merge: Introduce schema for trace API (#88)

This pull request updates the OpenDC trace API to support proper specification 
of a schema of the tables exposed by the traces. This functionality makes it easier 
for the API consumer to understand the types exposed by the API.

## Implementation Notes :hammer_and_pick:

* Introduce type system for trace API
* Add benchmarks for odcvm trace format 
* Add benchmarks for Azure trace format
* Add conformance suite for OpenDC trace API 

## External Dependencies :four_leaf_clover:

* N/A

## Breaking API Changes :warning:

* Removal of typed `TableColumn`. Instead, `TableColumn` instances are now 
   used to describe the columns belonging to some table.
* `TableReader` and `TableWriter` do not support accessing arbitrary objects 
   anymore. Instead, only the types supported by the type system are exposed.

1 files changed, 9 insertions, 41 deletions

diff --git a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/TableColumn.kt b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/TableColumn.kt
index b77a2982..0f75d890 100644
--- a/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/TableColumn.kt
+++ b/opendc-trace/opendc-trace-api/src/main/kotlin/org/opendc/trace/TableColumn.kt
@@ -22,47 +22,15 @@
 
 package org.opendc.trace
 
-import java.util.*
-
 /**
- * A column in a trace table.
+ * A column in a [Table].
  *
- * @param name The universal name of this column.
+ * @property name The universal name of this column.
+ * @property type The type of the column.
+ * @property isNullable A flag to indicate that the column is nullable.
  */
-public class TableColumn<out T>(public val name: String, type: Class<T>) {
-    /**
-     * The type of the column.
-     */
-    public val type: Class<*> = type
-
-    /**
-     * Determine whether the type of the column is a subtype of [column].
-     */
-    public fun isAssignableTo(column: TableColumn<*>): Boolean {
-        return name == column.name && type.isAssignableFrom(column.type)
-    }
-
-    /**
-     * Compute a hash code for this column.
-     */
-    public override fun hashCode(): Int = Objects.hash(name, type)
-
-    /**
-     * Determine whether this column is equal to [other].
-     */
-    public override fun equals(other: Any?): Boolean {
-        // Fast-path: reference equality
-        if (this === other) {
-            return true
-        } else if (other == null || other !is TableColumn<*>) {
-            return false
-        }
-
-        return name == other.name && type == other.type
-    }
-
-    /**
-     * Return a string representation of this column.
-     */
-    public override fun toString(): String = "TableColumn[$name,$type]"
-}
+public data class TableColumn(
+    public val name: String,
+    public val type: TableColumnType,
+    public val isNullable: Boolean = false
+)