How to restrict editing in SP List only to own Items?

I'm looking for possibility to define following options for Sharepoint list. I know it can be done from interface, but how to make if from XML or code? Can I set this somewhere in List Definition or List Instance:

Contributors should be able to create items, but should not be able to modify nor delete items of other users (but edit own items - yes).
Approvers, Site administrators and Site collection administraotrs should have full control over all items

Solution

You are most likely looking for the RoleAssignments property that is available for most scopes.

Suppose you could start with something like this

private void DoStuff() 
{
    SPList list = web.Lists["MyList"];

    // Create custom role
    SPRoleDefinitionCollection roles = web.RoleDefinitions;
    SPRoleDefinition roleDefinition = roles["Contribute"];
    roleDefinition.BasePermissions = SPBasePermissions.AddListItems |
        SPBasePermissions.BrowseDirectories |
        SPBasePermissions.EditListItems |
        SPBasePermissions.DeleteListItems |
        SPBasePermissions.AddDelPrivateWebParts;
    roleDefinition.Update();

    //Creates a new role assignment for a group
    SPGroup myGroup = web.SiteGroups["Team Site Members"];
    SPRoleAssignmentCollection roleAssignments = web.RoleAssignments;

    // SPRoleAssignment accepts a SPPrincipal which can be a SPUser or SPGroup
    SPRoleAssignment roleAssignment = new SPRoleAssignment(myGroup);

    //add a new role definition to the bound role definitions for the role assignment
    SPRoleDefinitionBindingCollection roleDefBindings = roleAssignment.RoleDefinitionBindings;
    roleDefBindings.Add(roles["Contribute"]);

    //Add the new role assignment to the collection of role assignments for the site.
    roleAssignments.Add(roleAssignment);

    // Stop inheriting permissions
    list.BreakRoleInheritance(true);
    list.RoleAssignments.Add(roleAssignment);
    list.Update();
}