diff --git a/include/plasp/pddl/Context.h b/include/plasp/pddl/Context.h
index 5a3cd52..95c3529 100644
--- a/include/plasp/pddl/Context.h
+++ b/include/plasp/pddl/Context.h
@@ -1,6 +1,10 @@
 #ifndef __PLASP__PDDL__CONTEXT_H
 #define __PLASP__PDDL__CONTEXT_H
 
+#include <memory>
+#include <unordered_map>
+#include <vector>
+
 #include <plasp/pddl/Predicate.h>
 #include <plasp/pddl/Type.h>
 
@@ -18,8 +22,13 @@ namespace pddl
 class Context
 {
 	public:
-		TypeHashMap types;
-		PredicateHashMap predicates;
+		std::vector<std::unique_ptr<PrimitiveType>> primitiveTypes;
+		std::unordered_map<std::string, PrimitiveType *> primitiveTypesHashMap;
+
+		std::vector<std::unique_ptr<EitherType>> eitherTypes;
+
+		std::vector<std::unique_ptr<Predicate>> predicates;
+		std::unordered_map<PredicateHashMapKey, Predicate *> predicatesHashMap;
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/include/plasp/pddl/Domain.h b/include/plasp/pddl/Domain.h
index 61f6519..914284b 100644
--- a/include/plasp/pddl/Domain.h
+++ b/include/plasp/pddl/Domain.h
@@ -28,8 +28,8 @@ class Domain
 	public:
 		const std::string &name() const;
 		const Requirements &requirements() const;
-		const TypeHashMap &types() const;
-		const PredicateHashMap &predicates() const;
+		const std::vector<std::unique_ptr<PrimitiveType>> &types() const;
+		const std::vector<std::unique_ptr<Predicate>> &predicates() const;
 
 	private:
 		Domain(Context &context);
@@ -40,7 +40,7 @@ class Domain
 		bool hasRequirement(Requirement::Type requirementType) const;
 		void computeDerivedRequirements();
 
-		void parseTypingSection(utils::Parser &parser);
+		void parseTypeSection(utils::Parser &parser);
 
 		void parsePredicateSection(utils::Parser &parser);
 
diff --git a/include/plasp/pddl/EitherType.h b/include/plasp/pddl/EitherType.h
new file mode 100644
index 0000000..6118607
--- /dev/null
+++ b/include/plasp/pddl/EitherType.h
@@ -0,0 +1,43 @@
+#ifndef __PLASP__PDDL__EITHER_TYPE_H
+#define __PLASP__PDDL__EITHER_TYPE_H
+
+#include <vector>
+
+#include <plasp/pddl/PrimitiveType.h>
+#include <plasp/utils/Parser.h>
+
+namespace plasp
+{
+namespace pddl
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// EitherType
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class Context;
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class EitherType
+{
+	public:
+		static EitherType &parse(utils::Parser &parser, Context &context);
+
+	public:
+		const std::vector<const PrimitiveType *> &allowedTypes() const;
+
+	private:
+		EitherType() = default;
+
+		std::vector<const PrimitiveType *> m_allowedTypes;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
+
+#endif
diff --git a/include/plasp/pddl/Predicate.h b/include/plasp/pddl/Predicate.h
index 17daa79..d1bd27d 100644
--- a/include/plasp/pddl/Predicate.h
+++ b/include/plasp/pddl/Predicate.h
@@ -1,7 +1,6 @@
 #ifndef __PLASP__PDDL__PREDICATE_H
 #define __PLASP__PDDL__PREDICATE_H
 
-#include <unordered_map>
 #include <vector>
 
 #include <boost/functional/hash.hpp>
@@ -33,9 +32,6 @@ struct PredicateHashMapKey
 	}
 };
 
-class Predicate;
-using PredicateHashMap = std::unordered_map<PredicateHashMapKey, Predicate>;
-
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
 class Predicate
diff --git a/include/plasp/pddl/PrimitiveType.h b/include/plasp/pddl/PrimitiveType.h
index 59fdc30..0f33657 100644
--- a/include/plasp/pddl/PrimitiveType.h
+++ b/include/plasp/pddl/PrimitiveType.h
@@ -1,5 +1,5 @@
-#ifndef __PLASP__PDDL__TYPE_PRIMITIVE_H
-#define __PLASP__PDDL__TYPE_PRIMITIVE_H
+#ifndef __PLASP__PDDL__PRIMITIVE_TYPE_H
+#define __PLASP__PDDL__PRIMITIVE_TYPE_H
 
