diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/AbstractValidator.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/AbstractValidator.java
index b875c4180a..ca4af8a1b8 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/AbstractValidator.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/AbstractValidator.java
@@ -12,6 +12,7 @@
 import com.mastercard.test.flow.Model;
 import com.mastercard.test.flow.validation.check.ChainOverlapCheck;
 import com.mastercard.test.flow.validation.check.DependencyChronologyCheck;
+import com.mastercard.test.flow.validation.check.DependencyInclusionCheck;
 import com.mastercard.test.flow.validation.check.DependencyLoopCheck;
 import com.mastercard.test.flow.validation.check.FlowIdentityCheck;
 import com.mastercard.test.flow.validation.check.InteractionIdentityCheck;
@@ -38,6 +39,7 @@ public static final Validation[] defaultChecks() {
 				new ChainOverlapCheck(),
 				new DependencyChronologyCheck(),
 				new DependencyLoopCheck(),
+				new DependencyInclusionCheck(),
 				new FlowIdentityCheck(),
 				new InteractionIdentityCheck(),
 				new MessageSharingCheck(),
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/Violation.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/Violation.java
index 5609e670b5..8acf223c65 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/Violation.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/Violation.java
@@ -26,12 +26,22 @@ public class Violation {
 	private final String actual;
 
 	/**
+	 * Constructs a new {@link Violation} that signals a general failure
+	 *
+	 * @param validation The {@link Validation} that has been violated
+	 * @param details    A human-readable description of the violation
+	 */
+	public Violation( Validation validation, String details ) {
+		this( validation, details, null, null );
+	}
+
+	/**
+	 * Constructs a new {@link Violation} that signals an expected-equality mismatch
+	 *
 	 * @param validation The {@link Validation} that has been violated
 	 * @param details    A human-readable description of the violation
-	 * @param expected   Expected half of a comparison test, or <code>null</code> to
-	 *                   just signal a general test failure
-	 * @param actual     Actual half of a comparison test, or <code>null</code>to
-	 *                   just signal a general test failure
+	 * @param expected   Expected half of an equality test
+	 * @param actual     Actual half of an equality test
 	 */
 	public Violation( Validation validation, String details, String expected, String actual ) {
 		this.validation = validation;
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ChainOverlapCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ChainOverlapCheck.java
index ad361381a4..0de145ed5c 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ChainOverlapCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ChainOverlapCheck.java
@@ -40,7 +40,7 @@ public Stream<Check> checks( Model model ) {
 							.collect( Collectors.toCollection( TreeSet::new ) );
 
 					if( chains.size() > 1 ) {
-						return new Violation( this, "Overlapping chains " + chains, null, null )
+						return new Violation( this, "Overlapping chains " + chains )
 								.offender( flow );
 					}
 
