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Semantic Equivalence

The screen shot below shows a visual representation of the fact tables of two XBRL instances/XBRL taxonomies. 

The top fact table representation comes from the XBRL instance/XBRL taxonomy example in the business use case "Classes" and models the components of PPE as the [Member]s of an [Axis] (using US GAAP taxonomy lingo) or dimensions of one primary item (using XBRL Dimensions lingo).

The bottom fact table representation comes from the XBRL instance/XBRL taxonomy example in the business use cases "Simple Roll Up" and models the components of PPE as concepts within a set of [Line Items] (using US GAAP taxonomy lingo) or primary items (using XBRL Dimensions lingo).

Are the two facts which express the fact value of "Land" semantically equivalent?

You probably answered "YES".  That is the answer which I would have given.  While syntactically the two facts are modeled using different approaches; semantically they say the same thing. (If you don't agree that the answer is YES, I would enjoy hearing your rational.)

So, if they are semantically equivalent; can you just take the fact in line #1 on the top fact table out and replace it with #11 from the bottom fact table?  Of course you cannot because the modeling approach of the top fact table and the modeling approach of the bottom fact table are different.

Neither modeling approach is wrong.  However, approaches must not be arbitrarily mixed.

Yet this is a common mistake in modeling SEC XBRL financial filings which I have seen.  One of the areas where this appears the most is the modeling of classes of preferred and common stock.  Mixing these approaches causes things like balance sheets which do not balance.

Something which this brings up is how do you know whichmodeling approach to use? That is a good question.  Sometimes you don't really have a choice because if you are either extending an existing model or fitting another piece into some other model you need to fit your modeling into that existing model.  Other times there is no clear answer.  For example, in the US GAAP taxonomy sometimes both approaches are modeled and it can be confusing which to use if there are no other constraints to consider.

Posted on Friday, November 2, 2012 at 08:46AM by Registered CommenterCharlie in | CommentsPost a Comment

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