a start

src/SIL.Machine/Translation/IInteractiveTranslationModel.cs

@@ -3,7 +3,7 @@
 
 namespace SIL.Machine.Translation
 {
-    public interface IInteractiveTranslationModel : IInteractiveTranslationEngine, ITranslationModel
+    public interface IInteractiveTranslationModel : IInteractiveTranslationEngine, IWordAlignerEngine, ITranslationModel
     {
         Task SaveAsync(CancellationToken cancellationToken = default);
         void Save();

src/SIL.Machine/Translation/IWordAlignerEngine.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SIL.Machine.Translation
+{
+    public interface IWordAlignerEngine : IDisposable
+    {
+        Task<TranslationResult> GetBestPhraseAlignmentAsync(
+            string sourceSegment,
+            string targetSegment,
+            CancellationToken cancellationToken = default
+        );
+
+        Task<TranslationResult> GetBestPhraseAlignmentAsync(
+            IReadOnlyList<string> sourceSegment,
+            IReadOnlyList<string> targetSegment,
+            CancellationToken cancellationToken = default
+        );
+
+        TranslationResult GetBestPhraseAlignment(string sourceSegment, string targetSegment);
+
+        TranslationResult GetBestPhraseAlignment(
+            IReadOnlyList<string> sourceSegment,
+            IReadOnlyList<string> targetSegment
+        );
+    }
+}