this representation by considering one of the NAMES to represent a table name. No size limits or type restraints are placed on the mappings in order to allow other sorts of data representations as well.