Applications, tables, fields, and other definitions must have a name, called an identifier. With Doradus, identifiers must begin with a letter and consist only of letters, numbers, and underscores (_). Letters can be upper- or lower-case, however identifiers are case-sensitive (e.g., Email, Log_Data, H1L4). An exception to the first-letter rule are alias names, which must begin with a dollar sign (e.g., $SalesEmails).Pre-defined system identifiers begin with an underscore. Because user-defined identifiers cannot begin with an underscore, all system identifiers are reserved. Example system identifiers are _ID, _all, and _applications.