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Representing Constraints by Means of Graphs
In the context of temporal semistructured data, it is important to store the time dimension
related to the represented information, and to manage in a correct way the
considered time dimension. At this aim, a set of constraints must be defined. In this
work, we consider the valid time dimension, thus the defined constraints must be
able to guarantee that the history of the given application domain is consistent.
In our proposal, it is possible to define two different categories of constraints for
valid time values of nodes and edges: basic constraints must be satisfied by every
GEM graph; domain-dependent constraints are further constraints, which can be
defined either for some specific nodes and edges or for the whole graph for a specific
application domain. Domain-dependent constraints are strictly related to the
semantics of the represented objects and relationships.
As an example of basic constraints, at a specific time instant, between two nodes
it cannot exist more than one edge representing the same relation (Combi et al.,
2004).
The graphical formalism used in the following constraints has been described in
Damiani, Oliboni, Quintarelli, and Tanca (2003) and Oliboni (2003): a constraint
is composed by a graph, which is used to identify the portions of a semistructured
graph where the constraint has to be applied, and a set of formulae, which represent
restrictions imposed on those subgraphs.
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