 #include <string>
 #include <vector>
@@ -13,7 +13,7 @@ namespace pddl
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 //
-// TypePrimitive
+// PrimitiveType
 //
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -21,34 +21,34 @@ class Context;
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-class TypePrimitive
+class PrimitiveType
 {
 	public:
-		static TypePrimitive &parse(utils::Parser &parser, Context &context);
-		static TypePrimitive &parseDeclaration(utils::Parser &parser, Context &context);
+		static PrimitiveType &parse(utils::Parser &parser, Context &context);
+		static PrimitiveType &parseDeclaration(utils::Parser &parser, Context &context);
 
 	public:
 		const std::string &name() const;
-		const std::vector<const TypePrimitive *> &parentTypes() const;
+		const std::vector<const PrimitiveType *> &parentTypes() const;
 
 		bool isDeclared() const;
 
 	private:
-		TypePrimitive(std::string name);
+		PrimitiveType(std::string name);
 
 		void setDirty(bool isDirty = true);
 		bool isDirty() const;
 
 		void setDeclared();
 
-		void addParentType(const TypePrimitive &parentType);
+		void addParentType(const PrimitiveType &parentType);
 
 		bool m_isDirty;
 		bool m_isDeclared;
 
 		std::string m_name;
 
-		std::vector<const TypePrimitive *> m_parentTypes;
+		std::vector<const PrimitiveType *> m_parentTypes;
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/include/plasp/pddl/Type.h b/include/plasp/pddl/Type.h
index f6f6756..ddda7b9 100644
--- a/include/plasp/pddl/Type.h
+++ b/include/plasp/pddl/Type.h
@@ -1,11 +1,10 @@
 #ifndef __PLASP__PDDL__TYPE_H
 #define __PLASP__PDDL__TYPE_H
 
-#include <unordered_map>
-
 #include <boost/variant.hpp>
 
-#include <plasp/pddl/TypePrimitive.h>
+#include <plasp/pddl/EitherType.h>
+#include <plasp/pddl/PrimitiveType.h>
 
 namespace plasp
 {
@@ -18,8 +17,7 @@ namespace pddl
 //
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-using Type = boost::variant<TypePrimitive>;
-using TypeHashMap = std::unordered_map<std::string, Type>;
+using TypePtr = boost::variant<const PrimitiveType *, const EitherType *>;
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
diff --git a/include/plasp/pddl/Variable.h b/include/plasp/pddl/Variable.h
index c820d51..6ea62a3 100644
--- a/include/plasp/pddl/Variable.h
+++ b/include/plasp/pddl/Variable.h
@@ -31,12 +31,12 @@ class Variable
 
 	public:
 		const std::string &name() const;
-		const Type &type() const;
+		TypePtr type() const;
 
 		void setDirty(bool isDirty = true);
 		bool isDirty() const;
 
-		void setType(const Type &type);
+		void setType(TypePtr type);
 
 	private:
 		Variable(std::string name);
@@ -45,7 +45,7 @@ class Variable
 
 		std::string m_name;
 
-		const Type *m_type;
+		TypePtr m_type;
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/src/plasp/pddl/Domain.cpp b/src/plasp/pddl/Domain.cpp
index 611a613..c2ea837 100644
--- a/src/plasp/pddl/Domain.cpp
+++ b/src/plasp/pddl/Domain.cpp
@@ -67,14 +67,14 @@ const Requirements &Domain::requirements() const
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-const TypeHashMap &Domain::types() const
+const std::vector<std::unique_ptr<PrimitiveType>> &Domain::types() const
 {
-	return m_context.types;
+	return m_context.primitiveTypes;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-const PredicateHashMap &Domain::predicates() const
+const std::vector<std::unique_ptr<Predicate>> &Domain::predicates() const
 {
 	return m_context.predicates;
 }
@@ -114,7 +114,7 @@ void Domain::parseSection(utils::Parser &parser)
 	if (sectionIdentifier == "requirements")
 		parseRequirementsSection(parser);
 	else if (sectionIdentifier == "types")
-		parseTypingSection(parser);
+		parseTypeSection(parser);
 	else if (sectionIdentifier == "constants")
 		skipSection();
 	else if (sectionIdentifier == "predicates")
@@ -208,14 +208,17 @@ void Domain::computeDerivedRequirements()
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void Domain::parseTypingSection(utils::Parser &parser)
+void Domain::parseTypeSection(utils::Parser &parser)
 {
 	parser.skipWhiteSpace();
 
