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<TITLE>2.8 File Name Management</TITLE>
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<P><FONT SIZE="5">2.8 File Name Management</FONT><BR>
<P>File names present a host of problems for a program
like FunnelWeb. First, FunnelWeb can generate so many
different kinds of files that conventions must be adopted to
prevent their names from colliding. Second, the
constraints on file names, and even the structure of file
names themselves varies considerably from machine to
machine. These two problems have combined to result in the
sophisticated and rather complicated way in which
FunnelWeb handles filenames.
<P>To summarize, the three problems are:
<P>
<OL>
<LI> What filename extensions should be chosen for various kinds of file?
<LI> What filename inheritance should take place?
<LI> How should FunnelWeb cope with the variations in filename structure
between platforms?
</OL>
<P>These problems are addressed in the following sections.
<P><BR><FONT SIZE="4"><STRONG>Filename Extensions</STRONG></FONT><BR>
<P>FunnelWeb is capable of reading and writing a variety
of different kinds of files. In particular, FunnelWeb must
often operate in an environment where the same information
is stored in many forms (e.g. prog.fw, prog.c, proc.exe).
File extensions are an essential tool in managing this
situation. The default filename extensions chosen for
FunnelWeb are:
<P>
<PRE>
FunnelWeb : .fw
Product : None
Documentation : .tex or .html
Listing : .lis
Journal : .jrn
</PRE>
<P>Lowercase will be used in systems that are case
sensitive.
<P><BR><FONT SIZE="4"><STRONG>Filename Inheritance</STRONG></FONT><BR>
<P>Inheritance in filenames refers to how input and output
files inherit parts of their name from other filenames and
their environment. For example if the command
<P>
<PRE>
fw sloth +J +L +T
</PRE>
<P>were issued, you would expect to see output files
<SAMP>sloth.jrn</SAMP>, <SAMP>sloth.lis</SAMP>, and
<SAMP>sloth.tex</SAMP>. The output file names have inherited
the "<TT>sloth</TT>" part of the argument. In fact,
FunnelWeb implements a comprehensive filename inheritance
scheme, which is shown in the following table. Each filename
is built up by starting at the top of its column in the
table and working down the column, inheriting filename
fields (directory, name, extension) that are absent at that
point.
<P>
<CENTER>
<TABLE BORDER="3">
<TR>
<TD> </TD>
<TD> <STRONG>Script</STRONG> </TD>
<TD> <STRONG>Input</STRONG> </TD>
<TD> <STRONG>Include</STRONG> </TD>
<TD> <STRONG>Journal</STRONG> </TD>
<TD> <STRONG>List</STRONG> </TD>
<TD> <STRONG>Document</STRONG> </TD>
<TD> <STRONG>Product</STRONG> </TD>
</TR>
<TR>
<TD>1 </TD>
<TD> </TD>
<TD> </TD>
<TD> <SAMP>@i</SAMP> </TD>
<TD> </TD>
<TD> </TD>
<TD> </TD>
<TD> <SAMP>@o</SAMP> </TD>
</TR>
<TR>
<TD>2 </TD>
<TD> <SAMP>+x</SAMP> </TD>
<TD> <SAMP>+f</SAMP> </TD>
<TD> <SAMP>+i</SAMP> </TD>
<TD> <SAMP>+j</SAMP> </TD>
<TD> <SAMP>+l</SAMP> </TD>
<TD> <SAMP>+t</SAMP> </TD>
<TD> <SAMP>+o</SAMP> </TD>
</TR>
<TR>
<TD>3 </TD>
<TD> "<TT>.fws</TT>" </TD>
<TD> "<TT>.fw</TT>" </TD>
<TD> "<TT>.fwi</TT>" </TD>
<TD> "<TT>.jrn</TT>" </TD>
<TD> "<TT>.lis</TT>" </TD>
<TD> "<TT>.tex</TT>" </TD>
<TD> </TD>
</TR>
<TR>
<TD>4 </TD>
<TD> </TD>
<TD> </TD>
<TD> <SAMP>+f</SAMP> </TD>
<TD> <SAMP>+f</SAMP> </TD>
<TD> <SAMP>+f</SAMP> </TD>
<TD> <SAMP>+f</SAMP> </TD>
<TD> </TD>
</TR>
<TR>
<TD>5 </TD>
<TD> DefDir </TD>
<TD> Defdir </TD>
<TD> Defdir </TD>
<TD> Defdir </TD>
<TD> Defdir </TD>
<TD> Defdir </TD>
<TD> Defdir </TD>
</TR>
</TABLE>
</CENTER>
<P>The following notes explain the table.
