Observation_Period-Mapping.md

+# Observation_Period Mapping
+
+:information_source: This table records the very first visit and very last visit of a patient. The information is retrieved from Encounter resources.
+
+## Encounter to OBSERVATION_PERIOD
+| Source | Target | Comments |
+| :---------------- | :---------------------- | :------------------------------------------------- |
+||observation_period_id|this id is automatic generated in database|
+|subject.reference|person_id|the `person_id` from PERSON|
+|recordedDate <br>onsetPeriod.start <br> onsetDateTimeType|observation_period_start_date <br> observation_period_end_date|the very first visit <br> the very last visit |
+||period_type_concept_id|44818701 (Period covering healthcare encounters)|
+
+## Example
+|observation_period_id|person_id|observation_period_start_date|observation_period_end_date|period_type_concept_id|
+|-----|-----|-----|-----|-----|
+|1|1|2018-09-17|2018-09-26|44818701|
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