In "USER MAINTENANCE- SU01" --> in the "logon tab" there are 5 different "user type"

1. dialog
2. system
3. communication
4. service
5. reference

Kindly mention the function and role of all the above mentioned user types specifically and hows is one user type different from another.

These are as follows:-

1. Dialogue:- 
  For this kind of users:-
  GUI login is possible.
  Initial password and expiration of passowrd are checked.
  Multi GUI logins are checked.
  Usage:- These are used for GUI logins.

2. System
  For this kind of users:-
  GUI login is not possible.
  Initial password and expiration of passowrd are not checked.
  Usage:- These are used for internal use in system like background jobs.

3. Communication
  For this kind of users:-
  GUI login is not possible.
  Users are allowed to change password through some software in middle tier.
  Usage:- These are used for login to system through external systems like web application

4. Service
  For this kind of users:-
  GUI login is possible.
  Initial password and expiration of passowrd are not checked.
  Multiple logins are allowed.
  Users are not allowed to change the password. Only admin can change the password
  Usage:- These are used for anonymous users. This type of users should be given minimum authorization.

5. Reference
  For this kind of users:-
  GUI login is not ible.
  Initial password and expiration of passowrd are not checked.
  Usage:- These are special kind of users which are used to give authorization to other users.

Tips by :  Rajeev Sharma 

What are the functions of DDIC user in Production system?

There are many functions of DDIC user.

For E.g.. When you configure TMS you won't be able to configure it using sap*. For this you need a user who has access to Data dictionary and ABAP repository Object like DDIC user or user with sap_all and sap_new permission.

2) When we install R/3 in Landscape then we need to configure TMS.  With the help of default user DDIC we can configure s_trnsprt and s_cts_admin. We cannot create new user for our client( Client of Company ) as creating new user gets charged.                                                                                   

Related:

• Changing the default password for sap* user
• Mass Maintenance of Users Profiles

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