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# Dimensional modelingowb11gr2 paper

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### Dimensional modelingowb11gr2 paper

1. 1. Dimensional Modelling with OWB 11gR2 Maren Eschermann Trivadis AG Zürich
3. 3. dimension wizard the specification of a dimension can be done in a few steps. Not only thedimension is created but also the dimension table and a sequence are created as OWB meta-objects. A dimension table has the following properties:  Table name = <DIMENSION NAME>_TAB  A primary key on the DIMENSION_KEY column  A number of columns for each level  An index on the business key of each level If dimension properties are modified, you have to perform an “automatic binding” to propagate these modifications to the underlying dimension table. If you have manually modified this table beforehand, all your modifications (comments, additional constraints, …) will be overwritten. Moreover the primary key of the dimen- sion table gets a new name, this results in an error if you already have fact tables referencing the dimension.If project specific guidelines exist, which are not compatible with automatic binding and theresulting dimension table properties, you can disable the auto binding feature and do the bindingbetween the dimension and its table manually. This way you have all freedom concerning thenaming, definition of constraints and other properties of the dimension table.A dimension object has properties which are only applicable if the dimension operator is used astarget operator in a mapping. This is true for configurations concerning historization (SlowlyChanging Dimension) and orphan management. In chapter 3.2 we will elaborate on that topic inmore detail.OWB 11.2 offers some advanced possibilities concerning the modeling of dimensions. In 11.2 itis possible to create a dimension without surrogate key, which allows having degeneratedimensions for example.2.3 Time DimensionEffectively each fact table references the time dimension at least once, very often the fact table ispartitioned by time. In earlier versions the time dimension table had a surrogate key like all otherdimension tables, which have been referenced by the fact tables. With this the partitioning bytime was difficult. OWB 11.2 realizes the time dimension table with a date column as primarykey. This way also the fact table has a date column and partitioning can be easily done.2.4 Modeling a CubeA cube consists of measures (facts), dimensionsand aggregation rules, which define how themeasures can be aggregated along thehierarchies of the dimensions.With the cube wizard the user can define acube and all its properties.info@trivadis.com . www.trivadis.com . Info-Tel. 0800 87 482 347 . Datum 11.01.2012 . Seite 3 / 8