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An online house renting software is used for publishing houses and apartments $($houses for brief$)$ renting information and placing house renting orders. Landlords and tenants need to register in the software by creating an account with a unique username and password. Landlords $($or tenants$)$ can only publish house renting information $($place view appointments and contacts$)$ after their identities are authenticated by providing identity number and face recognition. For tenants, the software provides a Search$-$Result$-$List $($SRL$)$ to show a list of houses fulfilling given searching criteria, and a Recommended List $($RL$)$ to show houses recommended by the system. For landlords, the software has a My$-$House List $($MHL$)$ to show houses published by themselves. When publishing house renting information, landlords need to provide the price per month, location, room information, facilities, description, etc. The house renting information provided by landlords can be searched out by tenants only after the information is checked by system managers. For each house, there are several candidate viewing times for making appointments. Tenants could place appointments to view the conditions of houses in person. After the appointments are placed, landlords could agree or reject. After viewing the houses, tenants and landlords could place contacts to rent the houses.

$(1)$ Prepare a domain class diagram for this software including classes "User, Account, House, SRL$,$ RL$,$ MHL$,$ Appointment, Contact, etc" $(10\text{'})$

$(2)$ Add appropriate properties to classes in the domain class diagram $(5\text{'})$

$(3)$ Build a state diagram for the class "Appointment" including states "placed, agreed, rejected, terminated and canceled". Tips: after the appointment is agreed by the landlord, the appointment changes from the placed state to the agreed state. Otherwise, the appointment changes from the placed state to the canceled state. In the agreed state, the tenant views the house on time and the appointment changes to the terminated state. Tenants could also cancel the appointments. $(12\text{'})$