<P><OL>
<LI> Level 1 has the highest priority because it is a
direct specification by the user.
<LI> Level 2 comes next because this is also a direct
specification from the user on the command line.
<LI> Level 3 provides the default file extensions.
Product files do not inherit an extension.
<LI> Level 5 is built into most operating systems'
file specification systems. If you specify file
"<TT>x.y</TT>", it is taken to mean on the default disk in
the default directory.
<LI> Level 4 looks straightforward, but secretly
conceals a difficult design decision. By the time we get
down to this level of inheritance, we know for sure that the
filename has already picked up a file extension. So all that
is left to inherit is the path and the filename proper.
Obviously we have to inherit the filename proper (e.g.
<SAMP>sloth</SAMP> in <SAMP>sloth.tex</SAMP>), but should we
inherit the input file path? If we do inherit the input file
path, files will be placed in the same directory as the
input file. If we don't inherit the input file path, files
will be placed in the current directory. The choice made is
to send all the logging type files into the same directory
as the input file. This means, for example, that
<SAMP>sloth.lis</SAMP> and <SAMP>sloth.tex</SAMP> will generally
land in the same directory as <SAMP>sloth.fw</SAMP>. However,
product files are sent to the default directory (if not
earlier specified), as this is where the action is. In
normal use, the main output of FunnelWeb will be product
files, and so the user will expect them to appear in the
current directory by default.
</OL>
<P><BR><FONT SIZE="4"><STRONG>Portable Structure of File Names</STRONG></FONT><BR>
<P>Another problem with file names is the variation of
their structure between environments. Here are examples of
some of the formats that prevail:
<P>
<PRE>
UNIX /device/dir1/dir2/name
VMS node::device:[dir1.dir2]name.ext;vn
MSDOS device:\dir1\dir2\name.ext
MAC device:dir1:dir2:name
</PRE>
<P>The solution to dealing with these different formats is
to classify them as non-portable and hide the functions that
manipulate them in the machine-specific module of FunnelWeb.
Luckily there are not many such functions.
<P>The main problem is coping with file systems that do
not explicitly support file extensions. With so many
possible input and output files, FunnelWeb all but needs
such extensions. Machines that do not support them pose
difficult design decisions. If the user specifies
"<TT>sloth</TT>" as an input file on such a
non-extension-supporting system, should FunnelWeb look for
<SAMP>sloth</SAMP> or <SAMP>sloth.fw</SAMP>? If the user specifies
<SAMP>walrus</SAMP> as a listing file, should it generate
<SAMP>walrus</SAMP> or <SAMP>walrus.lis</SAMP>?
<P>Some possible solutions are:
<OL>
<LI> Regard the filename <SAMP>sloth</SAMP> as having an
empty extension. It will then default to <SAMP>sloth.fw</SAMP>.
<LI> Regard the filename <SAMP>sloth</SAMP> as having a
blank but full extension. That is, it cannot be overwritten
by inheritance, but it remains blank.
<LI> Provide an extra syntactic mechanism to allow the
user to specify one or other of the two options above.
</OL>
<P>The solution adopted in FunnelWeb is the first option.
Use of FunnelWeb results in lots of files lying around
(e.g. <SAMP>sloth.lis</SAMP>) and it is hard to see how the
user will cope with them all without some kind of naming
discipline. If a naming discipline has to be used, it might
as well be the FunnelWeb one.
<P>Thus the names of all files read and written by
FunnelWeb will have a file extension of from zero to three
letters separated from the rest of the filename by a
"<TT>.</TT>".
<P>The only exception is product files, whose extension is
left undefined. Product files need not contain a
"<TT>.</TT>" and a file extension.
<P>
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