Refine exposure database schema

[Vitor Silva]

The openquake database and NRML schema need to be extended to support the following optional parameters:
 - flag to stablish the distinction between single and grouped asset;
 - limit, deductible, content value, economy variable (TBD) : double value;
 - occupancy type : string;
 - occupants, time element : integer value.

[Lars Butler (lars-butler)]

More details needed:
- Are there prototypes for the new NRML content?
- What is the difference between a 'single' and a 'grouped' asset?
  - Do we need to create the concept of an 'asset group' as some sort of container?
- How does this affect OpenQuake's treatment of assets defined in the exposure model?

[Vitor Silva (vitor-silva)]

Currently in order to define an asset the following parameters need to be defined:
 location: pair of coordinates (latitude,longitude)
  - value: number of buildings, economic value, built up area.
  - taxonomy: building typology, used to relate with a vulnerability function.

This configuration does not allow users to store the information mentioned in the attribute "Value" simultaneously, which means, only one parameter about the quantity of the asset can be stored in the exposure model. In order to fix this issue, the nrml schema/database should be extended to included the following list of parameters per asset:
 - location;
 - number;
 - structuralCost;
 - area;
 - taxonomy;

The current schema supports an attribute named "units" that establishes how the Value of the Asset is being measured (e.g.: EUR, USD). With the inclusion of the new parameters, two attributes of this type should be supports:
 - structuralCostUnits: currency used to quantify the economic value
 - areaUnits: measure used to quantify the built up area.

The two aforementioned parameters (structuralCost and area) can vary significantly, according to how the information about the exposed elements were gathered and/or processed. For instance, the structuralCost of an asset can be quantified as the value of a single element (e.g.: replacement cost of a single RC building), value per unit of area (e.g: replacement cost per square meter) or aggregated value (sum of the economic value of all the buildings assumed to exist at a given location). The attribute area also varies in a similar manner. It could represent the built up area of a single asset, or the aggregated built up area of all the elements. Thus, two flags should be included in the exposure model clarifying what type of information is being provided by these parameter:
 - structuralCost: 1 – per_asset; 2 – per_area; 3 – aggregated.
 - area: 1 – per_asset; 2 – aggregated.

Such modifications in the exposure model will also cause a set of changes in the OpenQuake calculator. For the Scenario Risk, Probabilistic Event-based Risk, Classical PSHA-based Risk and Retrofitting Benefit Cost Ratio calculators, the economic value of each asset is required. This parameter might not be provided directly by the exposure model but can be calculated relating the tree parameters. The following cases may occur:
 - structuralCost = aggregated economic value: This case is what happens currently. In order to compute the final losses, OQ simply multiplies the final loss ratio for this value. No need to make use of the other parameters.
 - structuralCost = replacement cost per area; area = aggregated area: In this case, the economic value will be equal to structuralCost x area.
 - structuralCost = replacement cost per asset: For this case the economic value will be equal to structuralCost x number.
 - structuralCost = replacement cost per area; area = area of single asset; The tree parameters need to be used and the economic value will be equal to structuralCost x area x number.

Such modifications will also allow to increase the reliability of the calculators by using a different approach to sample the residuals of the loss ratios and ...

[Muharem Hrnjadovic (al-maisan)]

Related bug #922134.

[Muharem Hrnjadovic (al-maisan)]

An example of the new exposure NRML: http://pastebin.com/d6g3ZSvE

[Muharem Hrnjadovic (al-maisan)]

New exposure model with abbreviations: http://pastebin.com/DfD5BeRm

[Vitor Silva (vitor-silva)]

The abbreviations proposed in #5 are definetely a good idea as they will cause a significant decrease in the exposure model files size.

[Muharem Hrnjadovic (al-maisan)]

This bug will be used to track the database changes only.

[Muharem Hrnjadovic (al-maisan)]

The NRML work is tracked via bug #927517

[Muharem Hrnjadovic (al-maisan)]

Calculation of the per-assset economic value is tracked via bug #927525

[Muharem Hrnjadovic (al-maisan)]

https://github.com/gem/openquake/pull/679