diff --git a/trabalho-pratico/include/types/account_status.h b/trabalho-pratico/include/types/account_status.h
new file mode 100644
index 0000000..3428c21
--- /dev/null
+++ b/trabalho-pratico/include/types/account_status.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     account_status.h
+ * @brief    Account status of a ::user_t.
+ */
+
+#ifndef ACCOUNT_STATUS_H
+#define ACCOUNT_STATUS_H
+
+/** @brief The account status of a ::user_t. */
+typedef enum {
+    ACCOUNT_STATUS_INACTIVE, /**< @brief Inactive account */
+    ACCOUNT_STATUS_ACTIVE    /**< @brief Active account */
+} account_status_t;
+
+/**
+ * @brief Parses a user's account status.
+ *
+ * @param output Where the parsed status will be placed (only on success).
+ * @param input  Input (`"active"` or `"inactive"`, case-insensitive).
+ *
+ * @retval 0 Parsing success
+ * @retval 1 Parsing failure
+ */
+int account_status_from_string(account_status_t *output, const char *input);
+
+#endif
diff --git a/trabalho-pratico/include/types/airport_code.h b/trabalho-pratico/include/types/airport_code.h
new file mode 100644
index 0000000..362190e
--- /dev/null
+++ b/trabalho-pratico/include/types/airport_code.h
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     airport_code.h
+ * @brief    Airport code in a ::flight_t.
+ *
+ * @anchor airport_examples
+ * ### Examples
+ *
+ * The following example shows how to validate airport codes and how to print them back to strings.
+ * It's also shown that all airport codes are stored in upper-case.
+ *
+ * ```c
+ * const char *string_codes[6] = {
+ *     "",     // Too short
+ *     "O",    // Too short
+ *     "OP",   // Too short
+ *     "OPO",  // Just right
+ *     "oPo",  // Everything should be converted to upper-case
+ *     "OPOR", // Too long
+ * };
+ *
+ * for (int i = 0; i < 6; ++i) {
+ *     airport_code_t parsed;
+ *
+ *     if (!airport_code_from_string(&parsed, string_codes[i])) {
+ *         char back_to_string[AIRPORT_CODE_SPRINTF_MIN_BUFFER_SIZE];
+ *         airport_code_sprintf(back_to_string, parsed);
+ *         printf("Parsed code: \"%s\"\n", back_to_string);
+ *
+ *     } else {
+ *         fprintf(stderr, "Failed to parse airport code \"%s\"!\n", string_codes[i]);
+ *     }
+ * }
+ * ```
+ */
+
+#ifndef AIRPORT_CODE_H
+#define AIRPORT_CODE_H
+
+#include <stdint.h>
+
+/**
+ * @brief An airport code of a ::flight_t.
+ */
+typedef uint32_t airport_code_t;
+
+/**
+ * @brief Creates (and validates) a airport code from a string.
+ *
+ * @param output Where to place the parsed airport code (not modified on failure).
+ * @param input  String to parse.
+ *
+ * @retval 0 Valid airport code
+ * @retval 1 Invalid airport code
+ */
+int airport_code_from_string(airport_code_t *output, const char *input);
+
+/**
+ * @brief The minimum number of characters (including null terminator) needed to write an airport
+ *        code to a buffer using ::airport_code_sprintf.
+ * @details
+ *
+ * | O | P | O | \0 |
+ * | - | - | - | -- |
+ * | 1 | 2 | 3 | 4  |
+ */
+#define AIRPORT_CODE_SPRINTF_MIN_BUFFER_SIZE 4
+
+/**
+ * @brief Prints a airport code using `sprintf`.
+ *
+ * @param output  Where to print the airport code to. Must be at least
+ *                ::AIRPORT_CODE_SPRINTF_MIN_BUFFER_SIZE long.
+ * @param airport Country code to be printed.
+ */
+void airport_code_sprintf(char *output, airport_code_t airport);
+
+#endif
diff --git a/trabalho-pratico/include/types/country_code.h b/trabalho-pratico/include/types/country_code.h
new file mode 100644
index 0000000..3d3a07f
--- /dev/null
+++ b/trabalho-pratico/include/types/country_code.h
@@ -0,0 +1,97 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     country_code.h
+ * @brief    Country code in a ::user_t.
+ *
+ * @anchor country_code_examples
+ * ### Examples
+ *
+ * The following example shows how to validate country codes and how to print them back to strings.
+ *
+ * ```c
+ * const char *string_codes[4] = {
+ *     "",    // Too short
+ *     "P",   // Too short
+ *     "PT",  // Just right
+ *     "POR", // Too long
+ * };
+ *
+ * for (int i = 0; i < 4; ++i) {
+ *     country_code_t parsed;
+ *
+ *     if (!country_code_from_string(&parsed, string_codes[i])) {
+ *         char back_to_string[COUNTRY_CODE_SPRINTF_MIN_BUFFER_SIZE];
+ *         country_code_sprintf(back_to_string, parsed);
+ *         printf("Parsed code: \"%s\"\n", back_to_string);
+ *
+ *     } else {
+ *         fprintf(stderr, "Failed to parse country code \"%s\"!\n", string_codes[i]);
+ *     }
+ * }
+ * ```
+ */
+
+#ifndef COUNTRY_CODE_H
+#define COUNTRY_CODE_H
+
+#include <stdint.h>
+
+/**
+ * @brief A country code of a ::user_t.
+ */
+typedef uint16_t country_code_t;
+
+/**
+ * @brief Creates (and validates) a country code from a string.
+ *
+ * @param output Where to place the parsed country code (not modified on failure).
+ * @param input  String to parse.
+ *
+ * @retval 0 Valid country code
+ * @retval 1 Invalid country code
+ *
+ *
+ * #### Examples
+ * See [the header file's documentation](@ref country_code_examples).
+ */
+int country_code_from_string(country_code_t *output, const char *input);
+
+/**
+ * @brief The minimum number of characters (including null terminator) needed to write a country
+ *        code to a buffer using ::country_code_sprintf.
+ * @details
+ *
+ * | P | T | \0 |
+ * | - | - | -- |
+ * | 1 | 2 | 3  |
+ */
+#define COUNTRY_CODE_SPRINTF_MIN_BUFFER_SIZE 3
+
+/**
+ * @brief Prints a country code using `sprintf`.
