How to model a consitent database in alloy?

Question

Alloy newbie here. I'm trying to model a medical database containing user and some medical information.

sig User{
    name: one  String,
    surname:  one String,
    socialNumber:  one String,
    address:  one String,
    age: one Int,   
    registration: one UserCredential,
    healthStatus: one HealthInformation
}{
    age>0
}
sig UserCredential{
    user: one String,
    pass: one String,
    mail:  one String
}

sig HealthInformation{}


sig Data4Help{
    users: some User,
}

pred show(d:Data4Help){
    #d.users>1
}

run show for 10

The analyzer tell me the model is inconsistent:

Executing "Run show for 10" Solver=sat4j Bitwidth=4 MaxSeq=7 SkolemDepth=1 Symmetry=20 5448 vars. 510 primary vars. 12578 clauses. 16ms. No instance found. Predicate may be inconsistent. 0ms.

Can you guys tell me why? All I want is having the database "Data4Help" linked to some users, probably the definition of the relation is incorrect but I don't know why. Thank you

Answer 1

The problem is that Alloy has some troubles with Strings. By default, the String signature defines an empty set of atoms. If you want to use Strings in your model, you will have to populate that set with "your own Strings".

See How to use String in Alloy?

In your model, you could add this simple fact

fact initPoolOfString{ 
   String in "insert"+ "your"+"dummy" + "strings" + "here"
}