SDA 3.4 Documentation for DDLMOD
DDLMOD - Modify or Merge DDL or IDL files
ddlmod -i DDLfile_1 [-j DDLfile_2] [-option]
DDLMOD reads in a
file, then (if ‘-j’ is used) reads in a second file with
additional or corrected specifications, and then carries out any
specified editing. The program then writes out a new DDL file
containing the additions and/or modifications. Diagnostic
messages are written onto the file ‘DDLMOD.MSG’.
The program can also read an
file, which is an expanded DDL file containing additional
elements to describe computer-assisted interviewing instruments.
However the additional elements will not be preserved in the
Merge Two DDL Files
If a second DDL file is specified (after ‘-j’), it is ordinarily
used to supply DDL specifications LACKING in the first file, such
as ‘text=’ specifications for certain variables, or complete
variable definitions for variables not contained in the first DDL
file. By default, any specifications already present in the
first file, such as labels or missing-data codes, are NOT changed
to match the contents of the second file.
However, if the ‘-m’ option is used, the contents of the second
file will MODIFY any specifications already present in the first
The second file does not have to contain all the elements
required for a valid DDL file. In the study description section,
at the top of the DDL file, there only needs to be a ‘title=’
element. For each variable, the file only needs to contain the
‘name=’ element and any elements that are to be added to, or
modified in, the corresponding variable in the first DDL file.
Editing Variable Names, Question Text, and Category Labels
The program can carry out some basic editing functions to make
the output more useful and more attractive for documentation
purposes. The ‘-b’, ‘-l’, ‘-u’, and ‘-x’ options fall into this
category. This editing can be done on a single DDL file
specified with ‘-i’. If a second file is specified with ‘-j’,
the merging of the two files is done first, and then the editing
is carried out on the merged file.
Produce DDL for CSA
The program can also convert a DDL file to the older DDL format
used by the stand-alone CSA programs. The ‘-c’ option indicates
that the output should be in that format. Some newer DDL
features such as multiple missing-data codes and ranges, and
character missing-data codes for numeric variables are not
supported by CSA and therefore cannot be converted. If the input
DDL file contains those newer features, the program will convert
as many specifications as possible for each variable, and will
write a warning in the DDLMOD.MSG file.
SUMMARY OF OPTIONS
Specification of the files
- -i DDLfile_1
- This is the name of the DDL file to start with. It is
always REQUIRED to specify this input file.
- -j DDLfile_2
- This is the name of the additional file containing elements
to add to, or to modify in, the DDL file specified with ‘-i’.
- Any elements contained in DDLfile_2 will modify
the corresponding elements in DDLfile_1.
(Without this option, only the elements missing
in DDLfile_1 will be taken from DDLfile_2.)
- -o filename
- Write the new DDL onto the file ‘filename’ (instead of to
the standard output).
- -w filename
- Write variable descriptions for only those variables that
are listed in the file ‘filename’.
Changing variable names to lower or upper case
- Convert all variable names to lower case (except CASEID)
(Note that the ‘-l’ is a lower-case ‘L’.)
- Convert all variable names to upper case
Editing the question text
- Remove a fixed number of leading spaces or tabs from lines
of question text, while preserving relative indents. (Tabs are
expanded to spaces, before this editing is done.)
For example, if most of the lines are indented by 8 spaces, but
two of the lines are indented by 10 spaces, this option will
remove 8 spaces from the beginning of each line, leaving two
lines with indents of 2 spaces.
- -b length
- Break up long lines of text that exceed ‘length’ characters,
where ‘length’ is the maximum number of characters (including
leading spaces) that should be on a single line of text. The
specified length must be at least 40. (If leading spaces are
removed with the ‘-t’ option, that reduction in line length is
carried out first.)
When lines are broken up by this option, the division is made at
the space preceding the specified line length -- words are not
divided. The names of all variables that have had their text
broken up are listed in the DDLMOD.MSG file.
Editing category labels
- Remove code values from the beginning of category labels.
For example, if category labels had been created (or imported)
like ‘1 Yes’ for code 1, and ‘2 No’ for code 2, this option would
change those labels to ‘Yes’ for code 1 and ‘No’ for code 2.
This also works if the labels include a decimal point like ‘1.
- -v filename
- Write a list of variables contained in the new DDL file onto
the file ‘filename’.
- Produce older DDL for CSA programs
- Display short program help and available options. (The
program will not do anything else.)
- ddlmod -i DDL1 -j DDL2 -o newddl
Add new material in ‘DDL2’ to ‘DDL1’, to make the file ‘newddl’
(but do not replace any specifications already contained in
- ddlmod -m -i DDL1 -j DDL2 -o newddl
Modify ‘DDL1’ by anything contained in ‘DDL2’, to make ‘newddl’
- ddlmod -i DDL1 -t -b 60 -o newddl
Edit the question text in ‘DDL1’ by removing leading spaces and
breaking up lines longer than 60 characters.
- ddlmod -c -i DDL1 -o forCSA
Convert the file ‘DDL1’ into the older DDL format, and make the
|| Data Description Language
|| Instrument Documentation Language
CSM, UC Berkeley
January 25, 2010