+ *
+ * @param output  Where to print the country code to. Must be at least
+ *                ::COUNTRY_CODE_SPRINTF_MIN_BUFFER_SIZE long.
+ * @param country Country code to be printed.
+ *
+ * #### Examples
+ * See [the header file's documentation](@ref country_code_examples).
+ */
+void country_code_sprintf(char *output, country_code_t country);
+
+#endif
diff --git a/trabalho-pratico/include/types/flight.h b/trabalho-pratico/include/types/flight.h
new file mode 100644
index 0000000..c9e5ced
--- /dev/null
+++ b/trabalho-pratico/include/types/flight.h
@@ -0,0 +1,210 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     flight.h
+ * @brief    Declaration of type ::flight_t.
+ *
+ * @details  In this module you can find a declaration of the type `flight_t` as a struct flight,
+ *           as well as getter and setter functions, which allow's the developer access to any
+ *           previously created flight, or gives them the ability to create a new flight.
+ *
+ *           You can see what fields define a flight (and thus available through getters and
+ *           setters) in the [struct's documentation](@ref flight).
+ */
+
+#ifndef FLIGHT_H
+#define FLIGHT_H
+
+#include "types/airport_code.h"
+#include "utils/date_and_time.h"
+
+/**
+ * @brief Type `flight_t` defined as a struct flight, that stores valuable information of a given
+ * flight.
+ * @details It's an opaque type.
+ */
+typedef struct flight flight_t;
+
+/**
+ * @brief Creates a new flight with uninitialized fields.
+ * @return A `malloc`-allocated flight (`NULL` on allocation failure).
+ */
+flight_t *flight_create(void);
+
+/**
+ * @brief Sets the flight's airline.
+ * @details @p airline will not get owned by @p flight, and you should free it later.
+ *
+ * @param flight  Flight to have its airline set.
+ * @param airline Airline of the flight.
+ */
+void flight_set_airline(flight_t *flight, char *airline);
+
+/**
+ * @brief Sets the flight's plane model.
+ * @details @p plane_model will not get owned by @p flight, and you should free it later.
+ *
+ * @param flight      Flight to have its plane model set.
+ * @param plane_model Plane model of the flight.
+ */
+void flight_set_plane_model(flight_t *flight, char *plane_model);
+
+/**
+ * @brief Sets the flight's origin.
+ * @details @p origin will not get owned by @p flight, and you should free it later.
+ *
+ * @param flight Flight to have its origin set.
+ * @param origin Origin of the flight.
+ */
+void flight_set_origin(flight_t *flight, airport_code_t origin);
+
+/**
+ * @brief Sets the flight's destination.
+ * @details @p destination will not get owned by @p flight, and you should free it later.
+ *
+ * @param flight      Flight to have its destination set.
+ * @param destination Destination of the flight.
+ */
+void flight_set_destination(flight_t *flight, airport_code_t destination);
+
+/**
+ * @brief Sets the flight's identifier.
+ * @param flight Flight to have its id set.
+ * @param id     Identifier of the flight.
+ */
+void flight_set_id(flight_t *flight, size_t id);
+
+/**
+ * @brief Sets the flight's scheduled departure date.
+ * @param flight                  Flight to have its scheduled departure date set.
+ * @param schedule_departure_date Scheduled departure date of the flight.
+ */
+void flight_set_schedule_departure_date(flight_t *flight, date_and_time_t schedule_departure_date);
+
+/**
+ * @brief Sets the flight's scheduled arrival date.
+ * @param flight                Flight to have its scheduled arrival date set.
+ * @param schedule_arrival_date Scheduled arrival date of the flight.
+ */
+void flight_set_schedule_arrival_date(flight_t *flight, date_and_time_t schedule_arrival_date);
+
+/**
+ * @brief Increments the flight's number of passengers.
+ * @param flight           Flight to have its number of passengers incremented.
+ * @param increment_factor Factor by which the number of passengers is incremented.
+ */
+void flight_increment_number_of_passengers(flight_t *flight, int increment_factor);
+
+/**
+ * @brief Sets the flight's number of passengers.
+ * @param flight               Flight to have its number of passengers set.
+ * @param number_of_passengers Number of passengers of the flight.
+ */
+void flight_set_number_of_passengers(flight_t *flight, int number_of_passengers);
+
+/**
+ * @brief Sets the flight's real departure date.
+ * @param flight              Flight to have its real departure date set.
+ * @param real_departure_date Real departure date of the flight.
+ */
+void flight_set_real_departure_date(flight_t *flight, date_and_time_t real_departure_date);
+
+/**
+ * @brief Sets the flight's number of total seats.
+ * @param flight      Flight to have its number of total seats set.
+ * @param total_seats Number of total seats of the flight.
+ */
+void flight_set_total_seats(flight_t *flight, int total_seats);
+
+/**
+ * @brief  Gets the flight's airline.
+ * @param  flight Flight to get the airline from.
+ * @return The flight's airline, with modifications not allowed.
+ */
+const char *flight_get_const_airline(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's plane model.
+ * @param  flight Flight to get the plane model from.
+ * @return The flight's plane model, with modifications not allowed.
+ */
+const char *flight_get_const_plane_model(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's origin.
+ * @param  flight Flight to get the origin from.
+ * @return The flight's origin.
+ */
+airport_code_t flight_get_origin(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's destination.
+ * @param  flight Flight to get the destination from.
+ * @return The flight's destination.
+ */
+airport_code_t flight_get_destination(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's identifier.
+ * @param  flight Flight to get the id from.
+ * @return The flight's identifier.
+ */
+size_t flight_get_id(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's scheduled departure date.
+ * @param  flight Flight to get the scheduled departure date from.
+ * @return The flight's scheduled departure date.
+ */
+date_and_time_t flight_get_schedule_departure_date(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's scheduled arrival date.
+ * @param  flight Flight to get the scheduled arrival date from.
+ * @return The flight's scheduled arrival date.
+ */
+date_and_time_t flight_get_schedule_arrival_date(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's number of passengers.
+ * @param  flight Flight to get the number of passengers from.
+ * @return The flight's number of passengers.
+ */
+int flight_get_number_of_passengers(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's real departure date.
+ * @param  flight Flight to get the real departure date from.
+ * @return The flight's departure date.
