SDA files, also called Portable Self Describing files, are files that have been created in a special format that allows them to be used by AskPlus and Visimage on any host or local machine.  They are similar to HP Self Describing files, but do not use the file label to store information about the file.  When you create an SDA file, two files are actually created.  This is important because if you move or transfer the file, you must move both the header and the data files. 

The main reason to use these files is to transfer data from one machine to another and to retain description about the data being transferred.  The most common example would be wanting to use Visimage to create a DBF file in batch.  Since Visimage cannot create the DBF file directly on the host, the first step is to create an SDA file.  The second step is to download both files and then convert them to DBF (or whatever format you wish) using the PC program VISISDA.  This program will convert SDA files to any format supported by Visimage.

Another reason to use SDA files would be to transfer data from an HP3000 system to a UNIX system.  Since AskPlus is available on both systems, SDA is a format that is supported in both environments.

Transferring SDA Files

As mentioned above, SDA files are actually two files.  A header file and a data file.   On the HP3000, the name of the header file is whatever name was specified by the user when creating the file.  The name of the data file is the name of the header file with a 0 (or other digit) appended to the name.  If the name was already 8 characters long, the 0 will replace the last character of the name.  Follow these steps.  In our example, the name of the SDA file is FILENAME.

1. Both files (the header and data file must be transferred using BINARY, not ASCII).

2. Transfer the header file FILENAME and call it FILENAME.sda on the PC.

3. Transfer the data file FILENAM0 and keep the exact same name.
     (Keep it in the same directory as the header file, but do not change the name)

Warning, do not create SDA files in another group (FILENAME.GROUP).  When you do this, the name of the data file in the header file includes the group name and then it cannot be found when the file is transferred to another system.

To convert an SDA file, run the program VISISDA which can be found in the same directory where Visimage was installed.  Open the SDA file and then choose a format in the Conversions menu.  The file will be immediately converted and saved in the same directory as the SDA file with the same name and an extension that reflects the type of conversion chosen.  For example, DBF for a DBASE file.