diff --git a/pisi/relation.py b/pisi/relation.py
new file mode 100644
index 00000000..41aeda5f
--- /dev/null
+++ b/pisi/relation.py
@@ -0,0 +1,75 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2007, TUBITAK/UEKAE
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free
+# Software Foundation; either version 2 of the License, or (at your option)
+# any later version.
+#
+# Please read the COPYING file.
+#
+
+import gettext
+__trans = gettext.translation('pisi', fallback=True)
+_ = __trans.ugettext
+
+import pisi.context as ctx
+import pisi.version
+import pisi.pxml.autoxml as autoxml
+import pisi.itembyrepodb
+
+class Relation:
+
+    __metaclass__ = autoxml.autoxml
+
+    s_Package = [autoxml.String, autoxml.mandatory]
+    a_version = [autoxml.String, autoxml.optional]
+    a_versionFrom = [autoxml.String, autoxml.optional]
+    a_versionTo = [autoxml.String, autoxml.optional]
+    a_release = [autoxml.String, autoxml.optional]
+    a_releaseFrom = [autoxml.String, autoxml.optional]
+    a_releaseTo = [autoxml.String, autoxml.optional]
+
+    def __str__(self):
+        s = self.package
+        if self.versionFrom:
+            s += _(" version >= ") + self.versionFrom
+        if self.versionTo:
+            s += _(" version <= ") + self.versionTo
+        if self.version:
+            s += _(" version ") + self.version
+        if self.releaseFrom:
+            s += _(" release >= ") + self.releaseFrom
+        if self.releaseTo:
+            s += _(" release <= ") + self.releaseTo
+        if self.release:
+            s += _(" release ") + self.release
+        return s
+
+    def satisfies_relation(self, pkg_name, version, release):
+        ret = True
+        v = pisi.version.Version(version)
+        if self.version:
+            ret &= v == pisi.version.Version(self.version)
+        if self.versionFrom:
+            ret &= v >= pisi.version.Version(self.versionFrom)
+        if self.versionTo:
+            ret &= v <= pisi.version.Version(self.versionTo)
+        r = pisi.version.Version(release)
+        if self.release:
+            ret &= r == pisi.version.Version(self.release)
+        if self.releaseFrom:
+            ret &= r >= pisi.version.Version(self.releaseFrom)
+        if self.releaseTo:
+            ret &= r <= pisi.version.Version(self.releaseTo)
+        return ret
+
+def installed_package_satisfies(relation):
+    pkg_name = relation.package
+    if not ctx.installdb.is_installed(pkg_name):
+        return False
+    else:
+        pkg = ctx.packagedb.get_package(pkg_name, pisi.itembyrepodb.installed)
+        (version, release) = (pkg.version, pkg.release)
+        return relation.satisfies_relation(pkg_name, version, release)