+ */
+date_and_time_t flight_get_real_departure_date(const flight_t *flight);
+
+/**
+ * @brief  Gets the flight's number of total seats.
+ * @param  flight Flight to get the number of total seats from.
+ * @return The flight's number of total seats.
+ */
+int flight_get_total_seats(const flight_t *flight);
+
+/**
+ * @brief        Frees the memory used for a given flight.
+ * @details      All strings inside the flight won't be freed, as they're not owned by the flight.
+ * @param flight FLight to be deleted.
+ */
+void flight_free(flight_t *flight);
+
+#endif
diff --git a/trabalho-pratico/include/types/includes_breakfast.h b/trabalho-pratico/include/types/includes_breakfast.h
new file mode 100644
index 0000000..1064a40
--- /dev/null
+++ b/trabalho-pratico/include/types/includes_breakfast.h
@@ -0,0 +1,72 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  includes_breakfast.h
+ * @brief Includes breakfast of a ::reservation_t.
+ */
+
+#ifndef INCLUDES_BREAKFAST_H
+#define INCLUDES_BREAKFAST_H
+
+/**
+ * @brief   Indicates if breakfast is included for a ::reservation_t.
+ * @details For the values `INCLUDES_BREAKFAST_0`, `INCLUDES_BREAKFAST_NO_INPUT`,
+ *          `INCLUDES_BREAKFAST_F` and `INCLUDES_BREAKFAST_FALSE` a breakfast is not included, for
+ *          every other value the reservation includes breakfast.
+ */
+typedef enum includes_breakfast {
+    INCLUDES_BREAKFAST_0,
+    INCLUDES_BREAKFAST_1,
+    INCLUDES_BREAKFAST_NO_INPUT,
+    INCLUDES_BREAKFAST_F,
+    INCLUDES_BREAKFAST_FALSE,
+    INCLUDES_BREAKFAST_T,
+    INCLUDES_BREAKFAST_TRUE
+} includes_breakfast_t;
+
+/**
+ * @brief Parses a reservation's inclusion of breakfast.
+ *
+ * @param output Where the parsed value will be placed (only on success).
+ * @param input  Input (`"0"`,`"1"`, NULL (no input), `"f"`, `"false"`, `"t"` or `"true"`).
+ *
+ * @retval 0 Parsing success
+ * @retval 1 Parsing failure
+ */
+int includes_breakfast_from_string(includes_breakfast_t *output, const char *input);
+
+/**
+ * @brief The minimum number of characters (including null terminator) needed to write an "includes
+ *        breakfast" field to a buffer using ::includes_breakfast_sprintf.
+ * @details
+ *
+ * | F | A | L | S | E | \0 |
+ * | - | - | - | - | - | -- |
+ * | 1 | 2 | 3 | 4 | 5 | 6  |
+ */
+#define INCLUDES_BREAKFAST_SPRINTF_MIN_BUFFER_SIZE 4
+
+/**
+ * @brief Prints an "includes breakfast" field using `sprintf`.
+ *
+ * @param output    Where to print the airport code to. Must be at least
+ *                  ::INCLUDES_BREAKFAST_SPRINTF_MIN_BUFFER_SIZE long.
+ * @param breakfast "Includes breakfast" field.
+ */
+void includes_breakfast_sprintf(char *output, includes_breakfast_t breakfast);
+
+#endif
diff --git a/trabalho-pratico/include/types/reservation.h b/trabalho-pratico/include/types/reservation.h
new file mode 100644
index 0000000..b90c015
--- /dev/null
+++ b/trabalho-pratico/include/types/reservation.h
@@ -0,0 +1,216 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     reservation.h
+ * @brief    Declaration of type ::reservation_t.
+ *
+ * @details  In this module you can find a declaration of the type `reservation_t` as a struct
+ *           reservation, as well as getter and setter functions, which allow's the developer
+ *           access to any previously created reservation, or gives them the ability to create a
+ *           new reservation.
+ *
+ *           You can see what fields define a reservation (and thus available through getters and
+ *           setters) in the [struct's documentation](@ref reservation).
+ */
+#ifndef RESERVATION_H
+#define RESERVATION_H
+
+#include "types/includes_breakfast.h"
+#include "utils/date.h"
+
+/**
+ * @brief Type `reservation_t` defined as a struct reservation, that stores valuable information of
+ *        a given reservation.
+ * @details It's an opaque type.
+ */
+typedef struct reservation reservation_t;
+
+/**
+ * @brief Creates a new reservation with uninitialized fields.
+ * @return A `malloc`-allocated reservation (`NULL` on allocation failure).
+ */
+reservation_t *reservation_create(void);
+
+/**
+ * @brief Sets the reservation's user identifier.
+ * @details @p user_id will not get owned by @p reservation, and you should free it later.
+ *
+ * @param reservation Reservation to have its user identifier set.
+ * @param user_id     User identifier of the reservation.
+ */
+void reservation_set_user_id(reservation_t *reservation, char *user_id);
+
+/**
+ * @brief Sets the reservation's hotel name.
+ * @details @p hotel_name will not get owned by @p reservation, and you should free it later.
+ *
+ * @param reservation Reservation to have its hotel name set.
+ * @param hotel_name  Hotel name of the reservation.
+ */
+void reservation_set_hotel_name(reservation_t *reservation, char *hotel_name);
+
+/**
+ * @brief Sets the reservation's inclusion of breakfast.
+ * @param reservation        Reservation to have its inclusion of breakfast set.
+ * @param includes_breakfast A flag that gives information on the inclusion of breakfast of
+ *                           a reservation.
+ */
+void reservation_set_includes_breakfast(reservation_t       *reservation,
+                                        includes_breakfast_t includes_breakfast);
+
+/**
+ * @brief Sets the reservation's beginning date.
+ * @param reservation Reservation to have its beginning date set.
+ * @param begin_date  Beginning date of the reservation.
+ */
+void reservation_set_begin_date(reservation_t *reservation, date_t begin_date);
+
+/**
+ * @brief Sets the reservation's end date.
+ * @param reservation Reservation to have its end date set.
+ * @param end_date    End date of the reservation.
+ */
+void reservation_set_end_date(reservation_t *reservation, date_t end_date);
+
+/**
+ * @brief Sets the reservation's identifier.
+ * @param reservation Reservation to have its identifier set.
+ * @param id          Identifier of the reservation.
