diff --git a/doc/observed_data.plantuml b/doc/observed_data.plantuml
new file mode 100644
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+++ b/doc/observed_data.plantuml
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+@startuml
+left to right direction
+
+RigSummaryCaseData *-- "1" RifSummaryReaderInterface
+RimSummaryCase *-- "1" RigSummaryCaseData
+
+RifSummaryReaderInterface <|-- RifReaderEclipseSummary
+RifSummaryReaderInterface <|-- RifReaderObservedData
+
+RifReaderObservedData *-- "N" RifColumnBasedAsciiParser
+
+RimSummaryCase <|-- RimFileSummaryCase
+RimSummaryCase <|-- RimObservedData
+
+RimObservedData <|-- RimSummaryObservedDataFile
+
+
+@enduml