Chapter 1

Figure 13.1
There are some similarities between these two types of file-based application – for instance,
in either case, you can open the file by select-and-open from the shell in UIS that support
this functionality.
However, there are real differences also. In load/save-type applications, we tend to think that
the 'real' document is in RAM: the file is just a saved version of the real document. In
database-type applications, we tend to think that the 'real' document is the database – each
entry is just a RAM copy of something in the database. The disciplines for managing the
documents as a whole are, therefore, quite different.
In general, it is meaningful to make load/save-type documents embed- dable, but for
databases, it is less useful. So, databases cannot be embedded (though they can certainly
embed other documents in them).
Finally, there are a few other ways an application handles files:
� An application such as a calculator is clearly not file-based. It neither loads nor saves
the state of its calculation.
� Similarly, there is no need for many test applications to be file-based.
� An application such as e-mail clearly deals with files: it has several directories and files
containing inbox, outbox, other folders, and all the messages. On the other hand, no
sensible e-mail program – including those on the PC – would expose these directories
and files to the user; it would be damaging for the user to try to manipulate them from
the shell (or Windows Explorer).
In all three cases, you can't open an application by opening a file belonging to that
application from a shell application.
So the idea of file-based application has a particular meaning in Symbian OS. Load/save
applications such as Word and so on are file- based and potentially embeddable. Database
applications such as Agenda are also file-based, but can't be embedded. Applications such
as Calc and e-mail aren't file-based.
Important
A key implication of this is that Symbian OS native documents are not
recognized on the basis of their file extension because you don't get file
names in embedded documents.
So a file that's displayed on the Symbian OS shell view (like on the Psion Revo) as Agenda
has no hidden file extension and file save dialogs don't add a default extension for you as
happens on Windows. If an Agenda icon appears next to the file, that's because its internal
format indicates it's an Agenda file.