 	// Store types and their parent types
 	while (parser.currentCharacter() != ')')
 	{
-		TypePrimitive::parseDeclaration(parser, m_context);
+		if (parser.currentCharacter() == '(')
+			throw utils::ParserException(parser.row(), parser.column(), "Only primitive types are allowed in type section");
+
+		PrimitiveType::parseDeclaration(parser, m_context);
 
 		parser.skipWhiteSpace();
 	}
@@ -245,7 +248,7 @@ void Domain::parsePredicateSection(utils::Parser &parser)
 void Domain::checkConsistency()
 {
 	// Verify that typing requirement is correctly declared if used
-	if (!m_context.types.empty() && !hasRequirement(Requirement::Type::Typing))
+	if (!m_context.primitiveTypes.empty() && !hasRequirement(Requirement::Type::Typing))
 	{
 		throw ConsistencyException("Domain contains typing information but does not declare typing requirement");
 
@@ -253,25 +256,19 @@ void Domain::checkConsistency()
 	}
 
 	// Verify that all used types have been declared
-	std::for_each(m_context.types.cbegin(), m_context.types.cend(),
+	std::for_each(m_context.primitiveTypes.cbegin(), m_context.primitiveTypes.cend(),
 		[&](const auto &type)
 		{
-			// TODO: refactor without typeinfo
-			if (type.second.type() != boost::typeindex::type_id<TypePrimitive>())
-				return;
-
-			const auto &typePrimitive = boost::get<TypePrimitive>(type.second);
-
-			if (!typePrimitive.isDeclared())
-				throw ConsistencyException("Type \"" + typePrimitive.name() + "\" used but never declared");
+			if (!type->isDeclared())
+				throw ConsistencyException("Type \"" + type->name() + "\" used but never declared");
 		});
 
 	// Verify that all used predicates have been declared
 	std::for_each(m_context.predicates.cbegin(), m_context.predicates.cend(),
 		[&](const auto &predicate)
 		{
-			if (!predicate.second.isDeclared())
-				throw ConsistencyException("Predicate \"" + predicate.second.name() + "\" used but never declared");
+			if (!predicate->isDeclared())
+				throw ConsistencyException("Predicate \"" + predicate->name() + "\" used but never declared");
 		});
 
 	// Verify that all variables have types
diff --git a/src/plasp/pddl/EitherType.cpp b/src/plasp/pddl/EitherType.cpp
new file mode 100644
index 0000000..42d2d34
--- /dev/null
+++ b/src/plasp/pddl/EitherType.cpp
@@ -0,0 +1,52 @@
+#include <plasp/pddl/EitherType.h>
+
+#include <algorithm>
+
+#include <plasp/pddl/Context.h>
+#include <plasp/pddl/Identifier.h>
+
+namespace plasp
+{
+namespace pddl
+{
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// EitherType
+//
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+EitherType &EitherType::parse(utils::Parser &parser, Context &context)
+{
+	parser.skipWhiteSpace();
+
+	auto eitherType = std::make_unique<EitherType>(EitherType());
+
+	parser.expect<std::string>("(either");
+	parser.skipWhiteSpace();
+
+	while (parser.currentCharacter() != ')')
+	{
+		eitherType->m_allowedTypes.push_back(&PrimitiveType::parse(parser, context));
+
+		parser.skipWhiteSpace();
+	}
+
+	context.eitherTypes.emplace_back(std::move(eitherType));
+
+	parser.expect<std::string>(")");
+
+	return *context.eitherTypes.back();
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+const std::vector<const PrimitiveType *> &EitherType::allowedTypes() const
+{
+	return m_allowedTypes;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+}
+}
diff --git a/src/plasp/pddl/Predicate.cpp b/src/plasp/pddl/Predicate.cpp
index 7372fc6..507a10b 100644
--- a/src/plasp/pddl/Predicate.cpp
+++ b/src/plasp/pddl/Predicate.cpp
@@ -30,17 +30,17 @@ Predicate &Predicate::parseDeclaration(utils::Parser &parser, Context &context)
 