+ */
+void reservation_set_id(reservation_t *reservation, size_t id);
+
+/**
+ * @brief Sets the reservation's rating.
+ * @param reservation Reservation to have its rating set.
+ * @param rating      Rating of the reservation.
+ */
+void reservation_set_rating(reservation_t *reservation, int rating);
+
+/**
+ * @brief Sets the reservation's hotel identifier.
+ * @param reservation Reservation to have its hotel identifier set.
+ * @param hotel_id    Hotel identifier of the reservation.
+ */
+void reservation_set_hotel_id(reservation_t *reservation, int hotel_id);
+
+/**
+ * @brief Sets the reservation's hotel stars.
+ * @param reservation Reservation to have its hotel stars set.
+ * @param hotel_stars Hotel stars of the reservation.
+ */
+void reservation_set_hotel_stars(reservation_t *reservation, int hotel_stars);
+
+/**
+ * @brief Sets the reservation's city tax.
+ * @param reservation Reservation to have its city tax set.
+ * @param city_tax    City tax of the reservation.
+ */
+void reservation_set_city_tax(reservation_t *reservation, int city_tax);
+
+/**
+ * @brief Sets the reservation's price per night.
+ * @param reservation     Reservation to have its price per night set.
+ * @param price_per_night Price per night of the reservation.
+ */
+void reservation_set_price_per_night(reservation_t *reservation, int price_per_night);
+
+/**
+ * @brief  Gets the reservation's user identifier.
+ * @param  reservation Reservation to get the user identifier from.
+ * @return The reservation's user identifier, with modifications not allowed.
+ */
+const char *reservation_get_const_user_id(const reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's hotel name.
+ * @param  reservation Reservation to get the hotel name from.
+ * @return The reservation's hotel name, with modifications not allowed.
+ */
+const char *reservation_get_const_hotel_name(const reservation_t *reservation);
+
+/**
+ * @brief  Gets information on the inclusion of breakfast of the reservation.
+ * @param  reservation Reservation to get the `includes_breakfast` flag from.
+ * @return The reservation's flag `includes_breakfast`.
+ */
+includes_breakfast_t reservation_get_includes_breakfast(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's beginning date.
+ * @param  reservation Reservation to get the beginning date from.
+ * @return The reservation's beginning date.
+ */
+date_t reservation_get_begin_date(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's end date.
+ * @param  reservation Reservation to get the end date from.
+ * @return The reservation's end date.
+ */
+date_t reservation_get_end_date(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's identifier.
+ * @param  reservation Reservation to get the identifier from.
+ * @return The reservation's identifier.
+ */
+size_t reservation_get_id(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's rating.
+ * @param  reservation Reservation to get the rating from.
+ * @return The reservation's rating.
+ */
+int reservation_get_const_rating(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's hotel identifier.
+ * @param  reservation Reservation to get the hotel identifier from.
+ * @return The reservation's hotel identifier.
+ */
+int reservation_get_const_hotel_id(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's hotel stars.
+ * @param  reservation Reservation to get the hotel stars from.
+ * @return The reservation's hotel stars.
+ */
+int reservation_get_hotel_stars(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's city tax.
+ * @param  reservation Reservation to get the city tax from.
+ * @return The reservation's city tax.
+ */
+int reservation_get_city_tax(reservation_t *reservation);
+
+/**
+ * @brief  Gets the reservation's price per night.
+ * @param  reservation Reservation to get the price per night from.
+ * @return The reservation's price per night.
+ */
+int reservation_get_price_per_night(reservation_t *reservation);
+
+/**
+ * @brief             Frees the memory used for a given reservation.
+ * @details           All strings inside the reservation won't be freed, as they're not owned by the
+ *                    reservation.
+ * @param reservation Reservation to be deleted.
+ */
+void reservation_free(reservation_t *reservation);
+
+#endif
diff --git a/trabalho-pratico/include/types/sex.h b/trabalho-pratico/include/types/sex.h
new file mode 100644
index 0000000..a3d42a8
--- /dev/null
+++ b/trabalho-pratico/include/types/sex.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     sex.h
+ * @brief    Sex of a ::user_t.
+ */
+
+#ifndef SEX_H
+#define SEX_H
+
+/** @brief The sex of a ::user_t. */
+typedef enum {
+    SEX_F, /**< @brief Female */
+    SEX_M  /**< @brief Male */
+} sex_t;
+
+/**
+ * @brief Parses a user sex.
+ *
+ * @param output Where the parsed sex will be placed (only on success).
+ * @param input  Input (`"M"` or `"F"`).
+ *
+ * @retval 0 Parsing success
+ * @retval 1 Parsing failure
+ */
+int sex_from_string(sex_t *output, const char *input);
+
+#endif
diff --git a/trabalho-pratico/include/types/user.h b/trabalho-pratico/include/types/user.h
new file mode 100644
index 0000000..c821429
--- /dev/null
+++ b/trabalho-pratico/include/types/user.h
@@ -0,0 +1,180 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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     user.h
+ * @brief    Declaration of type ::user_t.
+ *
+ * @details  In this module you can find a declaration of the type `user_t`, as well as getter and
+ *           setter functions, which allow the developer to access any previously created user, and
+ *           functions to create new users.
+ *
+ *           You can see what fields define a user (and thus available through getters and setters)
+ *           in the [struct's documentation](@ref user).
+ */
+
+#ifndef USER_H
+#define USER_H
+
+#include "types/account_status.h"
+#include "types/country_code.h"
+#include "types/sex.h"
+#include "utils/date.h"
+#include "utils/date_and_time.h"
+
+/**
+ * @brief   Type `user_t` defined as a struct user, that stores valuable information of a given
+ *          person.
+ * @details It's an opaque type.
+ */
+typedef struct user user_t;
+
+/**
+ * @brief Creates a new user with uninitialized fields.
+ * @return A `malloc`-allocated user (`NULL` on allocation failure).
+ */
+user_t *user_create(void);
+
+/**
+ * @brief Sets the user's identifier.
+ * @details @p id will not get owned by @p user, and you should free it later.
+ *
+ * @param user User to have its identifier set.
+ * @param id   Id of the user.
+ */
+void user_set_id(user_t *user, char *id);
+
+/**
+ * @brief Sets the user's name.
+ * @details @p name will not get owned by @p user, and you should free it later.
