José Samos

YAM 2 : a multidimensional conceptual model extending UML

This paper presents a multidimensional conceptual Object-Oriented model for Data Warehousing and OLAP tools, its structures, integrity constraints and query operations. It has been developed as an extension of UML core metaclasses to facilitate its usage, and try to fill the absence of a standard model. Being a UML extension allows reusing modeling constructs and techniques, and integrating multidimensional modeling in more general modeling processes. Moreover, while existing multidimensional models are restricted to the modeling of isolated stars, this paper investigates the representation of several semantically related star schemas. Summarizability and identification constraints can also be represented in the model, and a closed and complete set of algebraic operations has been defined in terms of functions (so that mathematical properties of functions can be smoothly applied).

YAM/sup 2/ (yet another multidimensional model): an extension of UML

This paper presents a multidimensional conceptual object-oriented model, its structures, integrity constraints and query operations. It has been developed as an extension of UML core metaclasses to facilitate its usage, as well as to avoid the introduction of completely new concepts. YAM/sup 2/ allows the representation of several semantically related star schemas, as well as summarizability and identification constraints.

A Framework for the Classification and Description of Multidimensional Data Models

The words On-Line Analytical Processing bring together a set of tools, that use multidimensional modeling in the management of information to improve the decision making process. Lately, a lot of work has been devoted to modeling the multidimensional space. The aim of this paper is two fold. On one hand, it compiles and classifies some of that work, with regard to the design phase they are used in. On the other hand, it allows to compare the different terminology used by each author, by placing all the terms in a common framework.

On relationships offering new drill-across possibilities

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 is usually overlooked. This paper studies different kinds of Object-Oriented conceptual relationships (part of UML standard) between stars (namely Derivation, Generalization, Association, and Flow) that allow to drill across them.

Building Secure Data Warehouse Schemas from Federated Information Systems

There are certain similarities between architectures for Federated Information Systems and architectures for Data Warehousing. In the context of an integrated architecture for both Federated Information Systems and Data Warehousing, we discuss how additional schema levels provide security, and operations to convert from one level to the next.

Benefits of an Object-Oriented Multidimensional Data Model

In this paper, we try to outline the goodness of using an O-O model on designing multidimensional Data Marts. We argue that multidimensional modeling is lacking in semantics, which can be obtained by using the O-O paradigm. Some benefits that could be obtained by doing this are classified in six O-O-Dimensions (i.e. Classification/Instantiation, Generalization/Specialization, Aggregation/De-composition, Behavioural, Derivability, and Dynamicity), and exemplified with specific cases.

External Schema Generation Algorithms for Object Oriented Databases

In this paper two external schema generaion algorithms are presented. These algorithms are defined in the framework of the new external schema definition methodology for OODBs pur 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.

Primitive Operations for Schema Evolution in ODMG Databases

Schema evolution is the process of applying changes to a schema in a consistent way and propagating these changes to the instances while the database is in operation. In this process there are two problems to consider: semantics of change and change propagation. In this paper, we study the problem of the semantics of change for the schema evolution defined with the ODMG object model. In this context, we provide a formal definition of this object model, we establish a set of axioms to ensure the consistency of a schema when it is modified, and we define a set of primitive operations that allow basic changes to be carried out on an ODMG schema. Other operations, which allow any kind of modification to be carried out, can be derived from these primitives.

Generation of external schemas in ODMG databases

A method for generating external schemas in object oriented databases in the ODMG framework is proposed. External schema generation involves obtaining all the relationships existing between the classes selected to make up an external schema. This generation process is part of an external schema definition system that we are developing, which allows the definition of external schemas in ODMG. External schemas generated with this process do not extend the object oriented paradigm, and the generation of unnecessary intermediate classes is avoided.

Definition of External Schemas in ODMG Databases

ODMG 3.0 (January 2000) does not specify how to define external schemas in object oriented databases and only offers a very basic mechanism for defining views, called named queries. In this paper, a system and a language for defining external schemas in ODMG databases are presented. Both are based on a mechanism that avoids the generation of classes that are not necessary in external schemas. The proposed language is an extension of ODMG ODL and allows the definition of external schemas using the ODMG named queries for defining derived classes. Nevertheless, the proposed language is independent of the derived classes definition mechanism used.