== i2b2 Ontology and CRC Discussion: 1 ==
Questions asked and points to ponder. Access to the demo database is useful here...

=== Ontology Cell tables compared to CRC concept_dimension table ===
There are three ontology tables within the demo Ontology cell: birn, i2b2 and custom_meta.[[br]] 

When I do a select count(*) from <table_name> where c_visualattributes like '%LA%' I get the following figures:
   * birn: 37
   * custom_meta: 0
   * i2b2: 93807

When I do a "select count(*) from concept_dimension" within the CRC cell I get a count of 73590.[[br]]

The totals are 93844 as opposed to 73590. Why is there a difference and what does it mean?

=== In an Ontology table, what does c_columndatatype really mean? ===
The docs state: "either ‘T’ for text or ‘N’ for numeric and describes the datatype of the concept". Yet the length of the column is varchar 50.[[br]]

Within the demo project: 
   * select count(*) from i2b2 where c_columndatatype like '%N%' ===> returns 0
   * select count(*) from i2b2 where c_columndatatype like '%T%' ===> returns 134762
   * select count(*) from i2b2 ===> returns 134762

Yet within the query tool (from the Workbench) I can select terms from a Labtest and constrain by value. This is undoubtedly possible because of the optional metadataxml column. But even so, what '''''does''''' c_columndatatype really mean?[[br]]

=== Facts constrained by enumerated concepts ===
Facts can be constrained by simply pointing at a concept row within the concept_dimension table with very little else alongside it. For example, a numeric value like AGE can be divided into an enumeration of concepts, say one for each age from 0 to 114, as is the demo system. Here is a selection based upon this:
 select * from observation_fact where concept_cd like 'DEM|AGE:50' ;