+ *
+ * @param user User to have its name set.
+ * @param name Name of the user.
+ */
+void user_set_name(user_t *user, char *name);
+
+/**
+ * @brief Sets the user's birth date.
+ *
+ * @param user User to have its birth date set.
+ * @param date Birth date of the user.
+ */
+void user_set_birth_date(user_t *user, date_t date);
+
+/**
+ * @brief Sets the user's passport.
+ * @details @p passport will not get owned by @p user, and you should free it later.
+ *
+ * @param user     User to have its passport set.
+ * @param passport Passport number of the user.
+ */
+void user_set_passport(user_t *user, char *passport);
+
+/**
+ * @brief Sets the user's country code.
+ *
+ * @param user         User to have its country code set.
+ * @param country_code Country code of the user.
+ */
+void user_set_country_code(user_t *user, country_code_t country_code);
+
+/**
+ * @brief Sets the user's sex.
+ *
+ * @param user User to have its sex set.
+ * @param sex  Sex of the user.
+ */
+void user_set_sex(user_t *user, sex_t sex);
+
+/**
+ * @brief Sets the user's account status.
+ *
+ * @param user           User to have its account status set.
+ * @param account_status Whether the user's account is active or inactive.
+ */
+void user_set_account_status(user_t *user, account_status_t account_status);
+
+/**
+ * @brief Sets the user's account creation date.
+ *
+ * @param user User to have its account status set.
+ * @param date Account creation date of the user.
+ */
+void user_set_account_creation_date(user_t *user, date_and_time_t date);
+
+/**
+ * @brief Gets the user's identifier.
+ * @param user User to get id from.
+ * @return The user's identifier, with modifications not allowed.
+ */
+const char *user_get_const_id(const user_t *user);
+
+/**
+ * @brief Gets the user name.
+ * @param user User to get name from.
+ * @return The user's name, with modifications not allowed.
+ */
+const char *user_get_const_name(const user_t *user);
+
+/**
+ * @brief Gets the user's birth date.
+ * @param user User to get birth date from.
+ * @return The user's birth date.
+ */
+date_t user_get_birth_date(const user_t *user);
+
+/**
+ * @brief Gets the user passport.
+ * @param user User to get passport number from.
+ * @return The user's passport number, with modifications not allowed.
+ */
+const char *user_get_const_passport(const user_t *user);
+
+/**
+ * @brief Gets the user's country code.
+ * @param user User to get country code from.
+ */
+country_code_t user_get_country_code(const user_t *user);
+
+/**
+ * @brief Gets the user's sex.
+ * @param user User to get sex from.
+ * @return The user's sex.
+ */
+sex_t user_get_sex(const user_t *user);
+
+/**
+ * @brief Gets the user's account_status.
+ * @param user User to get account status from.
+ * @return The user's account status.
+ */
+account_status_t user_get_account_status(const user_t *user);
+
+/**
+ * @brief Gets the user's account creation date.
+ * @param user User to get account create date from.
+ * @return The user's account creation date.
+ */
+date_and_time_t user_get_account_creation_date(const user_t *user);
+
+/**
+ * @brief      Frees the memory used for a given user.
+ * @details    All strings inside the user won't be freed, as they're not owned by the user.
+ * @param user User to be deleted.
+ */
+void user_free(user_t *user);
+
+#endif
diff --git a/trabalho-pratico/src/test.c b/trabalho-pratico/src/test.c
index 17e98a0..bbbb4e1 100644
--- a/trabalho-pratico/src/test.c
+++ b/trabalho-pratico/src/test.c
@@ -22,43 +22,36 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-#include "utils/string_pool.h"
-
-/** @brief Number of characters in a pool block. In practice, this should be way larger. */
-#define TEST_POOL_BLOCK_SIZE 32
-
-/** @brief Number of pool items to be allocated */
-#define TEST_NUM_ITEMS 10000
+#include "types/airport_code.h"
 
 /**
  * @brief The entry point to the test program.
- * @details Tests for string pools.
+ * @details Test for airport codes.
  * @retval 0 Success
  * @retval 1 Insuccess
  */
 int main(void) {
-    string_pool_t *pool = string_pool_create(TEST_POOL_BLOCK_SIZE);
-
-    const char *long_string =
-        "This string is longer than a single block, but the pool can still handle it!";
-    const char *short_string = "Hello, world!";
-
-    char *allocated[TEST_NUM_ITEMS] = {0};
-    for (size_t i = 0; i < TEST_NUM_ITEMS; ++i) {
-        int r = rand() % 2 == 1;
-
-        allocated[i] = string_pool_put(pool, r ? short_string : long_string);
-        if (!allocated[i]) {
-            fputs("Allocation error!\n", stderr);
-            string_pool_free(pool);
-            return 1;
+    const char *string_codes[6] = {
+        "",     /* Too short */
+        "O",    /* Too short */
+        "OP",   /* Too short */
+        "OPO",  /* Just right */
+        "oPo",  /* Everything should be converted to upper-case */
+        "OPOR", /* Too long */
+    };
+
+    for (int i = 0; i < 6; ++i) {
+        airport_code_t parsed;
+
+        if (!airport_code_from_string(&parsed, string_codes[i])) {
+            char back_to_string[AIRPORT_CODE_SPRINTF_MIN_BUFFER_SIZE];
+            airport_code_sprintf(back_to_string, parsed);
+            printf("Parsed code: \"%s\"\n", back_to_string);
+
+        } else {
+            fprintf(stderr, "Failed to parse airport code \"%s\"!\n", string_codes[i]);
         }
     }
 
-    for (size_t i = 0; i < TEST_NUM_ITEMS; ++i) {
-        printf("%s\n", allocated[i]);
-    }
-
-    string_pool_free(pool);
     return 0;
 }
diff --git a/trabalho-pratico/src/types/account_status.c b/trabalho-pratico/src/types/account_status.c
new file mode 100644
index 0000000..356a5f6
--- /dev/null
+++ b/trabalho-pratico/src/types/account_status.c
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  account_status.c
+ * @brief Implementation of methods in include/types/account_status.h
+ */
+
+#include <ctype.h>
+#include <string.h>
+
+#include "types/account_status.h"
+
+/** @brief Value of `strlen("inactive")`. */
+#define ACCOUNT_STATUS_STRLEN_INACTIVE 8
+
+int account_status_from_string(account_status_t *output, const char *input) {
+    size_t len = strlen(input);
+    if (len > ACCOUNT_STATUS_STRLEN_INACTIVE)
+        return 1; /* Too long for "inactive" */
+
+    char lower_case[ACCOUNT_STATUS_STRLEN_INACTIVE + 1];
+    for (size_t i = 0; i < len; ++i)
+        lower_case[i] = tolower(input[i]);
+    lower_case[len] = '\0';
+
+    if (strcmp(lower_case, "inactive") == 0) {
+        *output = ACCOUNT_STATUS_INACTIVE;
+        return 0;
+    } else if (strcmp(lower_case, "active") == 0) {
+        *output = ACCOUNT_STATUS_ACTIVE;
+        return 0;
+    } else {
+        return 1;
+    }
+}
diff --git a/trabalho-pratico/src/types/airport_code.c b/trabalho-pratico/src/types/airport_code.c
new file mode 100644
index 0000000..eed6e05
--- /dev/null
+++ b/trabalho-pratico/src/types/airport_code.c
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  airport_code.c
+ * @brief Implementation of methods in include/types/airport_code.h
+ *
+ * ### Examples
+ * See [the header file's documentation](@ref airport_code_examples).
