also sprach martin f krafft <madduck@madduck.net> [2003.02.17.0930 +0100]:
> only looking for specific features that differ, but also (and more)
e.g.:
ORDER:
records are unordered in the relational model, but ordered in the
other two.
INHERENT CONSTRAINTS:
records cannot exist without a parent/relating record in the
hiearchical model due to the structure. the existence of unrelated
records in the relational and network model can be controlled by
the data-definition language and/or the design of the various
record types.
RELATIONSHIPS:
in the hierarchical model, a record must have one and only one
record from which it is deviated. in the network model, there can
also only be one parent record (but there doesn't have to be). in
the relational model, such constraints don't exist. (this all
means jack when working with "virtual parents")
CASCADING:
a deletion of a "parent" record automatically removes children in
the hierarchical model. the same *can* be true for the relational
and the network model (not sure about the latter), but it has to
be configured in the DDL, i.e. it's not inherent.
CURRENCY:
operations in the relational model always start from the "global"
position whereas there is a position pointer maintained in the
DBMS in the other two models. Operations in the hierarchical and
network models are mostly relative to that position pointer.
--
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.''`. martin f. krafft <madduck@debian.org>
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