The built-in datatype text is like string, but for arbitrarily long (in theory) text values. The tradeoff is values of this type cannot be used as selection criteria in queries, i.e. you cannot match a value of Type:Text, but you can ask what has a value for some property of this type, and you can display the property in query results. Nor can you sort a query on a property of Type:Text (although its clickable column heading in table format will work since this is implemented in client-side JavaScript).