diff --git a/src/pq/pq_common.h b/src/pq/pq_common.h
new file mode 100644
index 000000000..36ba62a40
--- /dev/null
+++ b/src/pq/pq_common.h
@@ -0,0 +1,96 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2023 Taler Systems SA
+
+  TALER 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 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file pq/pq_common.h
+ * @brief common defines for the pq functions
+ * @author Özgür Kesim
+ */
+#ifndef TALER_PQ_COMMON_H_
+#define TALER_PQ_COMMON_H_
+
+#include "platform.h"
+/**
+ * Internal types that are supported as TALER-exchange-specific array types.
+ *
+ * To support a new type,
+ *   1. add a new entry into this list,
+ *   2. for query-support, implement the size calculation and memory copying in
+ *      qconv_array() accordingly, in pq_query_helper.c
+ *   3. provide a query-API for arrays of the type, by calling
+ *      query_param_array_generic with the appropriate parameters,
+ *      in pq_query_helper.c
+ *   4. for result-support, implement memory copying by adding another case
+ *      to extract_array_generic, in pq_result_helper.c
+ *   5. provide a result-spec-API for arrays of the type,
+ *      in pq_result_helper.c
+ *   6. expose the API's in taler_pq_lib.h
+ */
+enum TALER_PQ_ArrayType
+{
+  TALER_PQ_array_of_blinded_denom_sig,
+  TALER_PQ_array_of_blinded_coin_hash,
+  TALER_PQ_array_of_denom_hash,
+  /* TODO[oec]: Next up: TALER_PQ_array_of_amount, */
+  TALER_PQ_array_of_MAX,       /* must be last */
+};
+
+/**
+ * The header for a postgresql array in binary format. note that this a
+ * simplified special case of the general structure (which contains pointers),
+ * as we only support one-dimensional arrays.
+ */
+struct TALER_PQ_ArrayHeader_P
+{
+  uint32_t ndim;     /* number of dimensions. we only support ndim = 1 */
+  uint32_t has_null;
+  uint32_t oid;
+  uint32_t dim;      /* size of the array */
+  uint32_t lbound;   /* index value of first element in the db (default: 1). */
+} __attribute__((packed));
+
+/**
+ * Memory representation of an taler amount record for Postgres.
+ *
+ * All values need to be in network-byte-order.
+ */
+struct TALER_PQ_Amount_P
+{
+  uint32_t oid_v; /* oid of .v  */
+  uint32_t sz_v;  /* size of .v */
+  uint64_t v;     /* value      */
+  uint32_t oid_f; /* oid of .f  */
+  uint32_t sz_f;  /* size of .f */
+  uint32_t f;     /* fraction   */
+} __attribute__((packed));
+
+/**
+ * Create a `struct TALER_PQ_Amount_P` for initialization
+ *
+ * @param db postgres-context of type `struct GNUNET_PQ_Context *`
+ * @param amount amount of type `struct TALER_Amount *`
+ */
+#define MAKE_TALER_PQ_AMOUNT_P(db,amount) \
+  { \
+    .oid_v = htonl (GNUNET_PQ_get_oid ((db), GNUNET_PQ_DATATYPE_INT8)), \
+    .oid_f = htonl (GNUNET_PQ_get_oid ((db), GNUNET_PQ_DATATYPE_INT4)), \
+    .sz_v = htonl (sizeof((amount)->value)), \
+    .sz_f = htonl (sizeof((amount)->fraction)), \
+    .v = GNUNET_htonll ((amount)->value), \
+    .f = htonl ((amount)->fraction) \
+  }
+
+#endif  /* TALER_PQ_COMMON_H_ */
+/* end of pg/pq_common.h */