+ */
+
+#include <ctype.h>
+
+#include "types/airport_code.h"
+
+int airport_code_from_string(airport_code_t *output, const char *input) {
+    if (*input && *(input + 1) && *(input + 2) && !*(input + 3) && isalpha(*input) &&
+        isalpha(*(input + 1)) && isalpha(*(input + 2))) {
+
+        *((char *) output)       = toupper(input[0]);
+        *(((char *) output) + 1) = toupper(input[1]);
+        *(((char *) output) + 2) = toupper(input[2]);
+        *(((char *) output) + 3) = '\0';
+        return 0;
+    }
+    return 1;
+}
+
+void airport_code_sprintf(char *output, airport_code_t airport) {
+    *((airport_code_t *) output) = airport;
+}
diff --git a/trabalho-pratico/src/types/country_code.c b/trabalho-pratico/src/types/country_code.c
new file mode 100644
index 0000000..b93d186
--- /dev/null
+++ b/trabalho-pratico/src/types/country_code.c
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  country_code.c
+ * @brief Implementation of methods in include/types/country_code.h
+ *
+ * ### Examples
+ * See [the header file's documentation](@ref country_code_examples).
+ */
+
+#include <ctype.h>
+
+#include "types/country_code.h"
+
+int country_code_from_string(country_code_t *output, const char *input) {
+    if (*input && *(input + 1) && !*(input + 2) && isalpha(*input) && isalpha(*(input + 1))) {
+        *output = *(country_code_t *) input;
+        return 0;
+    }
+    return 1;
+}
+
+void country_code_sprintf(char *output, country_code_t country) {
+    *((country_code_t *) output) = country;
+    output[2]                    = '\0';
+}
diff --git a/trabalho-pratico/src/types/flight.c b/trabalho-pratico/src/types/flight.c
new file mode 100644
index 0000000..b272988
--- /dev/null
+++ b/trabalho-pratico/src/types/flight.c
@@ -0,0 +1,157 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  flight.c
+ * @brief Implementation of methods in include/types/flight.h
+ */
+#include <stdlib.h>
+
+#include "types/flight.h"
+
+/**
+ * @struct flight
+ * @brief Represents a flight in the datasets.
+ * @details NOTE: some fields in the project's requirements (such as real arrival date, pilot,
+ *          copilot and notes) aren't put here, as they won't be required by any
+ *          database query.
+ *
+ * @var flight::airline
+ *     @brief Airline of a given flight.
+ * @var flight::plane_model
+ *     @brief Plane model of a given flight.
+ * @var flight::origin
+ *     @brief Airport of origin of the flight.
+ * @var flight::destination
+ *     @brief Airport of origin of the flight.
+ * @var flight::id
+ *     @brief Identifier of a given flight.
+ * @var flight::schedule_departure_date
+ *     @brief Scheduled departure date of a given flight.
+ * @var flight::real_departure_date
+ *     @brief Real departure date of a given flight.
+ * @var flight::schedule_arrival_date
+ *     @brief Scheduled arrival date of a given flight.
+ * @var flight::number_of_passengers
+ *     @brief Number of passengers of a given flight.
+ * @var flight::total_seats
+ *     @brief Number of total seats of a given flight.
+ */
+struct flight {
+    char           *airline;
+    char           *plane_model;
+    airport_code_t  origin;
+    airport_code_t  destination;
+    size_t          id;
+    date_and_time_t schedule_departure_date;
+    date_and_time_t real_departure_date;
+    date_and_time_t schedule_arrival_date;
+    int             number_of_passengers;
+    int             total_seats;
+};
+
+flight_t *flight_create(void) {
+    return malloc(sizeof(struct flight));
+}
+
+void flight_set_airline(flight_t *flight, char *airline) {
+    flight->airline = airline;
+}
+
+void flight_set_plane_model(flight_t *flight, char *plane_model) {
+    flight->plane_model = plane_model;
+}
+
+void flight_set_origin(flight_t *flight, airport_code_t origin) {
+    flight->origin = origin;
+}
+
+void flight_set_destination(flight_t *flight, airport_code_t destination) {
+    flight->destination = destination;
+}
+
+void flight_set_id(flight_t *flight, size_t id) {
+    flight->id = id;
+}
+
+void flight_set_schedule_departure_date(flight_t       *flight,
+                                        date_and_time_t scheduled_departure_date) {
+    flight->schedule_departure_date = scheduled_departure_date;
+}
+
+void flight_set_schedule_arrival_date(flight_t *flight, date_and_time_t schedule_arrival_date) {
+    flight->schedule_arrival_date = schedule_arrival_date;
+}
+
+void flight_increment_number_of_passengers(flight_t *flight, int increment_factor) {
+    flight->number_of_passengers += increment_factor;
+}
+
+void flight_set_number_of_passengers(flight_t *flight, int number_of_passengers) {
+    flight->number_of_passengers = number_of_passengers;
+}
+
+void flight_set_real_departure_date(flight_t *flight, date_and_time_t real_departure_date) {
+    flight->real_departure_date = real_departure_date;
+}
+
+void flight_set_total_seats(flight_t *flight, int total_seats) {
