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diff --git a/include/sdl/errorqueries.hpp b/include/sdl/errorqueries.hpp
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+/*
+   Copyright (c) 2018-2019 Nokia.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+/** @file */
+
+#ifndef SHAREDDATALAYER_ERRORQUERIES_HPP_
+#define SHAREDDATALAYER_ERRORQUERIES_HPP_
+
+#include <system_error>
+
+namespace shareddatalayer
+{
+   /** @enum shareddatalayer::Error
+     * @brief Error constants meant for client error handling implementation.
+     *
+     * Certain <code>std::error_code</code>s returned by shareddatalayer can
+     * be compared against these enum values. If returned error can be compared
+     * against these values, it is mentioned in the documentation of the
+     * functionality which returns the <code>std::error_code</code>.
+     *
+     * Descriptions of the <code>shareddatalayer::Error</code> values and
+     * instructions how to handle each value:
+     *
+     * <code>shareddatalayer::Error::SUCCESS</code>:<br>
+     * Request was successfully handled, no error handling needed.
+     *
+     * <code>shareddatalayer::Error::NOT_CONNECTED</code>:<br>
+     * shareddatalayer is not connected to the backend data storage and therefore could not
+     * deliver the request to the backend data storage. Data in the backend data storage
+     * has not been altered.<br>
+     * Client is advised to try the operation again later. If shareddatalayer class,
+     * from which the error originated, contains <code>waitReadyAsync</code> API, client
+     * can use <code>waitReadyAsync</code> API to get a notification once shareddatalayer
+     * is connected to the backend data storage.<br>
+     * Note that if client receives this error for the first SDL API operation which client does,
+     * it is advised to modify client implementation so that client waits for <code>waitReadyAsync</code>
+     * notification before doing any SDL API operations.
+     *
+     * <code>shareddatalayer::Error::OPERATION_INTERRUPTED</code>:<br>
+     * shareddatalayer sent the request to the backend data storage but did not receive a reply from
+     * the backend data storage. In case of a write type request, data in the backend data storage
+     * may or may not have been altered.<br>
+     * Client is advised to try the operation again later. If shareddatalayer class, from which the error originated,
+     * contains waitReadyAsync API, client can use waitReadyAsync API to get a notification once shareddatalayer is
+     * connected to the backend data storage.<br>
+     * When shareddatalayer operations work again, client can choose how to best address the possible loss of consistency.
+     * Client can re-do all the interrupted writes or read the current data in the backend data storage and update it accordingly.
+     *
+     * <code>shareddatalayer::Error::BACKEND_FAILURE</code>:<br>
+     * shareddatalayer delivered the request to the backend data storage but the backend data storage failed to process the request.
+     * In case of a write type request, data in the backend data storage may or may not have been altered.<br>
+     * Client is advised to try the operation again later. Optionally client can also re-create the used shareddatalayer instance.
+     * It is possible that the system does not automatically recover from this type of error situations. Therefore client is advised
+     * to escalate the problem to O&M if operation does not succeed after several retries.<br>
+     * When shareddatalayer operations work again, client can choose how to best address the possible loss of consistency
+     * (see <code>shareddatalayer::Error::OPERATION_INTERRUPTED</code> for possible options).
+     *
+     * <code>shareddatalayer::Error::REJECTED_BY_BACKEND</code>:<br>
+     * shareddatalayer delivered the request to the backend data storage but the backend data storage rejected the request.
+     * In case of a write type request, data in the backend data storage may or may not have been altered.<br>
+     * It is likely that same request will fail repeatedly. It is advised to investigate the exact reason for the failure from the logs.
+     * Reason can be, for example, too many keys in the request or too large data in the request. It is backend specific, what kind of
+     * request is considered invalid. Redis is the most common backend type, maximum supported request parameters with Redis backend
+     * are currently by default following:
+     * maximum amount of keys in request: 524287 keys, maximum key/value size: 512MB.
+     * If the client request is invalid, client implementation needs to be changed. If the reason for invalid request seems to originate
+     * from shareddatalayer, contact shareddatalayer support. <br>
+     * When shareddatalayer operations work again, client can choose how to best address the possible loss of consistency
+     * (see <code>shareddatalayer::Error::OPERATION_INTERRUPTED</code> for possible options).
+     *
+     * <code>shareddatalayer::Error::REJECTED_BY_SDL</code>:<br>
+     * shareddatalayer could not process the request and therefore did not deliver the request to the backend data storage.
+     * Data in the backend data storage has not been altered.<br>
+     * It is likely that same request will fail repeatedly. Reason can be, for example, illegal parameter passed to SDL API function.
+     * It is advised to investigate the exact reason for the failure, for example, by investigating logs and returned <code>std::error_code</code>.
+     * If the client request is invalid, client implementation needs to be changed.<br>
+     */
+    enum class Error
+    {
+        SUCCESS = 0,
+        NOT_CONNECTED,
+        OPERATION_INTERRUPTED,
+        BACKEND_FAILURE,
+        REJECTED_BY_BACKEND,
+        REJECTED_BY_SDL
+    };
+
+    /// @private
+    std::error_condition make_error_condition(shareddatalayer::Error ec);
+}
+
+namespace std
+{
+    /// @private
+    template <>
+    struct is_error_condition_enum<shareddatalayer::Error> : public true_type { };
+}
+
+#endif