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyChronologyCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyChronologyCheck.java
index 8ac6ea6670..b1e382ad97 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyChronologyCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyChronologyCheck.java
@@ -48,11 +48,10 @@ public Stream<Check> checks( Model model ) {
 										+ "\nto\n"
 										+ "%s",
 										delorean.source().getMessage().map( Message::assertable ).orElse( "???" ),
-										delorean.sink().getMessage().map( Message::assertable ).orElse( "???" ) ),
-								null, null )
-										.offender( flow,
-												delorean.source().getInteraction().orElse( null ),
-												delorean.sink().getInteraction().orElse( null ) );
+										delorean.sink().getMessage().map( Message::assertable ).orElse( "???" ) ) )
+												.offender( flow,
+														delorean.source().getInteraction().orElse( null ),
+														delorean.sink().getInteraction().orElse( null ) );
 					}
 					return null;
 				} ) );
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheck.java
new file mode 100644
index 0000000000..7c6cdc7060
--- /dev/null
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheck.java
@@ -0,0 +1,51 @@
+package com.mastercard.test.flow.validation.check;
+
+import static java.util.stream.Collectors.toSet;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+import com.mastercard.test.flow.Dependency;
+import com.mastercard.test.flow.Flow;
+import com.mastercard.test.flow.Model;
+import com.mastercard.test.flow.validation.Check;
+import com.mastercard.test.flow.validation.Validation;
+import com.mastercard.test.flow.validation.Violation;
+
+/**
+ * Checks that the dependency flows are actually part of the system model
+ */
+public class DependencyInclusionCheck implements Validation {
+
+	@Override
+	public String name() {
+		return "Dependency inclusion";
+	}
+
+	@Override
+	public String explanation() {
+		return "Dependency sources must be included in the system model";
+	}
+
+	@Override
+	public Stream<Check> checks( Model model ) {
+		Set<Flow> allFlows = model.flows().collect( toSet() );
+		return model.flows()
+				.flatMap( Flow::dependencies )
+				.map( d -> new Check( this,
+						name( d ),
+						() -> d.source().getFlow()
+								.filter( src -> !allFlows.contains( src ) )
+								.map( src -> new Violation( this,
+										String.format( "Dependency source '%s' not presented in system model",
+												src.meta().id() ) )
+														.offender( d.sink().flow() ) )
+								.orElse( null ) ) );
+	}
+
+	private static String name( Dependency d ) {
+		return String.format( "%s → %s",
+				d.source().getFlow().map( f -> f.meta().id() ).orElse( null ),
+				d.sink().getFlow().map( f -> f.meta().id() ).orElse( null ) );
+	}
+}
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/FlowPairCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/FlowPairCheck.java
index b51eeb0e12..6cd53662f4 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/FlowPairCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/FlowPairCheck.java
@@ -51,7 +51,7 @@ public Stream<Check> checks( Model model ) {
 				checks.add( new Check( this,
 						left.meta().id() + " x " + right.meta().id(),
 						() -> violation( left, right )
-								.map( v -> new Violation( this, v, null, null )
+								.map( v -> new Violation( this, v )
 										.offender( left )
 										.offender( right ) )
 								.orElse( null ) ) );
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/InteractionIdentityCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/InteractionIdentityCheck.java
index 91d102c70c..0e43ffe711 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/InteractionIdentityCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/InteractionIdentityCheck.java
@@ -38,7 +38,7 @@ public Stream<Check> checks( Model model ) {
 								String id = String.format( "%s->%s %s",
 										ntr.requester().name(), ntr.responder().name(), ntr.tags() );
 								if( ids.containsKey( id ) ) {
-									return new Violation( this, "Shared interaction ID", null, null )
+									return new Violation( this, "Shared interaction ID" )
 											.offender( flow, ids.get( id ), ntr );
 								}
 								ids.put( id, ntr );
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/MessageSharingCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/MessageSharingCheck.java
index 1180633823..b1adf0580f 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/MessageSharingCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/MessageSharingCheck.java
@@ -50,10 +50,9 @@ public Stream<Check> checks( Model model ) {
 							MessageOwner current = new MessageOwner( flow, tx.source() );
 							MessageOwner previous = messageIdentities.get( objectId );
 							if( previous != null ) {
-								return new Violation( this, "Shared message:\n" + tx.message().assertable(),
-										null, null )
-												.offender( previous.flow, previous.interaction )
-												.offender( current.flow, current.interaction );
+								return new Violation( this, "Shared message:\n" + tx.message().assertable() )
+										.offender( previous.flow, previous.interaction )
+										.offender( current.flow, current.interaction );
 							}
 							messageIdentities.put( objectId, current );
 						}
diff --git a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ResultTagCheck.java b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ResultTagCheck.java
index 510eb6233b..88469aba3f 100644
--- a/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ResultTagCheck.java
+++ b/validation/validation-core/src/main/java/com/mastercard/test/flow/validation/check/ResultTagCheck.java
@@ -54,7 +54,7 @@ public Stream<Check> checks( Model model ) {
 							.collect( Collectors.joining( ", " ) );
 
 					if( !misused.isEmpty() ) {
-						return new Violation( this, "Use of reserved tags: " + misused, null, null )
+						return new Violation( this, "Use of reserved tags: " + misused )
 								.offender( flow );
 					}
 
diff --git a/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/AbstractValidatorTest.java b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/AbstractValidatorTest.java
index 3e59f67ce7..7c3621b428 100644
--- a/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/AbstractValidatorTest.java
+++ b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/AbstractValidatorTest.java
@@ -31,6 +31,7 @@ void with() {
 		Assertions.assertEquals( ""
 				+ "Chain overlap\n"
 				+ "Dependency chronology\n"
+				+ "Dependency inclusion\n"
 				+ "Dependency loop\n"
 				+ "Flow Identity\n"
 				+ "Interaction Identity\n"
@@ -62,9 +63,9 @@ void acceptance() {
 				.accepting( v -> v.details().contains( "minor" ) );
 
 		Assertions.assertFalse( tv.accepted(
-				new Violation( null, "gadzooks! this is a major problem!", null, null ) ) );
+				new Violation( null, "gadzooks! this is a major problem!" ) ) );
 		Assertions.assertTrue( tv.accepted(
-				new Violation( null, "meh, this is a minor problem", null, null ) ) );
+				new Violation( null, "meh, this is a minor problem" ) ) );
 
