C. Eick, "A Methodology for the Design and Transformation of Conceptual Schemas", in 17th Conference on VLDB, Ed. pp. 25 - 34, 1991.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....in the range of = For a subset of the universe, Y U , I Y (S) denotes the set of instances of S that contain only symbols in Y . 4 Information Capacity We consider formal notions of correctness for schema transformations that are based on the preservation of the information content of schemas[3, 4, 7, 9]. For a schema S, the latter is the set of valid instances, I(S) Intuitively, a schema S2 has more information capacity than a schema S1 if every instance of S1 can be mapped to an instance of S2 without loss of information. Specifically, it must be possible to recover the original instance from ....

....similar results, the question remains as to how practitioners can develop rigorous methodologies. Our response is to propose sets of schema transformations on SIGs that preserve or augment information capacity and are similar to transformations in existing integration and translation methodologies [3, 6, 7, 9]. For each set of transformations, we characterize precisely when a schema can be created from another through any arbitrary sequence of transformations. Our characterizations are couched in terms of definitions of dominance and equivalence having the following properties: 1 each is a sufficient ....

C. F. Eick. A Methodology for the Design and Transformation of Conceptual Schemas. In Proc. of the Int'l Conf. on Very Large Data Bases, pages 25--34, Barcelona, Spain, Sept. 1991.

....sequence of ff transformations or ffi transformations. Corollary 5.5 If S1 ffffi Gamma S2 then S1 int S2. ffl Several researchers have made use of information or equivalence preserving transformations that move or copy attributes between entities or classes within other data models [7, 17]. These transformations are special cases of ffi transformations. However, no complete characterization of dominance under these transformations has been given. Hence, it was not previously possible to determine if an arbitrary schema could be transformed into another via these transformations. ....

C. F. Eick. A Methodology for the Design and Transformation of Conceptual Schemas. In Proc. of the Int'l Conf. on Very Large Data Bases, pp. 25--34, Barcelona, Spain, Sep. 1991.

.... many intuitive information preserving mappings from I(S1) to I(S2) where each instance of emp1 is mapped to some instance of emp2 with the same employees (i.e. the same eno, 1 Information capacity has been used extensively in the translation and integration literature [AABM82, BC86, Bor78, Eic91, Hul86, HY84, MS92, Ris82, RR87, and others] While the precise details of the definitions differ among authors, we present definitions that are in keeping with the spirit of the existing literature. but also the same ename and sal) ignoring the values of age. Therefore, S2 dominates S1 (S1 ....

....importance of verifying the correctness of a transformation. 7 We use an intuitive QUEL like query language to illustrate query modification. 5.1. 7 Related Work Other methodologies describe related transformations by example or provide mechanisms for defining views with similar effects [DH84, Eic91] Similar assumptions are typically required to ensure these transformations create equivalent schemas. This same example can also be modified to show that the information ordering used in other schema merging proposals does not correspond to information capacity dominance [BDK92] 5.2 Merging ....

C. F. Eick. A Methodology for the Design and Transformation of Conceptual Schemas. In Proc. of Conf. on VLDB, pages 25--34, Barcelona, Spain, 1991.

....may be implicit constraints on the source database which are not included in the source schema, either because they are not expressible in the data model being used or simply because they were forgotten or not anticipated at the time of initial schema design. An alternative approach, pursued in [11], is to attempt to define information preserving transformations and valid schemas with respect to some underlying universe of discourse . However such characterizations are impossible or impractical to represent and verify in practice. 4.2 Information Capacity and Constraints In [23,24] Miller ....

C. Eick. A methodology for the design and transformation of conceptual schemas. In Proceedings of the 17th International Conference on Very Large Databases, Barcelona, Spain, pages 25--34, September 1991.

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C. Eick, "A Methodology for the Design and Transformation of Conceptual Schemas", in 17th Conference on VLDB, Ed. pp. 25 - 34, 1991.

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