 	const auto predicateName = parser.parseIdentifier(isIdentifier);
 
-	Predicate predicate(predicateName);
+	auto predicate = std::make_unique<Predicate>(Predicate(predicateName));
 
 	// Flag predicate as correctly declared in the types section
-	predicate.setDeclared();
+	predicate->setDeclared();
 
 	parser.skipWhiteSpace();
 
 	// Parse arguments
 	while (parser.currentCharacter() != ')')
 	{
-		predicate.m_arguments.emplace_back(Variable::parse(parser, context));
+		predicate->m_arguments.emplace_back(Variable::parse(parser, context));
 
 		parser.skipWhiteSpace();
 
@@ -48,11 +48,22 @@ Predicate &Predicate::parseDeclaration(utils::Parser &parser, Context &context)
 		if (!parser.advanceIf('-'))
 			continue;
 
+		auto parseType =
+			[&]() -> TypePtr
+			{
+				parser.skipWhiteSpace();
+
+				if (parser.currentCharacter() == '(')
+					return TypePtr(&EitherType::parse(parser, context));
+
+				return TypePtr(&PrimitiveType::parse(parser, context));
+			};
+
 		// Parse argument type
-		const auto &type = TypePrimitive::parse(parser, context);
+		const auto type = parseType();
 
 		// Set the argument type for all previously flagged arguments
-		std::for_each(predicate.m_arguments.begin(), predicate.m_arguments.end(),
+		std::for_each(predicate->m_arguments.begin(), predicate->m_arguments.end(),
 			[&](auto &argument)
 			{
 				if (!argument.isDirty())
@@ -67,14 +78,16 @@ Predicate &Predicate::parseDeclaration(utils::Parser &parser, Context &context)
 
 	parser.expect<std::string>(")");
 
-	const auto predicateArity = predicate.m_arguments.size();
+	const auto predicateArity = predicate->m_arguments.size();
 	const PredicateHashMapKey key = {predicateName, predicateArity};
 
-	const auto insertionResult = context.predicates.emplace(std::make_pair(key, std::move(predicate)));
+	// Store new predicate
+	context.predicates.emplace_back(std::move(predicate));
 
-	std::cout << "Emplaced " << insertionResult.first->second.name() << std::endl;
+	// Add a pointer to the predicate to the hash map
+	context.predicatesHashMap.emplace(std::make_pair(key, context.predicates.back().get()));
 
-	return insertionResult.first->second;
+	return *context.predicates.back();
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/src/plasp/pddl/PrimitiveType.h b/src/plasp/pddl/PrimitiveType.cpp
similarity index 65%
rename from src/plasp/pddl/PrimitiveType.h
rename to src/plasp/pddl/PrimitiveType.cpp
index 9f25166..f922d3a 100644
--- a/src/plasp/pddl/PrimitiveType.h
+++ b/src/plasp/pddl/PrimitiveType.cpp
@@ -1,4 +1,4 @@
-#include <plasp/pddl/TypePrimitive.h>
+#include <plasp/pddl/PrimitiveType.h>
 
