In this article we brie(cid:3)y present the idea of de(cid:2)ning a kernel for object role modelling techniques, upon which different drawing styles can be based. We propose such a kernel (the ORM kernel) and de(cid:2)ne, as a case study, an ER and a NIAM drawing style on top of it. One of the prominent advantages of such a kernel is the possibility to build a CASE-tool supporting multiple methods. Such a CASE-tool would allow users with different methodological backgrounds to use it and view the modelled domains in terms of their favourite method. This is illustrated using a running example of a concrete domain in which we use the ORM kernel in combination with the NIAM and ER drawing style.
The focus of this paper is database design in the context of converting a conceptual data model into an internal representation. For a given conceptual data model, an access pro-le speciies statistical information about (retrieval and update) requests to be performed, while a data proole speciies a statistical characterization of the database contents. The corresponding time/space trade-oo and update/retrieval trade-oo are usually very untrans-parent, especially in the case of large databases with many diierent fact types, combined with complex prooles. In this paper we describe a general strategy for examining the trade-oos for a given application, and for constructing and trying-out several (diierent) databases for the same conceptual data model (multiprototyping).
The design of relational databases tipically starts with the definition of a conceptual schema which describes the conceptual structures of the database in terms of a high-level data model, such as the ER and NIAM models, and then proceeds by mapping this conceptual schema into a relational representation. However, this mapping has been usually described in terms of a basic “cannonical” relational model, which means that most of the integrity constraints specified at the conceptual level are not fully captured in the final relational reperesentation. The recent SQL standard proposal has provided a new framework for discussing the design of relational databases, since it introduces a number of facilities which capture most of the integrity constraints specified in a conceptual schema. In this paper, we discuss the general aspects involved in the mapping of NIAM schemas into SQL. We present a mapping procedure which handles the basic NIAM constructs and then discuss how to extend it to cope with the more complex ones. We also address the problem of optimizing the SQL representation of NIAM schemas to reduce the number of referential constraint definitions in the final SQL representation. We point out that, besides reducing the number of referential constraint definitions, the mapping strategy applied also simplifies the mapping of NIAM inter-relationship constraints.