+    flight->total_seats = total_seats;
+}
+
+const char *flight_get_const_airline(const flight_t *flight) {
+    return flight->airline;
+}
+
+const char *flight_get_const_plane_model(const flight_t *flight) {
+    return flight->plane_model;
+}
+
+airport_code_t flight_get_origin(const flight_t *flight) {
+    return flight->origin;
+}
+
+airport_code_t flight_get_destination(const flight_t *flight) {
+    return flight->destination;
+}
+
+size_t flight_get_id(const flight_t *flight) {
+    return flight->id;
+}
+
+date_and_time_t flight_get_schedule_departure_date(const flight_t *flight) {
+    return flight->schedule_departure_date;
+}
+
+date_and_time_t flight_get_schedule_arrival_date(const flight_t *flight) {
+    return flight->schedule_arrival_date;
+}
+
+int flight_get_number_of_passengers(const flight_t *flight) {
+    return flight->number_of_passengers;
+}
+
+date_and_time_t flight_get_real_departure_date(const flight_t *flight) {
+    return flight->real_departure_date;
+}
+
+int flight_get_total_seats(const flight_t *flight) {
+    return flight->total_seats;
+}
+
+void flight_free(flight_t *flight) {
+    free(flight);
+}
diff --git a/trabalho-pratico/src/types/includes_breakfast.c b/trabalho-pratico/src/types/includes_breakfast.c
new file mode 100644
index 0000000..2582b80
--- /dev/null
+++ b/trabalho-pratico/src/types/includes_breakfast.c
@@ -0,0 +1,79 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  includes_breakfast.c
+ * @brief Implementation of methods in include/types/includes_breakfast.h
+ */
+#include <string.h>
+
+#include "types/includes_breakfast.h"
+
+int includes_breakfast_from_string(includes_breakfast_t *output, const char *input) {
+    if (*input == '\0') {
+        *output = INCLUDES_BREAKFAST_NO_INPUT;
+        return 0;
+    } else if (strcmp(input, "f") == 0) {
+        *output = INCLUDES_BREAKFAST_F;
+        return 0;
+    } else if (strcmp(input, "false") == 0) {
+        *output = INCLUDES_BREAKFAST_FALSE;
+        return 0;
+    } else if (strcmp(input, "t") == 0) {
+        *output = INCLUDES_BREAKFAST_T;
+        return 0;
+    } else if (strcmp(input, "true") == 0) {
+        *output = INCLUDES_BREAKFAST_TRUE;
+        return 0;
+    } else if (strcmp(input, "1") == 0) {
+        *output = INCLUDES_BREAKFAST_1;
+        return 0;
+    } else if (strcmp(input, "0") == 0) {
+        *output = INCLUDES_BREAKFAST_0;
+        return 0;
+    }
+    return 1;
+}
+
+void includes_breakfast_sprintf(char *output, includes_breakfast_t breakfast) {
+    const char *source = "";
+
+    switch (breakfast) {
+        case INCLUDES_BREAKFAST_0:
+            source = "0";
+            break;
+        case INCLUDES_BREAKFAST_1:
+            source = "1";
+            break;
+        case INCLUDES_BREAKFAST_NO_INPUT:
+            source = "";
+            break;
+        case INCLUDES_BREAKFAST_F:
+            source = "f";
+            break;
+        case INCLUDES_BREAKFAST_FALSE:
+            source = "false";
+            break;
+        case INCLUDES_BREAKFAST_T:
+            source = "t";
+            break;
+        case INCLUDES_BREAKFAST_TRUE:
+            source = "true";
+            break;
+    }
+
+    strcpy(output, source);
+}
diff --git a/trabalho-pratico/src/types/reservation.c b/trabalho-pratico/src/types/reservation.c
new file mode 100644
index 0000000..f273e5c
--- /dev/null
+++ b/trabalho-pratico/src/types/reservation.c
@@ -0,0 +1,164 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  reservation.c
+ * @brief Implementation of methods in include/types/reservation.h
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "types/reservation.h"
+
+/**
+ * @struct reservation
+ * @brief Represents a reservation in the datasets.
+ * @details NOTE: some fields in the project's requirements (such as address, room details and
+ *          comments) aren't put here, as they won't be required by any database query.
+ *
+ * @var reservation::user_id
+ *     @brief User identifier of a given reservation.
+ * @var reservation::hotel_name
+ *     @brief Hotel name of a given reservation.
+ * @var reservation::includes_breakfast
+ *     @brief Flag identifying the inclusion of breakfast of a given reservation.
+ * @var reservation::begin_date
+ *     @brief The beginning date of a given reservation.
+ * @var reservation::end_date
+ *     @brief End date of a given reservation.
+ * @var reservation::id
+ *     @brief Identifier of a given reservation.
+ * @var reservation::rating
+ *     @brief Rating (equals `-1` if it wasn't given) of a given reservation.
+ * @var reservation::hotel_id
+ *     @brief Hotel identifier of a given reservation.
+ * @var reservation::hotel_stars
+ *     @brief Hotel stars of a given reservation.
+ * @var reservation::city_tax
+ *     @brief City tax of a given reservation.
+ * @var reservation::price_per_night
+ *     @brief Price per night of a given reservation.
