Varying Record Layout to XML

Sometimes it's easy to convert flat files to XML, and other times it's not. For the simple cases, the comma-separated value adapter or one of its relatives is a good choice. But there are several cases where that's just not good enough. For example:

  1. Simple CSV files
  2. When there is more than one record layout in the file
  3. When fields are fixed-width

So let's conquer those together.

Multiple Record Layouts in One File

Sometimes the problem is that the file contains heterogeneous data — that is, the data in different records has different formats. For example, let's look at a portion of weather-sensor data. In this file, each row is separated by a CR/LF pair, and the fields are separated by exclamation marks. There are three kinds of sensors: rain, temperature, and wind. (And we'll just ignore the fact that the weather seems a little wacky lately.)

TEMP!00:14!75
RAIN!00:35!21
RAIN!00:43!2
TEMP!01:43!75
WIND!02:14!S!16
RAIN!03:03!23
WIND!03:43!SW!13
RAIN!04:41!16
RAIN!05:15!20
TEMP!05:32!76
TEMP!06:38!80
WIND!07:50!NW!5
TEMP!08:29!77
RAIN!08:46!14
RAIN!09:00!12
TEMP!09:24!80
TEMP!10:14!77

If we want to extract this information, and recognize that different rows have different fields and even different numbers of fields, we'll need to match somehow on something unique within each row.


1. Choose File|New|Convert to XML.

File|New|Convert to XML


2. Choose the input file. What we're going to do is take a file that is representative of the format we want to convert, and use it as a template. Once we have the adapter built against it, that same definition should work against any file of similar format. (Yes, for those of you paying careful attention, we're repeating ourselves from the fixed-width text page. But just for this paragraph. Honest.) Note that sometimes there is sufficient context for Stylus Studio® to determine the basic structure and encoding up front, so it offers to "guess" for you based on what it knows about certain common file formats.

New Converter dialog opening heterogeneous file

3. In this case, Stylus Studio® didn't guess the separator properly. It saw a colon ":", and assumed that was it. We'll switch it to an exclamation point "!" by putting one in quotes in the Region Type|Separator property.

Setting the field separator (Click to enlarge)
(click to enlarge)


4. Next, let's name the fields. Put the cursor on the first row, and then double-click the heading row over each field name. We're going to use "sensor", "time" and "temp". For now, let's ignore the fact that some rows have four fields, because none of our TEMP rows do.

Setting the column name (Click to enlarge)
(click to enlarge)

When we're done, it should look like this. Notice the schema tree on the right-hand side? That gives us an idea of the format of the XML that will be emitted by this.

Showing the column names for the first row type (Click to enlarge)
(click to enlarge)


5. Next, we're going to set a filter so that only TEMP rows will emit this XML branch. Right-click on the row indicator in the schema tree, and choose "Edit Node and Pattern...".

Pattern matching menu

From there, change the element name to "temperature" and the match pattern to the regular expression ^TEMP, which means "match all rows which begin (the ^ character) with the phrase 'TEMP'".

Matching against a regexp pattern

Once we do this, the canvas will change to show the rows that match the pattern in white, and the rows that don't match any pattern in pale red.

The results of one regexp pattern


6. To add our match patterns for the next two items, WIND and RAIN, the simplest way is to right-click on the row and choose the "Add Node and Pattern..." option. That will pre-fill the fields, but we'll tweak them a little. WIND will result in an element of "wind" and a pattern of "^WIND", while RAIN will get "precipitation" and "^RAIN". Click on any WIND row and then you can double-click the heading row to set the field names, and then do the same for the RAIN row. You'll see something like this:

The results of all of the regexp patterns


7. Now let's save it and run it against our template file. Choose ConvertToXML|Preview Result, or click on the Preview Result button. If you haven't already saved it, you will be asked to save it now.

Saving adapter definition for subsequent re-use

And here is the final result:

Executing the conversion (Click to enlarge)
(click to enlarge)

These custom-designed adapters — that you build — can be saved and used as input to XSLT, XQuery (especially DataDirect XQuery, or XML pipelines. They can also be called directly from the Data Conversion APIs. So go try this out for yourself by downloading an evaluation copy today.

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