diff --git a/src/data_query.hpp b/src/data_query.hpp
new file mode 100644
index 0000000..b2f4a33
--- /dev/null
+++ b/src/data_query.hpp
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2019 CESNET, https://photonics.cesnet.cz/
+ *
+ * Written by Václav Kubernát <kubernat@cesnet.cz>
+ *
+*/
+
+#pragma once
+
+#include <boost/optional.hpp>
+#include <map>
+#include <memory>
+#include <set>
+#include "ast_values.hpp"
+#include "datastore_access.hpp"
+#include "schema.hpp"
+
+
+/*! \class DataQuery
+ *  \brief A class used for querying data from a datastore for usage in tab-completion.
+ *
+*/
+class DataQuery {
+public:
+    DataQuery(DatastoreAccess& datastore);
+    /*! \brief Lists all possible instances of key/value pairs for a list specified by the arguments.
+     *  \param location Location of the list.
+     *  \param node Name (and optional module name) of the list.
+     *  \return A vector of maps, which represent the instances. The map is keyed by the name of the list key. The values in the map, are values of the list keys.
+     */
+    std::vector<ListInstance> listKeys(const dataPath_& location, const ModuleNodePair& node) const;
+
+private:
+    DatastoreAccess& m_datastore;
+    std::shared_ptr<Schema> m_schema;
+};