Unit 5: Use Case #2 – One-to-Many Mapping

In this unit, we'll take a closer look at a second use case involving one-to-many mapping.

One-to-many mapping explained

In our second use case of transcoding data, we focus on a one-to-many mapping challenge along with possible solutions and a moment to reflect on each approach.

Select each option below to explore the details.

Challenge
Source dataset
The source dataset has the dimensions with ID "FREQ", "REF_AREA", and "INDICATOR".

Indicator dimension
The INDICATOR dimension uniquely defines a series (Example: INDICATOR1, INDICATOR2, INDICATOR3).

Target DSD
The Target DSD has FREQ and REF_AREA but splits INDICATOR into multiple dimensions: SEX, EDUCATION_LEVEL, STATISTICAL_UNIT.

Mapping rules
The mapping rules split the unique key:

  • INDICATOR1 maps to FREQ:A, REF_AREA:UK, SEX:_T, EDU_LEVEL=PRIMARY, STAT_UNIT=ENROLMENT
  • INDICATOR2 maps to FREQ:A, REF_AREA:UK, SEX:F, EDU_LEVEL=PRIMARY, STAT_UNIT=ENROLMENT
  • INDICATOR3 maps to FREQ:A, REF_AREA:UK, SEX:M, EDU_LEVEL=PRIMARY, STAT_UNIT=ENROLMENT
Solution A
This type of use case can be solved by creating three component maps:
  • Component map 1: Source=INDICATOR Target=SEX
  • Component map 2: Source=INDICATOR Target=EDU_LEVEL
  • Component map 3: Source=INDICATOR Target=STAT_UNIT

Each component map is backed by a representation map, which maps the value of the Unique Key to the output as follows:

Select the representation map to enlarge.

Solution B
An alternative solution is to create a single component map, which maps the source INDICATOR to three outputs: SEX, EDU_LEVEL, STAT_UNIT.

A single representation map is required to map each INDICATOR to the three outputs.

INDICATOR -> SEX:EDU_LEVEL:STAT_UNIT

Values:

  • INDICATOR1=_T:PRIMARY:ENROLMENT
  • INDICATOR2=F:PRIMARY:ENROLMENT
  • INDICATOR3=M:PRIMARY:ENROLMENT
Reflection
The choice of whether to split the mapping up into separate components (Solution A) versus a single rule (Solution B), should be based on what will be more maintainable and understandable, along with whether individual mapping rules will be reused by other structure maps or not.

One-to-many mapping in action

Now let's take a look at an example of one-to-many mapping in action. In this short video, we'll examine creating the structures in FMR and then transcoding the datafiles using the API – sync & async.

Select Play to begin.

To access the code presented in this video, click here.

Coming next

In the next unit, we'll go over the third use case scenario involving many-to-one mapping.

Unit 4: Use Case #1 – One-to-One Mapping
Unit 6: Use Case #3 – Many-to-One Mapping
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