mysql - ER 模型弱实体。

Question

根据这些说明，我正在尝试创建一个 ER 模型。和 这些说明:

Total Escapes has a wide variety of tours on offer to its customers. Each tour can be uniquely identified by a route ID. A tour also has associated with it an estimated duration and a description of the tour itself.

Customer details are to be recorded in the database, with a unique customer ID generated for each customer. Additional details include a name, date of birth and contact phone number. A Tour run is defined as one instance of a tour, i.e. a tour has a number of tour runs. For example, a ‘Melbourne City Tour’ runs twice every day, 8:30am and 2:30pm. In other words, a Tour run is identified by not only a specific tour but the date and time that tour was operated.

A customer can book tour runs. The price paid for the booking is recorded. A vehicle is used by a driver to perform his/her duties in taking tourists on a route. Each vehicle can be identified by it registration plates. Other attributes such as vehicle type, capacity and colour are also recorded.

A Tour guide organizes a tour run in coordination with the driver. The tour guide must have a unique certificate number to be recorded in the system. Their name, mobile number and address are also required. The driver responsible for operating the tour vehicle on a tour run can be identified by their D/L number. A name and mobile phone number are also recorded in the database for each driver.

Some tour guides train other tour guides to manage tours themselves. Each trainee has one supervisor while a supervisor can guide many trainees.

在我创建的图表上，我想知道实例和游览之间的链接是否是多对一？

或者巡回赛甚至不是一个弱实体？

ER Model

Answer 1

我同意 Tour Run 是一个弱实体 - 说明对此非常具体。这意味着Instance 是一种标识关系，将Route_ID 值映射到Route_ID,Date,Time 值。这是一个微不足道的关系，不需要与 Tour Run 键分开记录。您也正确地认为 Instance 和 Tour 之间的关联是多对一的 - 许多 Route_ID,Date,Time 三元组映射到一个Route_ID。