Hierarchy - Query - 1 Table, 2 Levels
In some cases, a table for a lower-level entity also contains additional information for a higher-level entity. This often happens when no dedicated columns exist for the higher-level entity and the database designer decides that fully applying Third Normal Form (3NF) would involve more work than it seems to be worth, or they wish to optimize lookup speed. Although we strongly recommend using 3NF wherever possible, this tutorial demonstrates how to handle a scenario in which two levels share the same table.
In this example, besides storing the town ID and town NAME, our table also includes information about the COUNTRY in a separate column.
Database Schema
The cube defined in this example is based on two tables. Fact and Town. The Fact table contains a measures and a reference to the Town table. The Fact table is linked with its ID column to the Town table by the TOWN_ID column. The Town table has the ID, NAME and COUNTRY.
<roma:DatabaseSchema id="_dbschema">
<tables xsi:type="roma:PhysicalTable" id="_tab_fact" name="Fact">
<columns xsi:type="roma:PhysicalColumn" id="_col_fact_townId" name="TOWN_ID" type="Integer"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_fact_value" name="VALUE" type="Integer"/>
</tables>
<tables xsi:type="roma:PhysicalTable" id="_tab_town" name="Town">
<columns xsi:type="roma:PhysicalColumn" id="_col_town_id" name="ID" type="Integer"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_town_name" name="NAME"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_country" name="COUNTRY"/>
</tables>
</roma:DatabaseSchema>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Query Level
The TableQuery for the Level, as it directly references the physical table Town.
<roma:TableQuery id="_Query_LevelTown" table="_tab_town"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Query Fact
The TableQuery for the Level, as it directly references the physical table Fact.
<roma:TableQuery id="_query_Fact" table="_tab_fact"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Level
The level of the Town used the column attribute to define the primary key column and the nameColumn attribute.
<roma:Level id="_level_town" name="Town" column="_col_town_id" nameColumn="_col_town_name"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Level
The level of the Country used the column attribute to define the primary key column on the Country table of the Town table.
<roma:Level id="_level_country" name="Country" column="_col_country"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Hierarchy
This Hierarchy contains both defined levels. The primaryKey attribute defines the column that contains the primary key of the hierarchy. The query attribute references to the query that will be used to retrieve the data for the hierarchy.
The order of the Levels in the hierarchy is important, as it determines the drill-down path for the hierarchy.
<roma:Hierarchy id="_hierarchy_town" name="TownHierarchy" levels="_level_country _level_town" primaryKey="_col_town_id" query="_Query_LevelTown"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Dimension
The Dimension has only one hierarchy.
<roma:StandardDimension id="_dim_town" name="Town" hierarchies="_hierarchy_town"/>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Cube and DimensionConnector and Measure
The cube contains only one Measure in a unnamed MeasureGroup and references to the Dimension.
To connect the dimension to the cube, a DimensionConnector is used. The dimension has set the attribute foreignKey to define the column that contains the foreign key of the dimension in the fact table.
<roma:PhysicalCube id="_cube" name="Cube Query linked Tables" query="_query_Fact">
<dimensionConnectors foreignKey="roma:PhysicalColumn _col_fact_townId" dimension="roma:StandardDimension _dim_town"/>
<measureGroups>
<measures xsi:type="roma:SumMeasure" id="_measure" name="theMeasure" column="_col_fact_value"/>
</measureGroups>
</roma:PhysicalCube>Note: This is only a symbolic example. For the exact definition, see the Definition section.
Definition
This files represent the complete definition of the catalog.
<?xml version="1.0" encoding="UTF-8"?>
<xmi:XMI xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:roma="https://www.daanse.org/spec/org.eclipse.daanse.rolap.mapping">
<roma:Catalog name="Hierarchy - Query - 1 Table, 2 Levels" cubes="_cube" dbschemas="_dbschema"/>
<roma:DatabaseSchema id="_dbschema">
<tables xsi:type="roma:PhysicalTable" id="_tab_fact" name="Fact">
<columns xsi:type="roma:PhysicalColumn" id="_col_fact_townId" name="TOWN_ID" type="Integer"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_fact_value" name="VALUE" type="Integer"/>
</tables>
<tables xsi:type="roma:PhysicalTable" id="_tab_town" name="Town">
<columns xsi:type="roma:PhysicalColumn" id="_col_town_id" name="ID" type="Integer"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_town_name" name="NAME"/>
<columns xsi:type="roma:PhysicalColumn" id="_col_country" name="COUNTRY"/>
</tables>
</roma:DatabaseSchema>
<roma:TableQuery id="_Query_LevelTown" table="_tab_town"/>
<roma:TableQuery id="_query_Fact" table="_tab_fact"/>
<roma:Level id="_level_town" name="Town" column="_col_town_id" nameColumn="_col_town_name"/>
<roma:Level id="_level_country" name="Country" column="_col_country"/>
<roma:Hierarchy id="_hierarchy_town" name="TownHierarchy" levels="_level_country _level_town" primaryKey="_col_town_id" query="_Query_LevelTown"/>
<roma:StandardDimension id="_dim_town" name="Town" hierarchies="_hierarchy_town"/>
<roma:PhysicalCube id="_cube" name="Cube Query linked Tables" query="_query_Fact">
<dimensionConnectors foreignKey="_col_fact_townId" dimension="_dim_town"/>
<measureGroups>
<measures xsi:type="roma:SumMeasure" id="_measure" name="theMeasure" column="_col_fact_value"/>
</measureGroups>
</roma:PhysicalCube>
</xmi:XMI>Turorial Zip
This files contaisn the data-tables as csv and the mapping as xmi file.