diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/Emission.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/Emission.java
index 69a50b9aa..a80bacd19 100644
--- a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/Emission.java
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/Emission.java
@@ -13,6 +13,7 @@
 package org.eclipse.passage.lic.internal.api.conditions.evaluation;
 
 import java.util.Collection;
+import java.util.Objects;
 
 /**
  * Report {@linkplain Condition}s evaluation results.
@@ -51,6 +52,7 @@ public static final class Successful implements Emission {
 		private final Collection<Permission> permissions;
 
 		public Successful(Collection<Permission> permissions) {
+			Objects.requireNonNull(permissions, "Emission.Successful::permissions"); //$NON-NLS-1$
 			this.permissions = permissions;
 		}
 
@@ -76,6 +78,7 @@ public static final class Failed implements Emission {
 		private final EmissionFailureDiagnostic diagnose;
 
 		public Failed(EmissionFailureDiagnostic diagnose) {
+			Objects.requireNonNull(diagnose, "Emission.Failed::diagnose"); //$NON-NLS-1$
 			this.diagnose = diagnose;
 		}
 
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluationService.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluationService.java
new file mode 100644
index 000000000..935f1cfed
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluationService.java
@@ -0,0 +1,21 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import org.eclipse.passage.lic.internal.api.registry.Service;
+
+public interface ExpressionEvaluationService extends Service<ExpressionProtocol> {
+
+	boolean evaluate(ParsedExpression expression, ExpressionTokenAssessmentService assessor);
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluatorsRegistry.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluatorsRegistry.java
new file mode 100644
index 000000000..88ecb514e
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionEvaluatorsRegistry.java
@@ -0,0 +1,22 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import java.util.function.Supplier;
+
+import org.eclipse.passage.lic.internal.api.registry.Registry;
+
+public interface ExpressionEvaluatorsRegistry
+		extends Supplier<Registry<ExpressionProtocol, ExpressionEvaluationService>> {
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionParsingException.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionParsingException.java
new file mode 100644
index 000000000..caa25c2a3
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionParsingException.java
@@ -0,0 +1,26 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+@SuppressWarnings("serial")
+public final class ExpressionParsingException extends Exception {
+
+	public ExpressionParsingException(String message, Throwable cause) {
+		super(message, cause);
+	}
+
+	public ExpressionParsingException(String message) {
+		super(message);
+	}
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringRegistry.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringRegistry.java
new file mode 100644
index 000000000..cba61958a
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringRegistry.java
@@ -0,0 +1,21 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import java.util.function.Supplier;
+
+import org.eclipse.passage.lic.internal.api.registry.Registry;
+
+public interface ExpressionPasringRegistry extends Supplier<Registry<ExpressionProtocol, ExpressionPasringService>> {
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringService.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringService.java
new file mode 100644
index 000000000..e3281388b
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionPasringService.java
@@ -0,0 +1,21 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import org.eclipse.passage.lic.internal.api.registry.Service;
+
+public interface ExpressionPasringService extends Service<ExpressionProtocol> {
+
+	ParsedExpression parsed(String expression) throws ExpressionParsingException;
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionProtocol.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionProtocol.java
new file mode 100644
index 000000000..8e7fb8b33
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionProtocol.java
@@ -0,0 +1,74 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import java.util.Objects;
+
+import org.eclipse.passage.lic.internal.api.registry.ServiceId;
+
+public abstract class ExpressionProtocol implements ServiceId {
+
+	private final String identifier;
+
+	protected ExpressionProtocol(String identifier) {
+		Objects.requireNonNull(identifier, "ExpressionProtocol::identifier"); //$NON-NLS-1$
+		this.identifier = identifier.trim().toLowerCase();
+	}
+
+	public final String identifier() {
+		return identifier;
+	}
+
+	@Override
+	public final int hashCode() {
+		return Objects.hash(identifier());
+	}
+
+	@Override
+	public final boolean equals(Object object) {
+		if (!ExpressionProtocol.class.isInstance(object)) {
+			return false;
+		}
+		return identifier.equals(((ExpressionProtocol) object).identifier);
+	}
+
+	@Override
+	public final String toString() {
+		return identifier;
+	}
+
+	public static final class Ands extends ExpressionProtocol {
+
+		public Ands() {
+			super("ands"); //$NON-NLS-1$
+		}
+
+	}
+
+	public static final class Default extends ExpressionProtocol {
+
+		public Default() {
+			super(new Ands().identifier());
+		}
+
+	}
+
+	public static final class Of extends ExpressionProtocol {
+
+		public Of(String identifier) {
+			super(identifier);
+		}
+
+	}
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessmentService.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessmentService.java
new file mode 100644
index 000000000..6159fa8c7
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessmentService.java
@@ -0,0 +1,45 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import org.eclipse.passage.lic.internal.api.conditions.EvaluationType;
+import org.eclipse.passage.lic.internal.api.registry.Service;
+
+/**
+ * <p>
+ * Condition expression parsing, depending on the protocol used, can boil down
+ * to a sophisticated construction of predicates.
+ * </p>
+ * <p>
+ * But at the bottom of the evaluation of such a construction there are quite
+ * simple questions for the runtime environment: is current operating system is
+ * Linux-like? is the hard disk serial equal to this precise value? - that kind
+ * of asking.
+ * </p>
+ * <p>
+ * Implementation of this interface for a particular {@linkplain EvaluationType}
+ * must answer only these simple questions. the rest of the evaluation logic is
+ * on {@linkplain ExpressionProtocol}-aware services.
+ * </p>
+ */
+public interface ExpressionTokenAssessmentService extends Service<EvaluationType> {
+
+	boolean equal(String key, String value);
+
+	// contains ()
+
+	// startsWith ()
+
+	// all the things we will ever need -> slice to [Operation]s
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessorsRegistry.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessorsRegistry.java
new file mode 100644
index 000000000..2bf8e9d1a
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ExpressionTokenAssessorsRegistry.java
@@ -0,0 +1,23 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+import java.util.function.Supplier;
+
+import org.eclipse.passage.lic.internal.api.conditions.EvaluationType;
+import org.eclipse.passage.lic.internal.api.registry.Registry;
+
+public interface ExpressionTokenAssessorsRegistry
+		extends Supplier<Registry<EvaluationType, ExpressionTokenAssessmentService>> {
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ParsedExpression.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ParsedExpression.java
new file mode 100644
index 000000000..d4e3d2a80
--- /dev/null
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/ParsedExpression.java
@@ -0,0 +1,19 @@
+/*******************************************************************************
+ * Copyright (c) 2020 ArSysOp
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * https://www.eclipse.org/legal/epl-2.0/.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     ArSysOp - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.passage.lic.internal.api.conditions.evaluation;
+
+public interface ParsedExpression {
+
+	ExpressionProtocol protocol();
+
+}
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissionsRegistry.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittersRegistry.java
similarity index 86%
rename from bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissionsRegistry.java
rename to bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittersRegistry.java
index b531c4a0b..5f2b4dc5e 100644
--- a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissionsRegistry.java
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittersRegistry.java
@@ -17,6 +17,6 @@
 import org.eclipse.passage.lic.internal.api.registry.Registry;
 import org.eclipse.passage.lic.internal.api.registry.StringServiceId;
 
