In Combi et al. (2004) the authors propose the Graphical sEmistructured teMporal
data model (GEM), which is based on labeled graphs and allows one to represent
in a uniform way semistructured data and their temporal aspects. In particular, they
focus on transaction time. The GEM data model is based on rooted, connected, directed,
labeled graphs. A GEM graph is composed by two kinds of nodes, complex
and simple nodes, which are graphically represented in different ways. Complex
nodes are depicted as rectangles and represent abstract entities, while simple nodes
are depicted as ovals and represent primitive values. The transaction time of nodes
and edges is represented by means of an interval. In this work, the authors define the
set of constraints needed to manage in a correct way the transaction time dimension,
and moreover describe the operations used to modify a GEM graph.
The GEM data model is general enough to represent both transaction and valid
times.
In Figure 1, a GEM graph managing valid time is represented. In this example
information about a group of restaurants is represented. The group of restaurants
is represented as a complex node having label composed by the name Group and
the valid time interval [01/05/05,now]. The name of the group (???Red Horse???) is
represented by means of a simple node related to the complex node Group.
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