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The Standardized Vocabularies are constructed with a few principles in mind. Not every principle can be executed to perfection, but it represents a general motivation and direction of the ongoing improvement and development process:
The top-down problem has the additional difficulty in that Classifications are not always agreed upon in the scientific community. For example, whether diabetic complications are part of the Condition “Diabetes” or are separate entities is differently answered by the SNOMED and ICD-9 hierarchies, respectively.