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Benedikt Kämpgen http://b-kaempgen.de/index.php?title=RollupOp&diff=620&oldid=prev 2013-09-06T13:02:01Z

<p>‎<span dir="auto"><span class="autocomment">Relationship between level_number, hierarchy_max_level_number and levelHeight</span></span></p> <p><b>New page</b></p><div>This operator rolls up a Dimension of a Cube (the former LogicalOlapOp) to a specific higher Level. We assume a [[LEAN Data Cube]] (i.e., dataset with observations on the lowest levels only).<br /> <br /> SliceOp gets as input an input operator, a List&lt;Node[]&gt; list with a header and levels according to [[Olap4ld_Metadata#getLevels.28.29]] to rollup to.<br /> <br /> ==Problem: How to rollup in Linked Data?==<br /> * In ROLAP, the LEVEL_NUMBER of a level does not lead to more difficult queries, since we simply need to group by the specific level column of the dimension table<br /> * In OLAP4LD, the lower the level depth (the higher the level in the hierarchy), the longer the skos:narrower path.<br /> * A hierarchy in Linked Data is represented using a skos:narrower path starting from skos:hasTopConcept from the skos:ConceptScheme. In a [[LEAN Data Cube]], we only have observations on the lowest levels (the most detailed levels). How do we know which levels are the lowest levels?<br /> * Solutions<br /> ** We add a new property HIERARCHY_MAX_LEVEL_NUMBER to HIERARCHY saying the number of levels. This number we can retrieve by aggregating the number of skos:ClassificationLevels attached to the code list.<br /> ** We compute the skos:narrowerTransitive closure from all skos:Concepts and either take observations that are linked to each concept directly or linked to a concept that is linked via skos:narrowerTransitive to the concept.<br /> * We try solution 1.<br /> <br /> ==Relationship between level_number, hierarchy_max_level_number and levelHeight==<br /> [[File:Olap4ld_level_number_vs_levelHeight.png]]<br /> <br /> LevelHeight = MAX_LEVEL_NUMBER - LEVEL_NUMBER<br /> <br /> '''Note:''' root level number = 0, but root level is implicit (slice).<br /> <br /> ==Problem 3==<br /> <br /> ==Problem 4==</div>

Benedikt Kämpgen