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dataframe/docs/StardustDocs/topics/schemas/schemasInheritance.md

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+[//]: # (title: Schema inheritance)
+
+<!---IMPORT org.jetbrains.kotlinx.dataframe.samples.api.Schemas-->
+
+In order to reduce amount of generated code, previously generated [`DataSchema`](schema.md) interfaces are reused and only new
+properties are introduced
+
+Let's filter out all `null` values from `age` column and add one more column of type `Boolean`:
+
+```kotlin
+val filtered = df.filter { age != null }.add("isAdult") { age!! > 18 }
+```
+
+New schema interface for `filtered` variable will be derived from previously generated `DataFrameType`:
+
+```kotlin
+@DataSchema
+interface DataFrameType1 : DataFrameType
+```
+
+Extension properties for data access are generated only for new and overridden members of `DataFrameType1` interface:
+
+```kotlin
+val ColumnsContainer<DataFrameType1>.age: DataColumn<Int> get() = this["age"] as DataColumn<Int>
+val DataRow<DataFrameType1>.age: Int get() = this["age"] as Int
+val ColumnsContainer<DataFrameType1>.isAdult: DataColumn<Boolean> get() = this["isAdult"] as DataColumn<Boolean>
+val DataRow<DataFrameType1>.isAdult: String get() = this["isAdult"] as Boolean
+```
+
+Then variable `filtered` is cast to new interface:
+
+```kotlin
+val temp = filtered
+```
+
+```kotlin
+val filtered = temp.cast<DataFrameType1>()
+```