 #include <algorithm>
 
@@ -12,11 +12,11 @@ namespace pddl
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 //
-// TypePrimitive
+// PrimitiveType
 //
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-TypePrimitive::TypePrimitive(std::string name)
+PrimitiveType::PrimitiveType(std::string name)
 :	m_isDirty{false},
 	m_isDeclared{false},
 	m_name(name)
@@ -25,37 +25,41 @@ TypePrimitive::TypePrimitive(std::string name)
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-TypePrimitive &TypePrimitive::parse(utils::Parser &parser, Context &context)
+PrimitiveType &PrimitiveType::parse(utils::Parser &parser, Context &context)
 {
 	parser.skipWhiteSpace();
 
 	const auto typeName = parser.parseIdentifier(isIdentifier);
-	const auto match = context.types.find(typeName);
-	const auto typeExists = (match != context.types.cend());
+	const auto match = context.primitiveTypesHashMap.find(typeName);
+	const auto typeExists = (match != context.primitiveTypesHashMap.cend());
 
+	// Return existing primitive types
 	if (typeExists)
 	{
-		auto &type = match->second;
-		auto &primitiveType = boost::get<TypePrimitive>(type);
+		auto &type = *match->second;
 
-		primitiveType.setDirty();
+		type.setDirty();
 
-		return primitiveType;
+		return type;
 	}
 
-	const auto insertionResult = context.types.emplace(std::make_pair(typeName, TypePrimitive(typeName)));
-	auto &type = insertionResult.first->second;
-	auto &primitiveType = boost::get<TypePrimitive>(type);
+	// Store new primitive type
+	context.primitiveTypes.emplace_back(std::make_unique<PrimitiveType>(PrimitiveType(typeName)));
+
+	auto &type = *context.primitiveTypes.back();
+
+	// Add a pointer to the primitive type to the hash map
+	context.primitiveTypesHashMap.emplace(std::make_pair(typeName, &type));
 
 	// Flag type for potentially upcoming parent type declaration
-	primitiveType.setDirty();
+	type.setDirty();
 
-	return primitiveType;
+	return type;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-TypePrimitive &TypePrimitive::parseDeclaration(utils::Parser &parser, Context &context)
+PrimitiveType &PrimitiveType::parseDeclaration(utils::Parser &parser, Context &context)
 {
 	// Parse and store type
 	auto &type = parse(parser, context);
@@ -79,16 +83,14 @@ TypePrimitive &TypePrimitive::parseDeclaration(utils::Parser &parser, Context &c
 		parentType.setDeclared();
 
 	// Assign parent type to all types that were previously flagged
-	std::for_each(context.types.begin(), context.types.end(),
+	std::for_each(context.primitiveTypes.begin(), context.primitiveTypes.end(),
 		[&](auto &childType)
 		{
-			auto &childTypePrimitive = boost::get<TypePrimitive>(childType.second);
-
-			if (!childTypePrimitive.isDirty())
+			if (!childType->isDirty())
 				return;
 
-			childTypePrimitive.addParentType(parentType);
-			childTypePrimitive.setDirty(false);
+			childType->addParentType(parentType);
+			childType->setDirty(false);
 		});
 
 	return type;
@@ -96,49 +98,49 @@ TypePrimitive &TypePrimitive::parseDeclaration(utils::Parser &parser, Context &c
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void TypePrimitive::setDirty(bool isDirty)
+void PrimitiveType::setDirty(bool isDirty)
 {
 	m_isDirty = isDirty;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-bool TypePrimitive::isDirty() const
+bool PrimitiveType::isDirty() const
 {
 	return m_isDirty;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void TypePrimitive::setDeclared()
+void PrimitiveType::setDeclared()
 {
 	m_isDeclared = true;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-bool TypePrimitive::isDeclared() const
+bool PrimitiveType::isDeclared() const
 {
 	return m_isDeclared;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-const std::string &TypePrimitive::name() const
+const std::string &PrimitiveType::name() const
 {
 	return m_name;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void TypePrimitive::addParentType(const TypePrimitive &parentType)
+void PrimitiveType::addParentType(const PrimitiveType &parentType)
 {
 	m_parentTypes.emplace_back(&parentType);
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-const std::vector<const TypePrimitive *> &TypePrimitive::parentTypes() const
+const std::vector<const PrimitiveType *> &PrimitiveType::parentTypes() const
 {
 	return m_parentTypes;
 }
diff --git a/src/plasp/pddl/Variable.cpp b/src/plasp/pddl/Variable.cpp
index af566df..d916b06 100644
--- a/src/plasp/pddl/Variable.cpp
+++ b/src/plasp/pddl/Variable.cpp
@@ -61,18 +61,16 @@ const std::string &Variable::name() const
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-void Variable::setType(const Type &type)
+void Variable::setType(TypePtr type)
 {
-	m_type = &type;
+	m_type = type;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-const Type &Variable::type() const
+TypePtr Variable::type() const
 {
-	BOOST_ASSERT(m_type != nullptr);
-
-	return *m_type;
+	return m_type;
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
diff --git a/tests/TestPDDLParser.cpp b/tests/TestPDDLParser.cpp
index 554719b..8d6ced2 100644
--- a/tests/TestPDDLParser.cpp
+++ b/tests/TestPDDLParser.cpp
@@ -48,22 +48,40 @@ TEST_F(PDDLParserTests, ParseBlocksWorldDomain)
 
