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Main concepts of an extended ER model that offers IS-A constructs.
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Generalization/specialization hierarchies (IS-A relations for short) are basic semantic constructs proposed in most information system conceptual models. At the other side of design methodologies, where standard DBMSs are used, and will still be used for several years, there is no explicit representation of these IS-A relations. As a consequence, a...
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Context 1
... conceptual, logical and physical design, schema optimization, normalization and integration, database reverse engineering, system migration, conversion, maintenance and evolution. This model has been described in several recent papers [11,12,13,14], so that we can limit its presentation to mentioning the constructs that will be used in this paper (Fig. 3). A conceptual schema comprises mainly entity types, entity type attributes and relationship types. A collection of one or more entity types can be declared the subtypes of one or several entity types. An entity type can have one primary identifier (noted id, and generally underlined), and any number of secondary (or alternate) ...
Context 2
... downward inheritance, that represents the subtypes only ( Fig. 6.3); entity type A collects the entities that do not belong to subtypes B or C, if any. In techniques (1) and (2), some authors include a type attribute (with domain {'B','C'}) in the new version of A, in order to indicate to which subtype(s) each A entity belongs. We have omitted such an attribute in this discussion since it would be ...
Context 3
... is no problem to express these constraints into check or trigger clauses that are proposed by most current RDBMS. Fig. 23 and 24 illustrate the expression of simple and complex coexistence and exclusive constraints. At-least-one constraints will be translated in a similar way. Exactly-one constraints are formed by exclusive + at-least-one ...
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The widespread use of XML brings out the need of ensuring the validity of XML data. The use of languages such as XML Schema
makes easier the process of verification of XML documents, but the problem is that there are many constraints that can not
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in order to save XML designers from dealing with low level implementation issues. The approach of this paper is based on the
inclusion of such a conceptual level, using UML as a conceptual modeling language. Starting from a UML class diagram annotated
with conceptual constraints, our framework automatically generates an XML Schema together with a set of XSLT stylesheets to
check those integrity constraints that can not be expressed in XML Schema.
“Is_A” links are the core component of all ontologies and are organized into “hierarchies of concepts”. In this paper we will first address the problem of an automatic help to build sound hierarchies. Dependencies called “existence constraints” are the foundation for the definition of a “normalized” hierarchy of concepts. In the first part of the paper algorithms are provided to obtain a normalized hierarchy starting either from concepts or from instances using Boolean functions. The second part of the paper is devoted to the hierarchy maintenance: automatically inserting, merging or removing pieces of knowledge. We also provide a way to give synthetic views of the hierarchy.
One of the most severe problems related to database evolution is how to reflect in the data level the changes that have occurred
in the conceptual schema of a database. This is specially relevant when evolution operations affect ISA relationships. In
this paper we present our view of the evolution of ISA relationships, focusing on the artifacts that generate the sentences
for changing the data in a consistent way.
This paper analyzes the relationships between taxonomic constraints and derivation rules. The objectives are to see which
taxonomic constraints are entailed by derivation rules and to analyze how taxonomic constraints can be satisfied in presence
of derived types. We classify derived entity types into several classes. The classification reveals the taxonomic constraints
entailed in each case. These constraints must be base constraints (defined in the taxonomy) or be derivable from them. We
show how the base taxonomic constraints can be satisfied, either by the derivation rules (or the whole schema), or by enforcement.
Our results are general and could be incorporated into many conceptual modeling environments and tools. The expected benefits
are an improvement in the verification of the consistency between taxonomic constraints and derivation rules, and a guide
for the determination of the taxonomic constraints that must be enforced in the final system.
