diff --git a/include/opcbase.idl b/include/opcbase.idl
index fc926754203..33f56ac077a 100644
--- a/include/opcbase.idl
+++ b/include/opcbase.idl
@@ -25,3 +25,18 @@ typedef [v1_enum] enum
     OPC_STREAM_IO_READ = 1,
     OPC_STREAM_IO_WRITE = 2,
 } OPC_STREAM_IO_MODE;
+
+typedef [v1_enum] enum
+{
+    OPC_COMPRESSION_NONE = -1,
+    OPC_COMPRESSION_NORMAL = 0,
+    OPC_COMPRESSION_MAXIMUM = 1,
+    OPC_COMPRESSION_FAST = 2,
+    OPC_COMPRESSION_SUPERFAST = 3,
+} OPC_COMPRESSION_OPTIONS;
+
+typedef [v1_enum] enum
+{
+    OPC_URI_TARGET_MODE_INTERNAL = 0,
+    OPC_URI_TARGET_MODE_EXTERNAL = 1,
+} OPC_URI_TARGET_MODE;
diff --git a/include/opcobjectmodel.idl b/include/opcobjectmodel.idl
index e5370d2e545..45bc8aa4a58 100644
--- a/include/opcobjectmodel.idl
+++ b/include/opcobjectmodel.idl
@@ -20,6 +20,11 @@
 #pragma makedep install
 #endif
 
+interface IOpcPart;
+interface IOpcPartUri;
+interface IOpcUri;
+interface IOpcRelationship;
+
 typedef [v1_enum] enum
 {
     OPC_READ_DEFAULT = 0,
@@ -32,3 +37,172 @@ typedef [v1_enum] enum
     OPC_WRITE_DEFAULT = 0,
     OPC_WRITE_FORCE_ZIP32 = 1,
 } OPC_WRITE_FLAGS;
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee75),
+    pointer_default(ref)
+]
+interface IOpcPartEnumerator : IUnknown
+{
+    HRESULT MoveNext(
+        [out, retval] BOOL *has_next
+    );
+
+    HRESULT MovePrevious(
+        [out, retval] BOOL *has_previous
+    );
+
+    HRESULT GetCurrent(
+        [out, retval] IOpcPart **part
+    );
+
+    HRESULT Clone(
+        [out, retval] IOpcPartEnumerator **enumerator
+    );
+}
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee76),
+    pointer_default(ref)
+]
+interface IOpcRelationshipEnumerator : IUnknown
+{
+    HRESULT MoveNext(
+        [out, retval] BOOL *has_next
+    );
+
+    HRESULT MovePrevious(
+        [out, retval] BOOL *has_previous
+    );
+
+    HRESULT GetCurrent(
+        [out, retval] IOpcRelationship **relationship
+    );
+
+    HRESULT Clone(
+        [out, retval] IOpcRelationshipEnumerator **enumerator
+    );
+}
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee73),
+    pointer_default(ref)
+]
+interface IOpcPartSet : IUnknown
+{
+    HRESULT GetPart(
+        [in] IOpcPartUri *name,
+        [out, retval] IOpcPart **part
+    );
+
+    HRESULT CreatePart(
+        [in] IOpcPartUri *name,
+        [in, string] LPCWSTR content_type,
+        [in] OPC_COMPRESSION_OPTIONS compression_options,
+        [out, retval] IOpcPart **part
+    );
+
+    HRESULT DeletePart(
+        [in] IOpcPartUri *name
+    );
+
+    HRESULT PartExists(
+        [in] IOpcPartUri *name,
+        [out, retval] BOOL *exists
+    );
+
+    HRESULT GetEnumerator(
+        [out, retval] IOpcPartEnumerator **enumerator
+    );
+}
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee72),
+    pointer_default(ref)
+]
+interface IOpcRelationship : IUnknown
+{
+    HRESULT GetId(
+        [out, string, retval] LPWSTR *id
+    );
+
+    HRESULT GetRelationshipType(
+        [out, string, retval] LPWSTR *type
+    );
+
+    HRESULT GetSourceUri(
+        [out, retval] IOpcUri **uri
+    );
+
+    HRESULT GetTargetUri(
+        [out, retval] IUri **target
+    );
+
+    HRESULT GetTargetMode(
+        [out, retval] OPC_URI_TARGET_MODE *target_mode
+    );
+}
+
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee74),
+    pointer_default(ref)
+]
+interface IOpcRelationshipSet : IUnknown
+{
+    HRESULT GetRelationship(
+        [in, string] LPCWSTR id,
+        [out, retval] IOpcRelationship **relationship
+    );
+
+    HRESULT CreateRelationship(
+        [in, string, unique] LPCWSTR id,
+        [in, string] LPCWSTR type,
+        [in] IUri *target_uri,
+        [in] OPC_URI_TARGET_MODE target_mode,
+        [out, retval] IOpcRelationship **relationship
+    );
+
+    HRESULT DeleteRelationship(
+        [in, string] LPCWSTR id
+    );
+
+    HRESULT RelationshipExists(
+        [in, string] LPCWSTR id,
+        [out, retval] BOOL *exists
+    );
+
+    HRESULT GetEnumerator(
+        [out, retval] IOpcRelationshipEnumerator **enumerator
+    );
+
+    HRESULT GetEnumeratorForType(
+        [in, string] LPCWSTR type,
+        [out, retval] IOpcRelationshipEnumerator **enumerator
+    );
+
+    HRESULT GetRelationshipsContentStream(
+        [out, retval] IStream **stream
+    );
+}
+
+[
+    object,
+    uuid(42195949-3b79-4fc8-89c6-fc7fb979ee70),
+    pointer_default(ref)
+]
+interface IOpcPackage : IUnknown
+{
+    HRESULT GetPartSet(
+        [out, retval] IOpcPartSet **part_set
+    );
+
+    HRESULT GetRelationshipSet(
+        [out, retval] IOpcRelationshipSet **relationship_set
+    );
+}