Created: 2011-07-08 16:24
Updated: 2017-05-23 01:58

NCS Navigator MDES Module

This gem provides a consistent computable interface to the National Children's Study Master Data Element Specification. Most of the data it exposes is derived at runtime from the documents provided by the National Children's Study Program Office, which are embedded in the distribution package. The balance of the data is also derived from NCS PO documentation, but is preprocessed to reduce the footprint of this library.


require 'ncs_navigator/mdes'
require 'pp'

mdes = NcsNavigator::Mdes('3.0')
pp mdes.transmission_tables.collect(&:name)

For more details see the API documentation, starting with {NcsNavigator::Mdes::Specification}. (If you're not looking at this document in the API documentation, try looking at

As of ncs_mdes 0.12.1, Ruby 1.9.3+ and JRuby 1.7+ are supported. (Ruby 1.8.x is not supported as of 0.12.0. Use 0.11.0 or earlier for Ruby 1.8.7.)


This gem includes a console for interactively analyzing and randomly poking at the MDES. It is called mdes-console:

$ mdes-console
Documents are expected to be in the default location.
$mdesNM is a Specification for N.M.
Available specifications are $mdes12, $mdes20, $mdes21, $mdes22, and $mdes30.
:001 >

It is based on ruby's IRB. Use it to examine the loaded MDES data without a lot of edit-save-run cycles:

:001 > $
 => "study_center"

E.g., find all the variables of a particular XML schema type:

:002 > $mdes20.transmission_tables.collect { |t| t.variables } { |v| v.type.base_type == :decimal }.collect(&:name)
  => ["correction_factor_temp", "current_temp", "maximum_temp", "minimum_temp", "precision_term_temp", "trh_temp", "salts_moist", "s_33rh_reading", "s_75rh_reading", "s_33rh_reading_calib", "s_75rh_reading_calib", "precision_term_temp", "rf_temp", "correction_factor_temp", "sample_receipt_temp"]

Or the labels for a particular code list:

:003 > $mdes20.types.find { |t| == 'confirm_type_cl7' }.code_list.collect(&:label)
 => ["Yes", "No", "Refused", "Don't Know", "Legitimate Skip", "Missing in Error"]

Or the number of code lists that include "Yes" as an option:

:004 > $ { |t| t.code_list && t.code_list.collect(&:label).include?('Yes') }.size
 => 23

Or which variables in a table are different between two versions:

:005 > pp $mdes20['staff'].diff($mdes32['staff'])[:variables]; nil
 @right_only=["ncs_active_date", "ncs_inactive_date"]>


Writing API docs

Run bundle exec yard server --reload to get a dynamically-refreshing view of the API docs on localhost:8808.

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