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of these works assume that conflict resolution will be fully automatic. Additionally,
most of these works assume that there is no
structural
conflict (e.g., that a merged
column should belong to two different tables). This kind of more complex conflict
resolution is explored more fully in the next section.
3.3
Spaccapietra and Parent
Spaccapietra and Parent
[
1994
] work in the context of ERC
[
Spaccapietra et al.
1992
], which extends an early version of entity relationship diagrams [
Chen 1976
].
In ERC
C
, there are three basic types of objects: attributes, entities, and relation-
ships. While there are differences between ERC
C
and Chen's original ER diagram,
for the purposes of this paper, the primary difference is that ERC
C
C
allows complex
attributes (i.e., attributes can have subattributes) (Fig.
8.1
).
Spaccapietra and Parent assume that the matching or aligning work has already
been completed by the database administrator or some view integration tool. Their
method for merging the data once these mappings (based on Superviews [
Motro
1987
]) have been created is fully automatic. However, this is at least partially pos-
sible because the authors do not consider constraints or ordering of any type, thus
avoiding the undecidability result of Sect.
2.2
.
Spaccapietra and Parent
[
1994
] concentrates on rules for view integration, and
the merging algorithm that uses them. They have two overriding principles: (1) inte-
gration rules should apply to both objects and the links between them, and (2) if
there is a choice to be made, they choose the least restrictive option. According to
these principles, they have created 6 integration rules that can be combined for their
merging algorithm. The rules, as named by Spaccapietra and Parent, are:
1.
Elements integration rule:
For any two matching elements that are not of the
same type, the resulting element is an entity type. If the two matching types are
Student
Enrolled
Class
Name
Ugrad
Grad
SAT Score
Office
Verbal
Math
Fig. 8.1
diagram. The entities are represented by
rectangles
, the relationships
are represented by
diamonds
, and attributes are represented by plain text
An example ERC
C
