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Like many these days, I am an old relational-model user approaching Cassandra for the first time. I have been trying to understand Cassandra's data model, and when I read about it I frequently encounter statements that encourage me to think about it as 4 and 5 dimensional maps.
Now I'm familiar with an ordinary key/value Map, but I have never thought of how many dimensions it has, and that gives me no basis to plunge headlong into trying to visualize 4 and 5 dimensions.
Is there a more gentle introduction to dimensionality in maps? How many dimensions are there in an ordinary hashtable? One? Two? Zero?
If an ordinary hashtable has, say, just one dimension, then what would a two-dimensional map be? If two, then what would a 3-dimensional map be?
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Dimensions are a special kind of geodatabase annotation for showing specific lengths or distances on a map. A dimension may indicate the length of a side of a building or land parcel or the distance between two features such as a fire hydrant and the corner of a building.
Multi-dimension mapping enables you to define member mapping based on multiple source column values. This functionality provides you with the ability to load data into dimensions unavailable in the target application.
A map is a 2-dimensional sketch Acquiring only two dimensions, such as width and height but no density or thickness. Sq., Circles, Triangles, etc. are two-dimensional subjects and are Also known as "2D".
Having only two dimensions, such as width and height but no thickness. Squares, Circles, Triangles, etc are two-dimensional objects. Also known as "2D".
Map<String, String> -- One dimension
Map<String, Map<String, String>> -- Two dimensions
Map<String, Map<String, Map<String,String>>> -- Three dimensions
etc...
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Encouraging you to think of it as 4 or 5 dimensional maps is one of the best signs that the author of what you're reading doesn't know what he's talking about.
Read the Max Grinev posts linked at the top of http://wiki.apache.org/cassandra/ArticlesAndPresentations instead.
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