 		const auto &domain = description.domain();
 
+		// Name
 		ASSERT_EQ(domain.name(), "BLOCKS");
 
+		// Requirements
 		ASSERT_EQ(domain.requirements().size(), 2u);
 		ASSERT_EQ(domain.requirements()[0].type(), plasp::pddl::Requirement::Type::STRIPS);
 		ASSERT_EQ(domain.requirements()[1].type(), plasp::pddl::Requirement::Type::Typing);
 
+		// Types
 		ASSERT_EQ(domain.types().size(), 1u);
 
-		const auto block = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("block")->second);
+		const auto &block = *domain.types()[0];
 
 		ASSERT_EQ(block.name(), "block");
 		ASSERT_EQ(block.parentTypes().size(), 0u);
 
+		// Predicates
 		ASSERT_EQ(domain.predicates().size(), 5u);
 
-		const auto on = domain.predicates().find({"on", 2});
+		const auto &on = *domain.predicates()[0];
+
+		ASSERT_EQ(on.name(), "on");
+		ASSERT_EQ(on.arguments().size(), 2u);
+		ASSERT_EQ(on.arguments()[0].name(), "x");
+		const auto onArgument0Type = boost::get<const plasp::pddl::PrimitiveType *>(on.arguments()[0].type());
+		ASSERT_EQ(onArgument0Type, &block);
+		ASSERT_EQ(on.arguments()[1].name(), "y");
+		const auto onArgument1Type = boost::get<const plasp::pddl::PrimitiveType *>(on.arguments()[1].type());
+		ASSERT_EQ(onArgument1Type, &block);
+
+		const auto &handempty = *domain.predicates()[3];
+
+		ASSERT_EQ(handempty.name(), "handempty");
+		ASSERT_TRUE(handempty.arguments().empty());
 	}
 	catch (const std::exception &e)
 	{
@@ -83,16 +101,22 @@ TEST_F(PDDLParserTests, ParseStorageDomain)
 
 		const auto &domain = description.domain();
 
+		// Name
 		ASSERT_EQ(domain.name(), "Storage-Propositional");
 
+		// Requirements
 		ASSERT_EQ(domain.requirements().size(), 1u);
 		ASSERT_EQ(domain.requirements()[0].type(), plasp::pddl::Requirement::Type::Typing);
 
-		const auto area = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("area")->second);
-		const auto hoist = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("hoist")->second);
-		const auto object = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("object")->second);
-		const auto storearea = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("storearea")->second);
-		const auto surface = boost::get<plasp::pddl::TypePrimitive>(domain.types().find("surface")->second);
+		// Types
+		ASSERT_EQ(domain.types().size(), 10u);
+
+		const auto &hoist = *domain.types()[0];
+		const auto &surface = *domain.types()[1];
+		const auto &area = *domain.types()[3];
+		const auto &object = *domain.types()[4];
+		const auto &storearea = *domain.types()[7];
+		const auto &crate = *domain.types()[9];
 