 	}
 }
diff --git a/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheckTest.java b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheckTest.java
new file mode 100644
index 0000000000..df432200e0
--- /dev/null
+++ b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyInclusionCheckTest.java
@@ -0,0 +1,193 @@
+package com.mastercard.test.flow.validation.check;
+
+import static java.util.Collections.emptySet;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import com.mastercard.test.flow.Dependency;
+import com.mastercard.test.flow.FieldAddress;
+import com.mastercard.test.flow.Flow;
+import com.mastercard.test.flow.Metadata;
+import com.mastercard.test.flow.Model;
+
+/**
+ * Exercises {@link DependencyInclusionCheck}
+ */
+class DependencyInclusionCheckTest extends AbstractValidationTest {
+
+	/***/
+	DependencyInclusionCheckTest() {
+		super( new DependencyInclusionCheck(),
+				"Dependency inclusion",
+				"Dependency sources must be included in the system model" );
+	}
+
+	/**
+	 * No flows
+	 */
+	@Test
+	void empty() {
+		test( mdl( flws().values() ) );
+	}
+
+	/**
+	 * A single flow
+	 */
+	@Test
+	void lonesome() {
+		test( mdl( flws( "lonely" ).values() ) );
+	}
+
+	/**
+	 * Two flows, but no dependencies
+	 */
+	@Test
+	void noDependencies() {
+		test( mdl( flws( "abc", "def" ).values() ) );
+	}
+
+	/**
+	 * Two flows, a dependency, the sink is included in the model
+	 */
+	@Test
+	void included() {
+		test( mdl( flws( "abc", "def abc" ).values() ),
+				"abc [] → def [] : pass" );
+	}
+
+	/**
+	 * Two flows, a dependency, the sink is <i>not</i> included in the model
+	 */
+	@Test
+	void excluded() {
+		Map<String, Flow> flows = flws( "abc", "def abc" );
+		flows.remove( "abc" );
+		test( mdl( flows.values() ),
+				"  details: Dependency source 'abc []' not presented in system model\n"
+						+ " expected: null\n"
+						+ "   actual: null\n"
+						+ "offenders: def []\n"
+						+ "null" );
+	}
+
+	/**
+	 * One valid dependency, one violation
+	 */
+	@Test
+	void mixed() {
+		Map<String, Flow> flows = flws(
+				"abc", "def abc",
+				"ghi", "jkl ghi" );
+		flows.remove( "ghi" );
+		test( mdl( flows.values() ),
+				"abc [] → def [] : pass",
+				"  details: Dependency source 'ghi []' not presented in system model\n"
+						+ " expected: null\n"
+						+ "   actual: null\n"
+						+ "offenders: jkl []\n"
+						+ "null" );
+	}
+
+	/**
+	 * Multiple valid dependencies
+	 */
+	@Test
+	void multiIncluded() {
+		test( mdl( flws( "abc", "def abc", "ghi abc def", "jkl abc def ghi" ).values() ),
+				"abc [] → def [] : pass",
+				"abc [] → ghi [] : pass",
+				"def [] → ghi [] : pass",
+				"abc [] → jkl [] : pass",
+				"def [] → jkl [] : pass",
+				"ghi [] → jkl [] : pass" );
+	}
+
+	/**
+	 * Multiple invalid dependencies
+	 */
+	@Test
+	void multiExcluded() {
+		Map<String, Flow> flows = flws( "abc", "def abc", "ghi abc def", "jkl abc def ghi" );
+		flows.remove( "def" );
+		test( mdl( flows.values() ),
+				"abc [] → ghi [] : pass",
+				"  details: Dependency source 'def []' not presented in system model\n"
+						+ " expected: null\n"
+						+ "   actual: null\n"
+						+ "offenders: ghi []\n"
+						+ "null",
+				"abc [] → jkl [] : pass",
+				"  details: Dependency source 'def []' not presented in system model\n"
+						+ " expected: null\n"
+						+ "   actual: null\n"
+						+ "offenders: jkl []\n"
+						+ "null",
+				"ghi [] → jkl [] : pass" );
+	}
+
+	/**
+	 * @param flows A set of strings, each specifying one flow. The strings are
+	 *              space-separated lists. The first element is the flow name, the
+	 *              following elements are the names of dependency flows
+	 * @return A model, with the specified flows and dependency structure
+	 */
+	private static Map<String, Flow> flws( String... flows ) {
+		Map<String, Flow> names = new HashMap<>();
+
+		for( String flow : flows ) {
+			String[] tkns = flow.split( " " );
+
+			Flow flw = Mockito.mock( Flow.class );
+			Metadata mtdt = Mockito.mock( Metadata.class );
+
+			when( mtdt.description() ).thenReturn( tkns[0] );
+			when( mtdt.tags() ).thenReturn( emptySet() );
+			when( mtdt.id() ).thenCallRealMethod();
+			when( flw.meta() ).thenReturn( mtdt );
+
+			List<Dependency> deps = new ArrayList<>();
+			for( int i = 1; i < tkns.length; i++ ) {
+				String depName = tkns[i];
+
+				FieldAddress src = mock( FieldAddress.class );
+				when( src.getFlow() ).thenReturn( Optional.ofNullable( names.get( depName ) ) );
+				when( src.flow() ).thenAnswer( a -> names.get( depName ) );
+
+				FieldAddress snk = mock( FieldAddress.class );
+				when( snk.getFlow() ).thenReturn( Optional.of( flw ) );
+				when( snk.flow() ).thenReturn( flw );
+
+				Dependency dep = mock( Dependency.class );
+				when( dep.source() ).thenReturn( src );
+				when( dep.sink() ).thenReturn( snk );
+
+				deps.add( dep );
+			}
+			when( flw.dependencies() ).thenAnswer( a -> deps.stream() );
+
+			names.put( tkns[0], flw );
+		}
+
+		return names;
+	}
+
+	/**
+	 * @param flows Some {@link Flow}s
+	 * @return a {@link Model} that produces the supplied {@link Flow}s
+	 */
+	private static Model mdl( Collection<Flow> flows ) {
+		Model mdl = Mockito.mock( Model.class );
+		when( mdl.flows() ).thenAnswer( a -> flows.stream() );
+		return mdl;
+	}
+}
diff --git a/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyLoopCheckTest.java b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyLoopCheckTest.java
index 4bb694ff8d..6e9422c3da 100644
--- a/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyLoopCheckTest.java
+++ b/validation/validation-core/src/test/java/com/mastercard/test/flow/validation/check/DependencyLoopCheckTest.java
@@ -175,7 +175,7 @@ void lollipop() {
 	}
 
