is prohibited.
the time at which the system acquired this version, thus this proposal considers the
transaction time dimension. The model introduced in Marian et al. (2001) is based
on ordered trees, where all nodes have identifiers. The XML tree can be modified
by means of basic operations such as delete, insert, move, and update, after the
checking of consistency conditions.
In Wang and Zaniolo (2003), the authors propose XML-based techniques for managing
a multiversion document as a unit, and representing successive versions by
means of delta changes. In the XML document containing the successive versions
of a document, each element has two attributes, vstart and vend, which represent the
valid version interval of the element. The former attribute represents the moment
at which the element is first added to the XML document (i.e., the initial version
in which the element is valid), while the latter represents the moment at which the
element is removed from the XML document (i.e., the last version in which the element
is valid). The valid version interval can be represented by means of version
numbers or timestamps. In the case of timestamps, the considered time dimension
is the valid time.
To manage in a correct way the valid time dimension, the authors impose that the
version interval of an ancestor node always contains those of its descendant nodes.
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