Assignment 4: Backend Design & Implementation ​

concept User

purpose authenticate a partipicant of RealTalk

state

registered: set User
username, password: registered -> one String

actions

register(n, p: String, out u: User)

u not in registered
registered += u
u.username := n
u.passowrd := p

authenticate(n, p: String, out u: User)

u in registered
u.username = n and u.password = p

operational principle

after a user registers with a username and password, they can authenticate with that same username and password
after register(n, p, u), u in registered, u.username = n, u.password = p; authenticate(n, p, u') results in u = u'

concept Session [User]

purpose authenticate users for an extended period of time

state

active: set Session
curUser: active -> one User

actions

start(u: User, out s: Session)

s not in active
active += s
s.curUser = u

end(s: Session)

s in active
active -= s

getUser(s: Session, out u: User)

s in active
u := s.curUser

operational principle

after a session starts until it ends, getUser returns the same user that started the session
after start(u, s) until end(s, u), getUser(s, u') results in u = u'

concept Friend [User]

purpose increase connections between others

state

friends: User -> set User

actions

friend(u1, u2: User)

u1.friends += u2
u2.friends += u1

unfriend(u1, u2: User)

when u2 in u1.friends
u1.friends -= u2
when u1 in u2.friends
u2.friends -= u1

areFriends(u1, u2: User, out b: Boolean)

when u2 in u1.friends or u1 in u2.friends
b := True
otherwise
b := False

operational principle

after a user friends another user, they are both considered each others friends until one of them unfriends the other
after friend(u1, u2) until unfriend(u1, u2), u2 in u1.friends, u1 in u2.friends, and areFriend(u1, u2, b) results in b = True

concept Post [User, Content]

purpose share content with others

state

posts: User -> set Post
content: Post -> one Content
author: Post -> one User

actions

post(u: User, c: Content, out p: Post)

p.content := c
p.author := u
u.posts += p

unpost(u: User, p: Post)

when p in u.posts u.posts -= p
forget content of p
forget author of p

operational principle

after post(u, p, c) until unpost(u, p), p in u.posts, u = p.author, and c = p.content

concept Comment [Target, User, Content]

purpose react to other content

state

comments: Target -> set Content
author: Content -> one User

actions

comment(t: Target, u: User, c: Content)

t.comments += c
store u as author c is from

uncomment(t: Target, u: User, c: Content)

when the author of c is u
t.comments -= c
forget author of c

operational principle

after comment(t, u, c) until uncomment(u, c), c in t.comments and u is author of c

concept Like [Target, User]

purpose show approval or disapproval of information

state

likes, dislikes: Target -> set User

actions

like(t: Target, u: User)

t.likes += u

dislike(t: Target, u: User)

t.dislikes += u

neutralize(t: Target, u: User)

when u in t.likes
t.likes -= u
when u in t.dislikes
t.dislikes -= u

operational principle

after like(t, u) until dislike(t, u) or neutralize(t, u), u in t.likes
after dislike(t, u) until like(t, u) or neutralize(t, u), u in t.dislikes

concept Trust [Target, User]

purpose show agreement or disagreement with the truthfulness of information

state

trusts, mistrusts: Target -> set User

actions

trust(t: Target, u: User)

t.trusts += u

mistrust(t: Target, u: User)

t.mistrusts += u

neutralize(t: Target, u: User)

when u in t.trusts
t.trusts -= u
when u in t.mistrusts
t.mistrusts -= u

operational principle

after trust(t, u) until mistrust(t, u) or neutralize(t, u), u in t.trusts
after mistrust(t, u) until trust(t, u) or neutralize(t, u), u in t.mistrusts

concept Karma [User]

purpose show how truthful a user is

state

karma: User -> one Integer

actions

increase(u: User)

when u in karma
u.karma := u.karma + 1
when u not in karma
u.karma := 1

decrease(u: User)

when u in karma
u.karma := u.karma - 1
when u not in karma
u.karma := -1

operational principle

after increase(u) until decrease(u), u.karma is 1 more than before
after decrease(u) until increase(u), u.karma is 1 less than before