Dimensional modeling | EPFL Graph Search

Dimensional modeling (DM) is part of the Business Dimensional Lifecycle methodology developed by Ralph Kimball which includes a set of methods, techniques and concepts for use in data warehouse design. The approach focuses on identifying the key business processes within a business and modelling and implementing these first before adding additional business processes, as a bottom-up approach. An alternative approach from Inmon advocates a top down design of the model of all the enterprise data using tools such as entity-relationship modeling (ER). Description Dimensional modeling always uses the concepts of facts (measures), and dimensions (context). Facts are typically (but not always) numeric values that can be aggregated, and dimensions are groups of hierarchies and descriptors that define the facts. For example, sales amount is a fact; timestamp, product, register#, store#, etc. are elements of dimensions. Dimensional models

Isogeometric Analysis for an earthquake simulation

Christoph Jäggli

We consider Isogeometric Analysis to simulate an earthquake in a two dimensional model of a sinusoidal shaped valley. We analyze two different time integration schemes, namely the Generalized- and the Leap-Frog methods. Solving a wave propagation problem leads to a numerical dispersion of the wave velocities which depends on the discrete function space, as well as on the direction of propagation. In this work we also analyze the numerical dispersion with respect to the number of quadrature nodes per wavelength and the direction of wave propagation.

2013

Ensemble modelling of ice cover for a reservoir affected by pumped-storage operation and climate change

Ulrike Kobler, Martin Schmid

Ensemble modelling was used to assess the robustness of projected impacts of pumped-storage (PS) operation and climate change on reservoir ice cover. To this end, three one-dimensional and a two-dimensional laterally averaged hydrodynamic model were set up. For the latter, the strength of the impacts with increasing distance from the dam was also investigated. Climate change effects were simulated by forcing the models with 150 years of synthetic meteorological time series created with a weather generator based on available air temperature scenarios for Switzerland. Future climate by the end of the 21(st) century was projected to shorten the ice-covered period by similar to 2 months and decrease ice thicknesses by similar to 13 cm. Under current climate conditions, the ice cover would already be affected by extended PS operation. For example, the average probability of ice coverage on a specific day was projected to decrease by similar to 13% for current climate and could further be reduced from similar to 45% to similar to 10% for future climate. Overall, the results of all models were consistent. Although the number of winters without ice cover was projected to increase for all one-dimensional models, studying individual segments of the two-dimensional model showed that the impact was pronounced for segments close to the PS intake/outlet. In summary, the reservoir's ice cover is expected to partially vanish with higher probability of open water conditions closer to the PS intake/outlet.

WILEY2019

Conceptual modeling of multimedia databases

Oleksandr Drutskyy

The gap between the semantic content of multimedia data and its underlying physical representation is one of the main problems in the modern multimedia research in general, and, in particular, in the field of multimedia database modeling. We believe that one of the principal reasons of this problem is the attempt to conceptually represent multimedia data in a way, which is similar to its low-level representation by applications dealing with encoding standards, feature-based multimedia analysis, etc. In our opinion, such conceptual representation of multimedia contributes to the semantic gap by separating the representation of multimedia information from the representation of the universe of discourse of an application, to which the multimedia information pertains. In this research work we address the problem of conceptual modeling of multimedia data in a way to deal with the above-mentioned limitations. First, we introduce two different paradigms of conceptual understanding of the essence of multimedia data, namely: multimedia as data and multimedia as metadata. The multimedia as data paradigm, which views multimedia data as the subject of modeling in its own right, is inherent to so-called multimedia-centric applications, where multimedia information itself represents the main part of the universe of discourse. The examples of such kind of applications are digital photo collections or digital movie archives. On the other hand, the multimedia as metadata paradigm, which is inherent to so-called multimedia-enhanced applications, views multimedia data as just another (optional) source of information about whatever universe of discourse that the application pertains to. An example of a multimedia-enhanced application is a human-resource database augmented with employee photos. Here the universe of discourse is the totality of company employees, while their photos simply represent an additional (possibly optional) kind of information describing the universe of discourse. The multimedia conceptual modeling approach that we present in this work allows addressing multimedia-centric applications, as well as, in particular, multimedia-enhanced applications. The model that we propose builds upon MADS (Modeling Application Data with Spatio-temporal features), which is a rich conceptual model defined in our laboratory, and which is, in particular, characterized by structural completeness, spatio-temporal modeling capabilities, and multirepresentation support. The proposed multimedia model is provided in the form of a new modeling dimension of MADS, whose orthogonality principle allows to integrate the new multimedia modeling dimension with already existing modeling features of MADS. The following multimedia modeling constructs are provided: multimedia datatypes, simple and complex representational constraints (relationships), a multimedia partitioning mechanism, and multimedia multirepresentation features. Following the description of our conceptual multimedia modeling approach based on MADS, we present the peculiarities of logical multimedia modeling and of conceptual-to-logical inter-layer transformations. We provide a set of mapping guidelines intended to help the schema designer in coming up with rich logical multimedia document representations of the application domain, which conform with the conceptual multimedia schema. The practical interest of our research is illustrated by a mock-up application, which has been developed to support the theoretical ideas described in this work. In particular, we show how the abstract conceptual set-based representations of multimedia data elements, as well as simple and complex multimedia representational relationships can be implemented using Oracle DBMS.

EPFL2009

Conceptual modeling of multimedia databases

Oleksandr Drutskyy

EPFL2009