 	/**
-	 * @param flows A set of string, each specifying one flow. The strings are
+	 * @param flows A set of strings, each specifying one flow. The strings are
 	 *              space-separated lists. The first element is the flow name, the
 	 *              following elements are the names of dependency flows
 	 * @return A model, with the specified flows and dependency structure
diff --git a/validation/validation-junit4/src/test/java/com/mastercard/test/flow/validation/junit4/ExampleTest.java b/validation/validation-junit4/src/test/java/com/mastercard/test/flow/validation/junit4/ExampleTest.java
index b455901f5b..db6a7c89f9 100644
--- a/validation/validation-junit4/src/test/java/com/mastercard/test/flow/validation/junit4/ExampleTest.java
+++ b/validation/validation-junit4/src/test/java/com/mastercard/test/flow/validation/junit4/ExampleTest.java
@@ -139,7 +139,7 @@ public String explanation() {
 			public Stream<Check> checks( Model model ) {
 				return Stream.of(
 						new Check( this, "fail",
-								() -> new Violation( this, "fail", null, null ) ),
+								() -> new Violation( this, "fail" ) ),
 						new Check( this, "cmp fail",
 								() -> new Violation( this, "fail", "expect", "actual" ) ) );
 			}
@@ -163,7 +163,7 @@ public String explanation() {
 			public Stream<Check> checks( Model model ) {
 				return Stream.of(
 						new Check( this, "accept",
-								() -> new Violation( this, "accept", null, null ) ) );
+								() -> new Violation( this, "accept" ) ) );
 			}
 		};
 	}
diff --git a/validation/validation-junit5/src/test/java/com/mastercard/test/flow/validation/junit5/ExampleTest.java b/validation/validation-junit5/src/test/java/com/mastercard/test/flow/validation/junit5/ExampleTest.java
index 937ab24a2b..aa37dc9bd3 100644
--- a/validation/validation-junit5/src/test/java/com/mastercard/test/flow/validation/junit5/ExampleTest.java
+++ b/validation/validation-junit5/src/test/java/com/mastercard/test/flow/validation/junit5/ExampleTest.java
@@ -116,7 +116,7 @@ public String explanation() {
 			public Stream<Check> checks( Model model ) {
 				return Stream.of(
 						new Check( this, "fail",
-								() -> new Violation( this, "fail", null, null ) ),
+								() -> new Violation( this, "fail" ) ),
 						new Check( this, "cmp fail",
 								() -> new Violation( this, "fail", "expect", "actual" ) ) );
 			}
@@ -140,7 +140,7 @@ public String explanation() {
 			public Stream<Check> checks( Model model ) {
 				return Stream.of(
 						new Check( this, "accept",
-								() -> new Violation( this, "accept", null, null ) ) );
+								() -> new Violation( this, "accept" ) ) );
 			}
 		};
 	}