In this section, we describe the different approaches proposed in the literature to
represent time in the semistructured data context (Chawathe et al., 1998; Combi et
al., 2004; Dyreson, B?¶hlen, & Jensen, 1999; Oliboni et al., 2001; Amagasa, Yoshikawa
& Uemura, 2001).
In Chawathe et al. (1998), the authors propose the delta object exchange model
(DOEM), a model based on the object exchange model (OEM) (Papakonstantinou
et al., 1995). Change operations (i.e., node insertion, update of node values, addition
and removal of labeled edges) are represented in DOEM by using annotations on
the nodes and edges of an OEM graph. Intuitively, annotations are the representation
of the history of nodes and edges. To implement the DOEM model the authors
use a method that encodes DOEM databases as OEM databases. This proposal
takes into account the transaction time dimension of a graph-based representation
of semistructured data. As OEM graphs, DOEM graphs do not consider labeled
relationships between two objects.
In Oliboni et al. (2001), the authors propose the temporal graphical model (TGM),
which is a graphical model for representing semistructured data dynamics. A TGM
graph is a directed labeled graph composed by two kinds of nodes (complex and
simple nodes), and two kinds of edges (relational and temporal edges). Complex
nodes are related to other complex nodes, and have a number of attributes (atomic
nodes), whereas atomic nodes represent objects with an atomic value (i.
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