 		const auto &hoistParents = hoist.parentTypes();
 		ASSERT_EQ(hoistParents.size(), 1u);
@@ -102,6 +126,29 @@ TEST_F(PDDLParserTests, ParseStorageDomain)
 		ASSERT_EQ(areaParents.size(), 2u);
 		ASSERT_TRUE(std::find(areaParents.cbegin(), areaParents.cend(), &object) != areaParents.cend());
 		ASSERT_TRUE(std::find(areaParents.cbegin(), areaParents.cend(), &surface) != areaParents.cend());
+
+		// Predicates
+		ASSERT_EQ(domain.predicates().size(), 8u);
+
+		const auto &on = *domain.predicates()[5];
+
+		ASSERT_EQ(on.name(), "on");
+		ASSERT_EQ(on.arguments().size(), 2u);
+		ASSERT_EQ(on.arguments()[0].name(), "c");
+		const auto onArgument0Type = boost::get<const plasp::pddl::PrimitiveType *>(on.arguments()[0].type());
+		ASSERT_EQ(onArgument0Type, &crate);
+		ASSERT_EQ(on.arguments()[1].name(), "s");
+		const auto onArgument1Type = boost::get<const plasp::pddl::PrimitiveType *>(on.arguments()[1].type());
+		ASSERT_EQ(onArgument1Type, &storearea);
+
+		const auto &in = *domain.predicates()[1];
+		ASSERT_EQ(in.name(), "in");
+		ASSERT_EQ(in.arguments().size(), 2u);
+		ASSERT_EQ(in.arguments()[0].name(), "x");
+		const auto inArgument0Type = boost::get<const plasp::pddl::EitherType *>(in.arguments()[0].type());
+		ASSERT_EQ(inArgument0Type->allowedTypes().size(), 2u);
+		ASSERT_EQ(inArgument0Type->allowedTypes()[0], &storearea);
+		ASSERT_EQ(inArgument0Type->allowedTypes()[1], &crate);
 	}
 	catch (const std::exception &e)
 	{
diff --git a/tests/data/storage-domain.pddl b/tests/data/storage-domain.pddl
index c001130..911b159 100644
--- a/tests/data/storage-domain.pddl
+++ b/tests/data/storage-domain.pddl
@@ -1,32 +1,32 @@
 (define (domain Storage-Propositional)
 (:requirements :typing)
 (:types hoist surface place area - object
-	container depot - place
-	storearea transitarea - area
-	area crate - surface)
+    container depot - place
+    storearea transitarea - area
+    area crate - surface)
 
 (:predicates (clear ?s - storearea)
-	     (in ?x - (either storearea crate) ?p - place)
-	     (available ?h - hoist) 
-	     (lifting ?h - hoist ?c - crate) 
-	     (at ?h - hoist ?a - area)
-	     (on ?c - crate ?s - storearea) 
-	     (connected ?a1 ?a2 - area)
+         (in ?x - (either storearea crate) ?p - place)
+         (available ?h - hoist) 
+         (lifting ?h - hoist ?c - crate) 
+         (at ?h - hoist ?a - area)
+         (on ?c - crate ?s - storearea) 
+         (connected ?a1 ?a2 - area)
              (compatible ?c1 ?c2 - crate)) 
 
 (:action lift
  :parameters (?h - hoist ?c - crate ?a1 - storearea ?a2 - area ?p - place)
  :precondition (and (connected ?a1 ?a2) (at ?h ?a2) (available ?h) 
-		    (on ?c ?a1) (in ?a1 ?p))
+            (on ?c ?a1) (in ?a1 ?p))
  :effect (and (not (on ?c ?a1)) (clear ?a1)
-	      (not (available ?h)) (lifting ?h ?c) (not (in ?c ?p))))
-				
+          (not (available ?h)) (lifting ?h ?c) (not (in ?c ?p))))
+                
 (:action drop
  :parameters (?h - hoist ?c - crate ?a1 - storearea ?a2 - area ?p - place)
  :precondition (and (connected ?a1 ?a2) (at ?h ?a2) (lifting ?h ?c) 
-		    (clear ?a1) (in ?a1 ?p))
+            (clear ?a1) (in ?a1 ?p))
  :effect (and (not (lifting ?h ?c)) (available ?h)
-	      (not (clear ?a1)) (on ?c ?a1) (in ?c ?p)))
+          (not (clear ?a1)) (on ?c ?a1) (in ?c ?p)))
 
 (:action move
  :parameters (?h - hoist ?from ?to - storearea)