Implementing Operations to Navigate Semantic Star Schemas

In the last years, lots of work have been devoted to multidimensional modeling, star shape schemas and OLAP operations. However, “drill-across ” has not captured as much attention as other operations. This operation allows to change the subject of analysis keeping the same analysis space we were using to analyze another subject. It is assumed that this can be done if both subjects share exactly the same analysis dimensions. In this paper, besides the implementation of an algebraic set of operations on a RDBMS, we are going to show when and how we can change the subject of analysis in the presence of semantic relationships, even if the analysis dimensions do not exactly coincide

Definition of Derived Classes in OODBs

According to the ANSI/SPARC architecture, external schemas are derived from the database conceptual schema. In object-oriented databases (OODBs), an external schema may include classes defined in the conceptual schema just as it may also contain derived classes which are directly or indirectly defined on the basis of conceptual schema classes. In the definition of derived classes in OODBs three main issues have to be resolved, namely: the integration of derived classes with other classes in an object schema; the definition of classes with new objects; and the transmission of modifications between the objects in derived classes and those of the classes from which they are defined. A solution to the first issue was proposed in [18] and [19]. In this paper, the two remaining issues are further studied and new conceptual level solutions are put forward. Our proposals are informally illustrated through some examples.

Multi-star Conceptual Schemas for OLAP

OLAP tools divide concepts based on whether they are used as analysis dimensions, or are the fact subject of analysis, which gives rise to star shape schemas. Operations are always provided to navigate inside such star schemas. However, the navigation among different stars use to be forgotten. This paper studies different kinds of conceptual relationships between stars (i.e. Derivability, Generalization/Specialization, Aggregation /Decomposition, or Temporal), and proposes a 3-level schemas architecture to ease the implementation and usage of multi-star schemas

External Schema Generation Algorithms for Object Oriented Databases

ABSTRACT. In this paper two external schema generation algorithms are presented. These algorithms are defined in the framework of the new external schema definition methodology for OODBs put forward in (Samos, 1995); they generate an external schema from a set of classes selected from those existing in an external schema definition repository. Their main characteristic is that they avoid the generation of auxiliary classes that are not included in the defined external schema. KEY WORDS: OODB, views, external schemas, class integration. 1