-public interface EmittedPermissionsRegistry extends Supplier<Registry<StringServiceId, EmittedPermissions>> {
+public interface PermissionEmittersRegistry extends Supplier<Registry<StringServiceId, PermissionEmittingService>> {
 
 }
diff --git a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissions.java b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittingService.java
similarity index 93%
rename from bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissions.java
rename to bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittingService.java
index a29fe6c83..fceb0accf 100644
--- a/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/EmittedPermissions.java
+++ b/bundles/org.eclipse.passage.lic.api/src/org/eclipse/passage/lic/internal/api/conditions/evaluation/PermissionEmittingService.java
@@ -19,7 +19,7 @@
 import org.eclipse.passage.lic.internal.api.registry.Service;
 import org.eclipse.passage.lic.internal.api.registry.StringServiceId;
 
-public interface EmittedPermissions extends Service<StringServiceId> {
+public interface PermissionEmittingService extends Service<StringServiceId> {
 
 	/**
 	 * <p>
@@ -47,6 +47,6 @@ public interface EmittedPermissions extends Service<StringServiceId> {
 	 * reported in the returned {@linkplain Emission} instance.
 	 * </p>
 	 */
-	Emission get(Collection<Condition> conditions, LicensedProduct product);
+	Emission emit(Collection<Condition> conditions, LicensedProduct product);
 
 }