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When the person table was initially introduced into OpenMRS, all implementations were constrained to use the same attributes. Then, a bright young Ugandan (Unlicensed userDaniel Kayiwa) suggested that we introduce the same flexibility of an entity-attribute-value (EAV) approach into the person table as we had done with our observations in the obs table. This approach allows implementations to virtually extend the person table to meet local needs. For example, in Tanzania, they wanted to track "ten cells", which are a type of addressing used in Tanzania. To accomplish this flexibility, we added a person_attribute table to contain implementation-specific data about persons and a person_attribute_type table to define the new "attributes" (virtual columns) for the person table. Using this mechanism, an implementation in Tanzania could define a new person attribute for "ten cell" and use it to store data for each person in their system without having to alter the core data model. Person attributes have been widely used & appreciated, since they allow OpenMRS to meet local needs through local extensions to the data model while allowing many implementations to continue sharing the core platform.
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