Suggestion for a contact management database design

I am currently designing a contact management database for a chamber of commerce. The goal of the database is to store all the person (except our own staff), all recorded companies (regular companies and member of the chamber), addresses of the person and companies, tasks that the staff are currently responsible for, a list of our staff (user) and the roles within the chamber.

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Business Rules

• one person works for one company
• one company have multiple person
• person and company can have multiple address
• one company can be in multiple industry
• one industry can have multiple company
• one company can have multiple membertype
• one membertype can have multiple company
• one user can play multiple role
• one role can be assigned to mutliple user
• one user can have multiple task
• one task can be worked on by multiple user
• one task can target multiple person
• one person can be targeted by multiple task
• one person can only be added by one user
• one user can add multiple person
• one company can have 0 or 1 parent_company
• one parent_company can have multiple child company

I have come up with the following design and it has undergone some changes:

Issue

• Are there better ways to display the user-task-person relationship?
• For example, if a person can have only one email but can have multiple tel, should I make an extra table just for tel while email is still in the persontable? Would it considered to be “unclean”?
• For the table membertype, should company_id and typename both be PK?
• How does this schema look now? Are there still some normalisations to be done?

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I’m a newbee at database, there are definitely some design flaws or errors, it would be nice if you guys could give me some suggestions so that I can correct and improve this design. Thank you ^~^

Answer

The main issue I see is that while all primary keys are defined as Int some foreign keys or references are defined as varchar.

1. company in contact table
2. user_role in user table
3. parent_company in company
4. added_by in user table

Also role_id is length 10 while all other primary keys are 11.
Personally I would prefer capitalised table names, User, Company etc

Update for the edited version:

You might want to create a table for phone, mail,fax etc say contact_info that could contain a string field holding the contact info and a type field (email, phone, fax,…). This way you could store several phone numbers for instance, if you want to limit email to one you could either leave it in the person table and not allow it here or have a business rule to only allow one email row in contact_info.

This table could also be useful for company if you want to store email or phone numbers for the company like [e-mail] or the number to the company switchboard

For the table membertype, should company_id and typename both be PK?

Yes

Second update About the address solution: Shouldn’t the address table contain enough info to make each address unique, I can understand that a company can have more than one address but should it allowed for two companies to have the same address (by that I mean the same row in the database) so maybe it should be changed to a one-to-many from company and ´address´ but a one-to-one in the other direction.
I also think it could be good to have some kind of label in the two address-link tables so one can easily identify an address like “home”, “work”, “Office”, “Warehouse”…