+ */
+struct reservation {
+    char                   *user_id;
+    char                   *hotel_name;
+    enum includes_breakfast includes_breakfast;
+    date_t                  begin_date;
+    date_t                  end_date;
+    size_t                  id;
+    int                     rating;
+    int                     hotel_id;
+    int                     hotel_stars;
+    int                     city_tax;
+    int                     price_per_night;
+};
+
+reservation_t *reservation_create(void) {
+    return malloc(sizeof(struct reservation));
+}
+
+void reservation_set_user_id(reservation_t *reservation, char *user_id) {
+    reservation->user_id = user_id;
+}
+
+void reservation_set_hotel_name(reservation_t *reservation, char *hotel_name) {
+    reservation->hotel_name = hotel_name;
+}
+
+void reservation_set_includes_breakfast(reservation_t       *reservation,
+                                        includes_breakfast_t includes_breakfast) {
+    reservation->includes_breakfast = includes_breakfast;
+}
+
+void reservation_set_begin_date(reservation_t *reservation, date_t begin_date) {
+    reservation->begin_date = begin_date;
+}
+
+void reservation_set_end_date(reservation_t *reservation, date_t end_date) {
+    reservation->end_date = end_date;
+}
+
+void reservation_set_id(reservation_t *reservation, size_t id) {
+    reservation->id = id;
+}
+
+void reservation_set_rating(reservation_t *reservation, int rating) {
+    reservation->rating = rating;
+}
+
+void reservation_set_hotel_id(reservation_t *reservation, int hotel_id) {
+    reservation->hotel_id = hotel_id;
+}
+
+void reservation_set_hotel_stars(reservation_t *reservation, int hotel_stars) {
+    reservation->hotel_stars = hotel_stars;
+}
+
+void reservation_set_city_tax(reservation_t *reservation, int city_tax) {
+    reservation->city_tax = city_tax;
+}
+
+void reservation_set_price_per_night(reservation_t *reservation, int price_per_night) {
+    reservation->price_per_night = price_per_night;
+}
+
+const char *reservation_get_const_user_id(const reservation_t *reservation) {
+    return reservation->user_id;
+}
+
+const char *reservation_get_const_hotel_name(const reservation_t *reservation) {
+    return reservation->hotel_name;
+}
+
+includes_breakfast_t reservation_get_includes_breakfast(reservation_t *reservation) {
+    return reservation->includes_breakfast;
+}
+
+date_t reservation_get_begin_date(reservation_t *reservation) {
+    return reservation->begin_date;
+}
+
+date_t reservation_get_end_date(reservation_t *reservation) {
+    return reservation->end_date;
+}
+
+size_t reservation_get_id(reservation_t *reservation) {
+    return reservation->id;
+}
+
+int reservation_get_const_rating(reservation_t *reservation) {
+    return reservation->rating;
+}
+
+int reservation_get_const_hotel_id(reservation_t *reservation) {
+    return reservation->hotel_id;
+}
+
+int reservation_get_hotel_stars(reservation_t *reservation) {
+    return reservation->hotel_stars;
+}
+
+int reservation_get_city_tax(reservation_t *reservation) {
+    return reservation->city_tax;
+}
+
+int reservation_get_price_per_night(reservation_t *reservation) {
+    return reservation->price_per_night;
+}
+
+void reservation_free(reservation_t *reservation) {
+    free(reservation);
+}
diff --git a/trabalho-pratico/src/types/sex.c b/trabalho-pratico/src/types/sex.c
new file mode 100644
index 0000000..9f4ce40
--- /dev/null
+++ b/trabalho-pratico/src/types/sex.c
@@ -0,0 +1,36 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  sex.c
+ * @brief Implementation of methods in include/types/sex.h
+ */
+
+#include <string.h>
+
+#include "types/sex.h"
+
+int sex_from_string(sex_t *output, const char *input) {
+    if (strcmp(input, "M") == 0) {
+        *output = SEX_M;
+        return 0;
+    } else if (strcmp(input, "F") == 0) {
+        *output = SEX_F;
+        return 0;
+    } else {
+        return 1;
+    }
+}
diff --git a/trabalho-pratico/src/types/user.c b/trabalho-pratico/src/types/user.c
new file mode 100644
index 0000000..3aa7a07
--- /dev/null
+++ b/trabalho-pratico/src/types/user.c
@@ -0,0 +1,131 @@
+/*
+ * Copyright 2023 Humberto Gomes, José Lopes, José Matos
+ *
+ * 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  user.c
+ * @brief Implementation of methods in include/types/user.h
+ */
+
+#include <stdlib.h>
+
+#include "types/user.h"
+
+/**
+ * @struct user
+ * @brief Represents a user in the datasets.
+ * @details NOTE: some fields in the project's requirements (such as emails, phone numbers,
+ *          addresses and payment methods) aren't put here, as they won't be required by any
+ *          database query.
+ *
+ * @var user::id
+ *     @brief Identifier of a given user.
+ * @var user::name
+ *     @brief Full name of a given user.
+ * @var user::birth_date
+ *     @brief Date of birth of the user.
+ * @var user::sex
+ *     @brief Sex of the user.
+ * @var user::passport
+ *     @brief Passport number of a given user.
+ * @var user::country_code
+ *     @brief Code of the country of a given user.
+ * @var user::account_creation_date
+ *     @brief Date of creation of the user's account.
+ * @var user::account_status
+ *     @brief Whether a user's account is active or inactive.
+ */
+struct user {
+    char            *id;
+    char            *name;
+    date_t           birth_date;
+    char            *passport;
+    country_code_t   country_code;
+    sex_t            sex;
+    account_status_t account_status;
+    date_and_time_t  account_creation_date;
+};
+
+user_t *user_create(void) {
+    return malloc(sizeof(struct user));
+}
+
+void user_set_id(user_t *user, char *id) {
+    user->id = id;
+}
+
+void user_set_name(user_t *user, char *name) {
+    user->name = name;
+}
+
+void user_set_birth_date(user_t *user, date_t date) {
+    user->birth_date = date;
+}
+
+void user_set_passport(user_t *user, char *passport) {
+    user->passport = passport;
+}
+
+void user_set_country_code(user_t *user, country_code_t country_code) {
+    user->country_code = country_code;
+}
+
+void user_set_sex(user_t *user, sex_t sex) {
+    user->sex = sex;
+}
+
+void user_set_account_status(user_t *user, account_status_t account_status) {
+    user->account_status = account_status;
+}
+
+void user_set_account_creation_date(user_t *user, date_and_time_t date) {
+    user->account_creation_date = date;
+}
+
+const char *user_get_const_id(const user_t *user) {
+    return user->id;
+}
+
+const char *user_get_const_name(const user_t *user) {
+    return user->name;
+}
+
+date_t user_get_birth_date(const user_t *user) {
+    return user->birth_date;
+}
+
+const char *user_get_const_passport(const user_t *user) {
+    return user->passport;
+}
+
+country_code_t user_get_country_code(const user_t *user) {
+    return user->country_code;
+}
+
+sex_t user_get_sex(const user_t *user) {
+    return user->sex;
+}
+
+account_status_t user_get_account_status(const user_t *user) {
+    return user->account_status;
+}
+
+date_and_time_t user_get_account_creation_date(const user_t *user) {
+    return user->account_creation_date;
+}
+
+void user_free(user_t *user) {
+    free(user);
+}